HOTRODDIN’ THE PREDATOR

Tue, 5 Jun 2012 09:21:41 -0400

By Gary Costanza

Every once in a while, a manufacturer of these clones will change something that will make any good cloner stop and say, HEY, Maybe I can use that for racing. OK, maybe that happens all the time and in this case it’s the new 212cc Predator motors from Harbor Freight. Priced in the neighborhood of $159.00 and less if you can find them on sale, these base motors come with some real nice surprises.

The first one is obvious. Its 212cc’s compared to 196cc or 208cc for all the other 6.5hp clones, making it the biggest so far. And bigger is better, Right? Let’s see.

Coming in with a 70mm bore and a 55mm stroke makes this bad boy “King of the Hill” when it comes to size. The 196cc clones have a 68mm bore and a 54mm stroke while the 208’s are 70mm bore and 54mm stroke. OK, so I’m thinking this little shining black gem is stroked and bored right out of the box. How could I resist taking a peak to see what else could be hiding beneath that menacing black exterior?

Another pleasant surprise was the castings and finish. Unlike the grainy castings of many of the other clones, the Predator is closer related to the Honda as far as detail and quality. It comes with the usual features found on most clones. lt has a governor system to 3900rpms, on/off switch, low oil sensor shut off, gas tank, air box and filter system, check oil caps at both ends, spark arresting exhaust system, pull starter and meets EPA emissions standards. What a deal, right? Let’s take a look.

First, we need a baseline horsepower and torque number. That means a trip to see Dr. Dyno and “The Search for the Truth” begins. Before starting any process that involves change, it’s always good to have an idea of what you have to start with. And a dyno is as good as it gets for this. In order to meet EPA standards you will find these clones are jetted very lean. In fact, they are too lean for what we want. Usually, the clone’s main jet is #70. I have found that #85 - #90 works better at most elevations and should get you in the ballpark and on your way to making safe and reliable power.

The other jet of concern is the pilot jet. And that is located just under the idle screw adjuster. Normal pilot jets are in the range of .014”. We want .020” to richen up the bottom end, and help with acceleration off idle, and through the low part of midrange just before the main jet takes over.

So off comes the gas tank to be replaced with an aluminum top plate for added strength. Then the air box and stock filter to be replaced by a K & N racing style air filter and adaptor. Next, let’s complete this motor’s breathing improvements and get rid of that very restrictive exhaust system and spark arrestor for an open pipe into Dr. Dyno’s exhaust analyzer sensors. Add some of your favorite oil and we are ready for our appointment with the good Dr.

Our Predator fired right up without hesitation and ran smooth for its 30 minute break in. The new jetting was much to her liking with smooth acceleration and crisp throttle response. Ungoverned, the Predator was very anxious to turn more rpm’s than the manufacture would like to hear about. After warming up to a head temp of 275˚ I laid the hammer down and let Dr. Dyno take over. The manufacturer stated 6.5 horsepower at 3600rpms. With the improvements we did our test results were closer to 9 horsepower at 3600rpm with maximum torque pulling 14.10 ft. lbs. at 2300rpms. The maximum horsepower of 9.83 was achieved at 4700rpms. Power started dropping off at 4900rpms and we hit a wall at 5600. I believe some valve float was limiting our revs after that.

So before we can search for more power we need to address the issue of the valve train. I am targeting the 6500rpm range for this build and will be changing from gas to methanol as our fuel. I will do another dyno run to see just what the change in fuel alone will do to the power curve.

My Initial impression is some good power making potential exists with this bored stroker as a base motor. It’s time to see what’s under all those aluminum covers and tins starting with the head.

You don’t have to remove the head just to change the springs. However, I’m going to install new SI stainless steel valves while I have the Predator apart. Like all clones, there are only 4 head bolts securing the head to the block. No surprises here. This has always made sealing these motors challenging when modifications to compression and bore have taken place. There are many suppliers who have seen the need for us cloners and have come to the rescue and are making all kinds of high performance “plug n play” go fast parts. Like modified heads, racing cams, forged pistons, roller rocker arms, light weight flywheels, and the list goes on.

This Predator head will have stock size stainless valves, 25mm intake and 24mm exhaust with automotive style split keepers. Those 10.8lbs. stock valve springs will be replaced with 26lb springs to control that valve float. And 1.3 ratio rockers to give us a bit more lift, and some mild cleanup of the ports.

To help support the valve trains extra spring and rocker pressure we will replace the mild stock steel pushrods with a set of chrome molys. Thanks to the suppliers we now have choices from adjustable aluminum to “Do it yourself” kits to make any length you want. This will come in handy if you do any milling of the block or head.

Once you pop the top off, you will notice 2 more surprises. First, the piston position in the cylinder at top dead center is just .003”from the deck. Now any cloner worth a roll of duct tape knows what this means. Most clone piston positions are more like .030” below deck requiring longer rods and different pistons to get any compression. Even though this is a dish style piston, a .003” “in the hole” piston is a huge advantage.

The second surprise is the Predator comes with a .050” thick head gasket. With the wide variety of head gaskets from suppliers on the market today, this is another area where we can pick up some compression by using a thinner one. In this case I will be using a large profile .016” copper head gasket. Some form of gasket sealer is always a good idea. Now that we have increased the compression we need help keeping the lid on. High strength metric stud kits are available and do a great job in this area. Metric stainless steel bolt kits are also available and work well.

Now that we have made the needed changes to the head its time to reinstall and torque it all back down on the block. The stock head torque values are 17ft. lbs. With the studs you can go up to 24ft. lbs.. This will help in keeping the beast sealed.

The switch from gas to methanol will take some carburetor jetting changes. However, there are many suppliers who will be more than happy to help you with this fuel conversion. They sell “Plug n Play” carburetors that take all the guess work out of choosing which jets to use. The price ranges from $49.00 to $125.00 for blueprinted carburetors, depending on your needs.

Now, if you happen to be a member of the “PoBoy’s Greasy nails” club, like me, then you’re going to do this yourself and save the money for nonessential items like clothes or rent.

And all you really need to do is drill out the pilot jet, the emulsion tube or E-Tube, and the main jet.

Depending on where you live will determine which jet size combo works best. Some experimenting will be needed. The range for the pilot is .026” - .032”. This will effect off idle and early acceleration out of the corners. The main jet range will be from .056” - .064”. This controls the mixture at wide open throttle or WOT. The E-Tube will need to be bigger than the main jet. If it’s not already, than increase this to a minimum of .074”.

In case you haven’t figure this out already, then let me tell you this isn’t going to be good for your mileage. Expect to use twice as much alky as gas. That lost mileage however, will be replaced by a big ole grin when you hammer down. Now, in order to “feed the beast” with its new found appetite we will need to install a fuel pump.

All fuel pumps that we use for the clones are pulse activated. So, we need to pick up a pressure signal from somewhere. Again, our friendly suppliers step in with this behind the carburetor pulse fitting adaptor that will give us just the signal we need. You can pulse from the crankcase or valve cover as well, but that gets messy keeping the oil out of the pulse line.
One last issue needs to be addressed before we can fire up. The cast flywheel is not intended for use above 4000rpms, so we once again turn to our clone parts suppliers for a safer flywheel. And this comes in many forms.

As of this writing there seems to be some issues on which flywheels fit the Predator best, so check with your local dealers before you order. And while we have the old cast flywheel off we can use modified keys that will advance the ignition timing from 20 degrees stock to at least 28 degrees or more. These modified keys come from suppliers in advancements of 2˚, 4˚, 8˚ and 12˚. Alcohol loves advanced timing and 30-32 degrees seems to be the “sweet spot” for circle track racing. If drag racing your minibike is what you do then 34-36 degrees would be a better sweet spot for you guys.

Be sure when you install your new flywheel that you move it clockwise so the new modified or cut key rest against the left side of the flywheels keyway. This will advance the position of the magnet in relation to ignition timing.

All that’s left is to set the coil/flywheel air gap as per the manufacture spec sheet that will come with the wheel.

A word of CAUTION is needed at this point. If your going to pull start this modified Predator, you will need to slowly pull the rope until you feel the compression stroke before you yank, Then yank and let go. If it backfires, and they do, it will pull the rope/handle right out of your hand and that really stings.

When we get this all done our Predator will start to look more like a racing motor than something that belongs on a log splitter.

Now our Predator is ready to face Dr. Dyno for the second time. With a new thirst for power there is nothing left but the truth to tell us how we did.

The first thing you will notice is how long it takes to warm up. Exhaust temps have been reduced from 1500 degrees to a near frigid 1200 degrees. Condensation will start around the carburetor as little droplets of water when the cold mixture runs through the bore. Head temperature was hard to get above 225 degrees when Dr. Dyno took over.

While guzzling alky at an incredible rate your beast pulled a maximum horsepower of 12.13 at 4800rpms and a maximum torque of 16.03ft lbs. at 2200rpms. That’s an increase of 2.3 horsepower over gas and it increased rpm’s by 700. This beast on alky easily pulled over 6400rpms. The torque not only increased by 1.93ft. lbs. but the maximum occurred 100 rpms lower. Lowering the torque’s rpm range is always a good thing.

Any cloner would be very pleased with results like this. With some carburetor wizardry, a pair of springs, and a new fuel, our Predator is ready to be set free in the wilds to prowl on any unsuspecting ANIMALS that may be lurking around at the local tracks. And we haven’t even opened up the crankcase.

Not yet anyway, but I’m having dreams of racing cams, bigger carburetors, flat top pistons, billet rods, roller rockers, chrome moly, and who knows what other ‘Go Fast” parts are out there. I’m seeing a part 2 here.

Clones, They’re

ADDING NEW LIFE TO YOUR CHASSIS

Tue, 5 Jun 2012 08:48:31 -0400

Are You Listening?
By Mike Unger

I know times are tough all over, and finding a budget for a new chassis might be completely out of the question. So I suggest you simply look at what you have and consider a bit of restoration work. You might find out that the chassis you already have just needs some elbow grease and TLC to get it in top shape for the upcoming season.

My son’s kart is a perfect example. It is a 2008 Kosmic T11 that I raced in Tag Masters and then he raced this past year in his first year in Yamaha Junior. The chassis works well, he still likes the way it handles and we ran quite successfully with it at the local series at New Castle Raceway Park. After a year of running local sprint races we finished the year with a 225 lap endurance race and needless to say it is in serious need of some work to get it in tip top shape.

Before you dive into a full refurbish you need to make sure the chassis is worth the effort. The first place to look is the underside of the kart. Look for frame tubes that are ground flat due to contact with the track. If the tubes are only slightly damaged the integrity of the chassis is still acceptable and handling will be unaffected. But if the tubes are ground down to a point that there is only a few thousands of an inch of steel left before it goes through it is time to shop for a new chassis or at the least a new frame. Also while you are inspecting the frame look for cracked welds. It’s something you will do again after the frame is thoroughly cleaned but right now look for more obvious cracks. Most cracks will appear at the joints where two tubes come together or where brackets are attached. If you find a crack in the middle of a tube you should be more cautious. Repairing a tube mid length could alter the way the frame flexes and cause troubles on the track. Again look things over and decide for yourself how to proceed. If after the initial inspection you have decided this chassis is worth the effort it’s time for a complete tear down. You will need a notepad to list obvious things that need replaced as well as lots of rags, cleaning supplies, and patience.

For the tear down I suggest starting at the rear of the kart and working your way forward, starting first with the rear bumper. In my case the Kosmic has a full length plastic bumper that is attached to the frame tube though brackets. Remove the plastic bumper from the brackets, carefully inspecting the bolts and brackets for excessive wear, bent bolts and simply worn out components. If you find a bracket or bolt that needs replaced write it down on your notepad. Carefully organize your parts as you remove them. I suggest using a couple plastic bins to keep things organized.

After you get the rear bumper off its time to start into the axle assembly. This area tends to be the most critical and the most messy, rubber gloves may be in order. Remove the wheel hubs, sprocket carrier, keyways and inspect for cracks or stripped bolts. Make a note to replace as needed. After the hubs are removed spin the axle and carefully look for a wobble in the axle. The human eye has the ability to detect a difference down to a couple of thousands of an inch. If you see a wobble make a note that you will need to send the axle out to get straightened before reassembly. Just ask at your local kart shop for someone who straightens then. Often you can get it done for a fraction of the price of a new axle. Next remove the axle from the bearing cassettes. This will require loosening the set screws in the bearings, as well as the brake disk hub. After you have removed all the set screws and loosened the brake disk hub you can remove the axle. To do so you will need a large rubber mallet and some effort. Make sure to slide the axle out towards the engine side of the frame. After you get the axle to move far enough the brake disk keyway can be removed and the axle can be completely removed. If after initial hammer blows it doesn’t come free you should check again for set screws you missed or a sticking brake disk hub. Sometimes a screwdriver gently tapped in the slot in the brake disk frees things up. If that still doesn’t work you might need a friend to help hold things in place while you wind up and drive it out. Just remember that it was assembled by hand once before, it can be disassembled.

After you remove the axle, set it aside and remove the bearing cassettes from the frame. For most chassis this will also require removing the rear brake caliper assembly. While you are at it I suggest removing the entire brake system and setting it aside. We will inspect that system later. Once you have the bearing cassettes removed set them aside as well for further cleaning and inspection.

Next its time to remove the seat and all of the seat struts. When doing this, carefully check for cracks, elongated holes and worn bolts. Cracks and elongated holes can be repaired with a fiberglass repair kit. Bolts need to be replaced. Set the seat aside and move on to the fuel tank and floor pan.

Before you remove the fuel tank I suggest you cut the fuel lines away from the tank and discard them. Fuel lines tend to harden over time and need to be replaced periodically. I suggest discarding the fuel filter as well. With the lines removed unscrew the large wing nut to remove the fuel tank or if your tank is bolted to the floor pan remove as needed. Carefully inspect the tank for thin areas, weak seams and cracked fittings. Make a note to replace as needed. Fuel tanks tend to collect lots of dirt and grime over the race year but often can be cleaned up to look very good. If your tank in yellowed from having fuel left in it for too long it might be time to consider a replacement.

The floor pan is next and the bolts that hold it in are likely ground down or full of dirt. These are very likely the bolts that will need to be replaced at least once a year. Getting them off can sometimes be a chore. Vise grips and patience is the only suggestion I can offer. After the floor plan is out you have easy access to the driver fairing and steering shaft. Remove the steering shaft lower bushing with a snap ring pliers as well. As with other parts set them aside for inspection and cleaning later

After the steering shaft all that is left is the front bumper and pedals. Carefully inspect the pedals for excessive wear and tear. The bumpers usually slide over tubes in the front and are fastened with bolts a simple tap with a rubber mallet and they will pop off for you.

OK, now that the kart is completely dissembled it is time to clean and inspect each component before re-assembly. I suggesting cleaning and inspecting each component individually before putting them back on the frame. For this activity it is recommend some rubber gloves, a parts washer, a cleaning agent (WD40 is what I use), an old toothbrush, and lots of rags. Don’t use brake cleaner on any painted surface as it will damage the paint. I also suggest replacing old nylon lock nuts with new ones as they tend to loosen up after being on and off several times. New nuts and bolts are cheap insurance against a problem on raceday.

The first thing to clean and likely the most time consuming is the frame itself. Use lots of cleaner and use the toothbrush to get into those hard to reach areas. Take your time and do a good job. After the frame is free of all dirt and grime wipe it down with a clean rag and place it on the kart stand. Now we will polish the frame up while inspecting each and every inch of the frame. Cleaning the paint is a step that will really make a difference in how good your frame looks in the end. I use Mequires paint cleaner for this step. You can find it at any auto store and you use it just like rubbing compound. It gently removes stubborn grime and restores the luster in the powder coat. Concentrate on one frame tube at a time and as you clean carefully look for cracks. If you find one you will need to get it repaired. To properly weld the frame you will need to get it TIG welded by a good welder. The best place to find such talent is in a race shop that builds full tubular frames. Before you take the frame, be sure to remove all paint from the cracked area. This will ensure that the weld will be clean and solid. In my case the right side seat strut broke right around the tab. A simple clean-up and a trip to my buddy who builds sand dragsters and it was fixed. After the frame is completely cleaned up and repaired as needed it is decision time. If the frame’s paint was able to be cleaned up enough for you liking you can proceed with the rest of the assembly. If not you should consider re-powder coating the frame. Do a search on the internet for powder coating in your area or ask around at your local kart shop for places that do it. You can usually get it done for around $300 in most any color you like.

With the frame now complete it is time to start putting parts back on it. When I take parts off I don’t clean them until it’s time to put them back on. Using this technique I can focus on each and every component and make sure it’s right before moving on to the next part. I like to start with the rear axle assembly since it the most time consuming and messy.

The rear axle bearings and cassettes need the attention first. The bearings can be removed from the cassette by turning them 90 degrees to the cassette and lining up the slot on the cassette. After they are removed carefully wipe any grease and grime from around the bearing dust shield. Be careful not to push the grime into the bearings further as this will make your job bigger. After the bearings are cleaned spin them in your hands listening for grinding and well and feeling for excessive play. If what you hear sounds like someone grinding coffee or there is lots of play in the bearing I suggest replacing the bearings. Of course you can try removing the dust shields and cleaning it all out but since these bearings are very important to the performance of your kart replacing them with new ones is money well spent.

Next clean up the cassettes and look carefully at the interface between the outer race of the bearing and the cassette. Often you will find deep scratches and grooves in this area. I suggest thoroughly cleaning and then using a scotch bright pad to smooth things out. After everything is cleaned up put the bearings back in the cassettes. Use light grease between the outer race of the bearing and the cassette to help the bearing adjust as the chassis flexes. Put the cassettes back on the frame using the original bolts as long as they are in good shape. Remember to use a thread locker of some kind to keep those bolts from backing out. Do not torque the bolts down until after we put the axle in.

Now it’s time to work on the brakes. Brakes being an important safety item and rebuilding them not necessarily a trivial matter, I suggest that unless you are very mechanically inclined you ask your local kart shop for help with the rebuild. Of course if you are comfortable a brake rebuild kit is available from your chassis manufacturer. Carefully disassemble the brakes, drain the brake fluid, replace seals and thoroughly clean. Use brake cleaner and be mindful to make sure all the components are surgically clean. During reassembly make sure to use thread locker as you did for the bearing cassettes. Also be sure to use the proper type of brake fluid in the system. Most brake fluids do not mix with each other. When in doubt consult your chassis manufacturer for help.

Before the axle goes in you will need to clean up the brake rotor. I suggest removing the disk from the hub and cleaning both with a very fine steel wool. Don’t rub too hard as you will remove the anodizing on the aluminum hub. Reassemble the rotor and hub using new steel locknuts. Never reuse them and never use nylon locknuts on the brake disk as they will melt from the heat.

The axle takes a lot of abuse in a kart and in order to make it easier to get in and out you will need to apply some elbow grease to it. I suggest using a small file to remove the burs caused by the set screws and medium grade sandpaper to smooth out the areas where the hubs attach. This will take a little time but will make the axle install much easier. After it is ready, slide the axle into the bearings through the brake rotor and into the far side bearing. Don’t forget that before you slide it all the way through you will need to put the brake rotor keyway in place. Now torque down the bearing cassettes bolts and check to make sure the axle spins freely. If it doesn’t, gently tap the cassettes with a rubber mallet. Often the bearings need a little bit of force to get everything aligned. After the axle is through, use a measuring tape to make sure the axle is centered in the frame. Now line up the set screw holes with existing bolt locations on the axle and tighten down the set screws. Don’t forget to use thread locker on the set screws. Now is a good time to safety wire the brake disk and caliper as well.

Next up is to move to the front of the kart. Put the front bumpers back on, along with the pedals. Carefully inspect the bolts that hold the pedals. They tend to wear over time and generate excessive play in the pedals. Replace the nylon lock nuts with new ones too.

For the steering shaft make sure to remove and inspect the lower support bushing in the frame. For most karts you will need to remove a snap ring to get it out. Once out clean it thoroughly and check for excessive play. If needed replace. Too much play will cause for inconsistent toe measurements as well as a sloppy steering. When you put it back in place be sure to check to make sure the snap ring is seated properly. If it isn’t seated right it could be a safety issue. Replace the nylon lock nut and tighten. With the floor pan out of the way this is the time to safety wire or put the E clip on the end of the steering shaft.

With the steering shaft in place it is time to put the floor pan back on. The floor pan on Noah’s kart had a big sticker covering the whole thing. When new it looked very sharp but after years of use it is looking pretty rough. I removed the sticker and with some brake cleaner removed the adhesive that was still stuck to the aluminum. Then with some fine steel wool I cleaned it up and made it look almost like new. Attaching the floor pan will require new bolts and nuts. These bolts take lots of abuse so don’t cut corners here. In order to keep the floor pan from rattling I always use rubber washers between the frame tabs and the floor pan.

Now it’s time for the spindles and tie rods. Inspect and clean the spindles closely. Pay careful attention to the bearings in the spindles that support the kingpin. These small bearings take a huge amount of abuse and usually need replaced yearly. Also don’t forget the bearings in the wheel hubs if that is the style on your kart. Inspect the tie rod ends looking for excessive play as wheel as bent ends. It’s pretty easy to overlook a bent one in the rush to fix a bent tie rod at the track. Assemble the tie rods using new nylon locknuts. Alignment will come at the end.

Now let’s talk about the seat. The seat takes a lot of punishment not only from dragging over that high curb you like to hit but it also supports quite a bit of load on the racetrack. Check for cracks around mounting locations, elongated holes, cracks and damage to the bottom of the seat. If you don’t find anything then a simple scrubbing with some brake cleaner to remove the grim and your seat will be ready to go back in.

If you did find some areas in need of repair I suggest a visit to your local automotive parts store to purchase a fiberglass repair kit and some rubber gloves. Make sure you clean the area to be repaired thoroughly and follow the directions on the box. I suggest 3 layers of fiberglass mesh for most repairs, more for big areas. To fix elongated holes simply put some tape over the hole from the inside of the seat before you apply fiberglass over outside of the seat. Make sure the fiberglass is completely dry before you re-install the seat in the frame. Like the rest of the kart, make sure you use new nylon lock nuts when you re-install the seat.

Now it’s time for the rear bumper. In my case it’s a full length plastic bumper that is fastened to the frame with long bolts that pull 2 wedge-like plastic pieces together that expands against the inside of the frame tube. Completely disassemble the wedges and clean them completely. Also swab out the inside of the frame tube to make sure there is no residue that would make the insert slip out on the track. Also check those long bolts, they take a lot of abuse and can bend. If they are replace as needed. Disassemble and clean all related pieces that attach the bumper to these long bolts. Inspect for wear and like the previous parts replace as needed. The rear bumper also needs to be cleaned. For this I used WD 40 and a small scrub brush. Scrub all the dirt and grime off using the WD40 then clean the WD40 off with brake clean. After all the parts are completely clean re-assemble. Use blue threadlocker on the nuts on the long bolts when you tighten things down. Don’t forget to replace the nylon nuts.

The final parts of the kart to clean up is the bodywork and nerf bars. If you have a sticker kit you will need to decide if it’s time to replace them or not. Decals take a beating, but they are really a great way to make an older kart look great. In my case and with the help of NKN and Decal Works I replaced the beat up original Kosmic stickers with a custom Decal Works kit. Installation is easy but does take some time and patience. Just follow the well written directions and your bodywork will look like new.

So there you have it, how to refurbish an older kart and not only make it look like new but also make it perform like new. In my case, minus the sticker kit, I spent about $20 in new nuts and bolts, $15 for a fiberglass repair kit, and $10 in cleaners and such. That is much easier on the wallet than a new $5000 chassis.t keep on coming.

BATTLE OF THE CLONES, PART II

Tue, 5 Jun 2012 08:29:58 -0400

Revenge Of The Clones
By Gary Costanza

If you are not a follower of International Trade Agreements and Copyright laws you may not be aware of the lawsuit that Honda filed some time back against others that well, let’s just say have made their products too similar to many of the wonderful products Honda has brought to us here in the United States. We ‘cloners’ like to stay neutral on these political indifference’s in commerce and can’t see why everybody just can’t get along. If you know a bargain when you see one, then you’re a cloner at heart or as my wife say’s “Sneak’s, you are cheap.” We ‘cloners’ have learned to accept whatever the industrial world decides and try to make that fit in our racing lives. So what does Honda winning an International copyright lawsuit mean to a cloner like me? I like to call it, “The Revenge of the Clones.”

Let me introduce you to a couple of newcomers that resulted from Honda winning that lawsuit. The new nightmare for tracks with cc rules is a 212cc black clone called “The Predator” from Harbor Freight. With a bore of 70mm and a stroke of 55mm you might say it’s a bored out GX200 mini stroker. With a 68mm bore and a 54mm stroke the Honda is giving up some displacement so “Who’s your Daddy” now? And then there is a new Yellow and black 196cc clone from Champion with a crazy new valve and rocker design. Yes sir, why that’s just plain cheap ‘eye candy’ for a cloner right there. Now if you just happen to be a “parts swapper” like myself don’t go gettin’ all excited just yet. Hardly any of the parts are interchangeable anymore. A cold, hard fact that us cloners have to accept because of all this legal stuff.
So how cool would it be to let Honda’s workhorse of OHV 4 cycle motors, “The legendary GX200” battle it out, not in a courtroom, but in a dyno room with only Judge Dr. Dyno “The Truth Giver” to hand down the final verdict. No lawyers, no jury, no big money, just how fast can you spin a 300 pound steel wheel against 2 of the clone world’s latest spawns that have emerged from out of the industrial ash caused by this very high court room decision somewhere far, far away from you, me and the Berkshire Mountains of Massachusetts.

The GX200, which you can see at just about any kart concession will now have to deal with these 2 reborn copies of itself and I’m afraid more are coming. But for now its time to get ready to face the dreaded Judge Dr. Dyno and for that they all need to get battle ready. This will consist of removing the governor, gas tank, exhaust system, low oil sensor, and air box. I will limit the maximum rpm’s because of the cast flywheels. Most steel cast flywheels are only rated to 3900 rpm. The Judge often needs to inflict pain and pressure above the 5500 rpm mark in order to seek out the truth. Timing will be set at 20 degrees and 87 octane (regular) gas will be used. The carburetors will need jet changes to provide a more suitable fuel mixture for the battle. The pilot jet will be increased to .020” or .50 mm and the main jet will be drilled to .035”or .89mm. To help our gladiators get enough air for the new jetting during the battle, a K&N style air filter will be used. The exhaust system is open to a chamber where the Air/Fuel ratio sensor is located. We will be monitoring the A/F ratio through out the battle. An aluminum top plate will be installed where the gas tank was located for back support and strength. This is all part of the battle armor and support package that most engine builders install to help keep things together.

As similar as they are each OHV motor has some very important differences. The grandfather and the original Honda GX200 has not changed in a long time. This one comes from NRracing out of Michigan and list price is about $300.00. It’s still the same old reliable equipment and replacement motor that we have all grown to trust in our power and sports industry. Quality is among the best and Honda has mastered the art of casting aluminum. And now, there seems to be more polishing going on than before. The GX200 has sidecovers that sparkle and the muffler/spark arresting system has a stamped steel support bar that attaches to the head. This is a great feature and I don’t know anybody who hasn’t broken a muffler off at the pipe neck from vibration. Now that’s something the clones forgot to copy. And whoever is doing the welding of these muffler pipes at Honda really know how to lay down a “row of nickels.” The carburetor is a Keihin which Honda has been used in many of their motorcycles and other vehicles. There is only a half turn of idle adjustment on the idle metering screw because you’re limited by the carburetor body. This is still better than the Champion or Predator which have no adjustment. They still come with the “old style” 4 bolt valve cover in the same shape it’s been from the beginning of time. The finish work is excellent and with a red sidecover, white gas tank, and black trim, the Honda color tradition seems to be in tact. In the past pressure venting from the gas cap has been a problem. Honda’s gas cap is massive on this model. It’s chrome and handles pressure venting very well. The metal and plastic clone gas caps are known to be problematic when used for racing.

Also coming in at 196cc out of Hamilton, New Jersey for under $200.00 from Adam’s Equipment Rental is the Champion Products, OHV, 6.5hp clone utility replacement motor. This motor comes with a valve train that is very different from Honda and all other clones. The Champion has cast steel rockers with the lash adjusters on the valve end of the rocker, unlike stamped steel assemblies which adjust from the center by raising or lowering the rocker pivot point. The rocker pivot point in the clone rockers can crack and fail when modifying these motors. The Champs rockers are shaft mounted which eliminates any sideplay or wobble that is associated with all stamped steel rocker systems. The valve cover is deeper than all the others to make clearance for the valve train assembly. I have heard some inventive weekend garage mechanics buy just the rocker system to replace the stamped steel rockers. This system will fit other clones, but you didn’t hear that from me. The overall appearance of the yellow and black is striking. The gas shutoff is located under the tank and not on the carburetor like all the others. The engine shutoff is a nice automotive style toggle switch that is located with the gas shutoff and housed in a dashboard style setting.

This replaces that old turn style on/off switch found on most clones that is always trouble after some run time and vibration. The carburetor is stamped CPE and is a new design. Although similar in appearance and function there is no gas shut off. As stated earlier, that’s under the gas tank. The air filter system is a long narrow paper element style that has duel intakes. This Champion has got some very nice features not found anywhere else. Let’s see if it has got the guts too.

And last, out of Albany, New York donated by my driver the almost famous “Johnny UPS” and selling for about $160.00 comes Harbor Freight’s new replacement for the Greyhound called the Predator. This bad boy has the biggest gun at 212cc. Its appearance is very similar to the Honda’s from the outside and it’s all black, sleek, and mean looking just like a Predator should be. It comes with a Huayi carburetor that has no idle adjustment, but sports a sleek looking airbox about the same size as the Honda. The aluminum castings are better than the Champion, but not quite as good as the Honda. The engine and gas shutoff are the same as the Honda but the muffler/spark arrestor is like the Champion and doesn’t have any extra support. Other than a little extra stroke and bore the Predator looks almost like a black Honda so beware of what you can’t see.

So now that we have met our 3 gladiators, it’s time to get ready for the battle. The first part of the dyno prep is getting rid of all that utility hardware like the gas tank, airbox, governor, low oil sensor, and muffler. Then our trio is fitted with matching top plates, throttle assemblies, airfilter adaptors, K&N style filters and 500ml of fresh oil. It’s not a bad idea to check all the bolts you can reach for tightness and recheck them after each run. Things can get loose in a hurry at near twice the manufacturers suggested rpm range. “Let the games begin.”

The first of our contenders to face Judge Dr. Dyno will be Harbor Freight’s “The Predator.” On the market for just a couple of years, the Predator has made quite a lot of trouble for local tracks and sanctioned events that have rules about 196cc maximum displacements. Because of its 212cc advantage, what racer would not want to investigate this “new kid on the block” a bit further? For uses that don’t have rules, like minibikes, and power equipment, the added displacement is a welcome addition with the promise of even more torque than these motors are noted for.

After a 30min break in with the new jetting, improved breathing, and exhaust scavenging, the big bad Predator settled in at a reasonable idle. This could be improved with an idle adjustment screw, but sorry, somebody glued that in place. I’m guessing it was a secret EPA agent. Off idle acceleration is very crisp with no hesitation. It was obvious, that this clone was here for some serious playtime. It’s always fun to hear that 4 cycle motor clatter without all that exhaust noise. You can hear all those parts doing their own thing in harmony. The Predator’s noise level and clatter was normal for a clone.

Warmed up to a head temperature of 275 degrees I dropped the hammer and Judge Dr. Dyno took over. The Predator shocked the Doctor until the Premier Titan clutch hit stall speed and locked up around 2500r’s. The Predator struggled a bit from lock up until 3300 rpm when things smoothed out and the big “P” man laid down the torque to a maximum of 9.83 horsepower at 4700 rpm to start this battle off. ) The power band started at 3300 rpm and ended fast at 5000 rpm. Maximum torque during that period was 13.5 foot pounds. The air/fuel ratio leaned out slightly at 3000 rpm but hovered just about 12 until 4100 rpm. As the cam ran out and the springs started to float the valves, the carburetor leaned out then rebounded back to rich when the Predator had absolutely nothing left to give but the flywheel inertia. Everything powered down and the pull went without issues. The Predator maintained idle and acted like it was just another day on the cement mixer.

Next up and shipped out of Hamilton, New Jersey by Adams Equipment Rental is a little known yellow and black clone from Champion Products Equipment that has the same bore and stroke as the Honda. This clone decided to change the entire valve system and carburetor so when you start up the Champ the first thing you will notice is how quiet it is. The idle was velvet smooth but stumbled off idle and lumbered to 4500 rpm like it would rather have been running a pressure washer. After a 30 minute break in, “The Champ,” with the same new jetting as the Predator showed some signs of life. That off idle bog was completely gone and throttle response was razor sharp and clean. The Champ was ready.

The CPE carburetor ran leaner than the Huayi of the Predator. The CPE remained in the 14 range and like the Predator, the Champ also leaned out hitting stall speed, but recovered nicely at 3600 rpm. The Champ calls home from 3600 rpm to 5000 rpm and pulls very strong here. Everything comes together at 4600 rpm for a whopping 10.50 horsepower. After powering down the Champ settled in to a nice idle ready to perform whatever comes next on the job site. This sends the big bore stroker, the Predator, packing and looking for a future in farm equipment or minibikes. The new, for now,” king of this hill” is “The Champion.”

And waiting in the wings all this time and dressed to kill comes my personal hero. Honda and I go way back to my first real motorcycle and the saying. “You meet the nicest people on a Honda.” I always hated that saying. I had a tricked out 1966 305cc Super Hawk SS that got me to high school and back, but that’s another story. Our GX200 started on the first pull and ran great through 30 minutes of break in. No hesitation or stumbling at idle or off idle, just good old Honda reliability. Strapped to Judge Dr. Dyno the GX200 reached 275 degree head temperature and went to full throttle. The Keihin carburetor was just about perfect with an air/fuel ratio around 13 and only leaning out slightly at stall speed. The new jetting worked very well with the Honda’s better breathing and power came on smooth and steady from 2500 rpm to 5200 rpm before gradually giving up at 5500 rpm. The Honda made a maximum 9.29 horsepower at 4300 rpm and seemed to produce its torque early. After powering down the Honda slipped into a steady idle waiting to be called upon for the next task. Although failing to make the most horsepower you can bet this Honda will make 9.29 horsepower for a very long time.

The clone world is full of underdogs and long shots but every once in a while one comes along like “The Champion” and takes our clone world by surprise. All 3 motors performed flawlessly and didn’t appear to bare any scars from their encounter with the dreaded Judge Dr. Dyno. Not every clone that has faced the dyno has left in one piece, but those that do are headed for a more glamorous life than construction and farming. These 3 have now proven to be good enough to be the race gladiators of the near future in someone’s dream.

In the next battle I have the forgotten OHV LCT208, against a new 208cc simply know as the “Z”, and a new comer from Lifan. And the clones jus

BATTLE OF THE CLONES, PART I

Tue, 5 Jun 2012 08:20:47 -0400

By Gary Costanza

Love ‘em or hate ‘em, you can’t ignore them any longer.

The replacement utility motors coming from China have caught not only the karting world by storm but have also found a home in custom minibikes, minibike drag racing, sailplanes, backyard race tracks, alky burning bar stools, speed boats, and any other project one can dream of building. Rumor has it that, on occasion, one even finds its way onto a cement mixer or log splitter, which just happens to be their intended use. You get 6.5 horsepower governed to 3900 rpm, low oil shut off, gas tank, air filter, and they’re ready to run with some gas and oil, for 99 bucks. And if that isn’t enough, some come with a warranty. When was the last time you bought a race engine with a warranty? Well, maybe it’s not a racing engine yet, but it doesn’t take much effort to get the clones ready.

Today’s clones are far more than just a cheap OHV utility motor. With dual main bearings, steel sleeves, forged cranks and aluminum heads, the potential for more power was too tempting for backyard and garage mechanics to resist. Until its introduction in the late 1980’s, there were very few economical alternatives to replacement motors in the power driven industry. Briggs and Stratton, along with Honda, dominated the replacement motor market with Kohler, Yamaha and others playing smaller parts. The timing was right and, with a price tag under $100, it was simply too irresistible not to give the clones a try. It wouldn’t take long for the karting industry to jump onboard, increasing the demand and versatility. It’s simple and reliable design made it perfect for even the newbie’s wrenching ability. What father could resist being a mechanical hero and crew chief in their sons, or daughters’ eyes at the local dirt track? And seeing the smiles on your kids faces when they jump on that minibike or compete in and win their first kart race is priceless.

The cost of kart racing has gone through the roof, and most would say this insane clone craze has come at the right time. Looking back at the last decade, I don’t believe anybody saw this coming at first. The major advantage of the clones is cost first and foremost. How about a complete parts inventory all for $99. These motors make rebuilds a thing of the past. A complete season of racing is not uncommon with no more than an oil change, clean air filter, and keeping up with loose nuts and bolts. And if wrenching and modifying is your passion, there are plenty of manufactures and suppliers that can fill your “stock appearing” or “open racing” needs with cams, roller rockers, stroker cranks, racing pistons, bigger carbs, stainless valves and a huge selection of billet parts. The major disadvantage for us racers would be the casted flywheel. Rated to 3900 rpms they can explode at levels above 5500. Kart racers realized years ago of the dangers of exploding flywheels. They can be lethal. But not to worry because company’s like ARC Racing and Raceseng have come to the rescue with billet aluminum flywheels that can safely take you to 9000 rpm’s and beyond.

Good or bad, you can’t help but get caught up in this growing frenzy that has brought back the entire family to kart racing. Not since the 70’s and the introduction of the Yamaha KT100, have I seen so much excitement about a new motor. The escalating cost of this sport has excluded many who, if given a chance, would love to have the opportunity to race. Having built a few Mac’s, Yamaha’s and Briggs in my day, I found myself torn between loyalty and just plain economics. So, casting my feelings aside like a good unbiased engine builder, I purchased my first Wren 5.5 horsepower clone at Pep Boys. It was red and that was 15 years ago. So, for well over a decade these clones have become a big part of my racing career.

In the late 90’s along with a few of my racing buddies we started using these imports in our backyards on tracks we built ourselves. Well, that grew and got out of hand when 4 old dads became 12 bumper pushing, rubbing-is-racing, ex stock car drivers. Then the neighbors starting coming over to watch; then we had a barbeque every race; and then we had rules. Then the police started showing up to keep the peace, but they just couldn’t help themselves and had to give it a go. Then we had a bigger track with no neighbors or police, and then we had lights and now we are a complete club that put on shows at many tracks.

This story has been repeated throughout, not only the United States, but also many parts of the world. Organizations like AKRA have jump on board with rules and national events giving birth to “Big Money” for the winners. U.S. manufactures and producers have come forth with all kinds of modified parts so you can race 6.5 horsepower at 3900 rpm’s on gas or 20 plus horsepower alky burning, 9000 rpm screaming torque monsters. From the dirt trackers of the south and northeast to the streets of LA and everywhere in between, many are finding a use for these little “diamonds in the rough.”

Clones come with different names and in all different colors like red, blue, black, yellow, and white. The colors represent different foundries, importers, and manufactures and, even though most parts are interchangeable with the Honda GX160’s and GX200’s, they all differ in quality, design, and potential power output. So the question becomes, which $99.00 clone is the best for your project or type of racing? It’s time we have them battle it out on a dyno and see what numbers best suit your needs. In order to do this, they will need to get a slight makeover before they face the instrument of horsepower truth. Each motor has had the governor removed, a new air filter, open exhaust, and main jetting change. I used a #85 main jet (box stock is usually #72) to correct for the better breathing. The open exhaust system was needed for my gas analyzer sensor. Also, these clones come with a cast flywheel and are rated to 3900 rpms from the manufactures so, even though we are going beyond that, I will stop the run as soon as power starts dropping off in order to keep things safe. Anyone who has seen an exploding flywheel knows what I’m talking about.

The first clone to face Dr. Dyno I purchased for $99 from Harbor Freight in New York. Weighing in at 28.4 lbs and 196cc, it’s blue and called “The Greyhound.” I would say this is the most popular of the clones. Every Harbor Freight across the country sells them. After a 30 minute break-in and facelift, our first contestant was ready to face the “Truth Giver.” The dreaded Dr. Dyno.

After a slow warm up to 275 degrees head temperature, the Greyhound produced 8.77hp at 4500rpm ungoverned and maximum torque was about 11.5 ft. lbs. at 2800 rpms. The air/fuel ratio leaned out a bit in the beginning, around 1000 rpms to 16. In this range the Titan clutch was still slipping. The clutch was set with a stall speed of 2500 rpms. That would be expected with a carburetor that doesn’t have an accelerator pump. It smoothed out in the 15 range and leaned out again at the end of the run around 4200 rpms as the power dropped off. This motor comes with a Ruiing carb and the results suggest it ran lean with the #85 jet. I would think that with a #88 or #90 main jet it would do better. Power started dropping off at 4500 rpms and torque equaled horsepower at 5200 rpms. With improved breathing and the jet change, the Greyhound produced over 2 horsepower more than manufacturer’s suggested rating, and produced 1300 more rpms at top end. Head temperature remained steady between 275 and 300 degrees.

In summary, the Harbor Freight Greyhound performed very well within its manufacture’s suggested range and handled even more without failure. The manufacture states 6.5 horsepower at 3600rpm. Our test motor, with the exhaust and carb modifications, did better, producing almost 8 horsepower at 3600 rpms. Not bad for a utility replacement engine.

Our next contender, from ARC Racing out of Albany, GA, cost $99.00 and weighs in at 27.8 lbs. It’s yellow and called the Dupor. It comes needing some assembly and does not have a gas tank, exhaust system, or air filter. Like the Greyhound, it comes with a Ruiing carb. It does not have a low oil sensor. The lack of these parts would explain the difference in weights. This clone appeared to be more versatile for the racing crowd, but not so much for utility replacement. The same jet change, exhaust, and air filter were installed for this Dyno test.

After a 30 minute break-in and cool down, the motor was ready for its bout with Dr. Dyno. Again, with a warm up to 275 degrees head temperature, it remained within 25 degrees during the test. The Dupor made 8.78 horsepower at 4700 rpms and maximum torque of about 12 ft. lbs. was achieved at 3300 rpms. The air/fuel ratio was about the same as the Greyhound showing a lean condition through most of the run in the range of 15. Like the Greyhound, it also leaned out more as the horsepower dropped off at 4700 rpms. Since they both have Ruiing carbs this should come as no surprise. Horsepower equaled torque at 5300 rpms. The Dupor seemed to have a slight advantage in early torque, but the horsepower curve was almost identical to the Greyhound throughout the run. The Greyhound horsepower did drop off sooner in the 4600 rpm range giving another slight advantage to the Dupor.

In summary, the Dupor performed very well and held up without failure. It appeared that the Dupor has a slight advantage over the Greyhound with respect to early and maximum torque but the horsepower curve was too close to call. In all fairness, one must consider some error factors in the data of the different runs to come to an accurate conclusion.

There is another popular yellow clone that’s imported by Jimmy Simms out of Jennings, Florida called the Ducor. At the time of this article, it too was $99. Unlike the Greyhound and Dupor, the Ducor comes with a Huayi carb. This motor gave birth to what us cloners call the BSP class or Box Stock Project. Although all 3 clones in stock form qualify as a BSP, the Ducor was imported for just that reason. Chances are you won’t find this one on a cement mixer or tiller. Check with your local track rules to be sure which clone is allowed. Like the Dupor, the Ducor, or as us cloners call it “The Duke,” doesn’t come with a gas tank, air filter, low oil sensor or exhaust system. The Duke also weighs in at 27.8lbs.

After the makeover and a 30 minute break in and cool down, the Duke was ready for its face off with Dr. Dyno. A 275 degree head temperature was achieved and like the Greyhound and Dupor remained within 25 degrees throughout the run. The Ducor made 9.18 horsepower at 3800 rpms with maximum torque of slightly over 13 ft. lbs. at 2800 rpms. Like the Greyhound and Dupor, the air/fuel ratio remained steady in the beginning but richened up after 2100 rpms and fell below 15 into the 14 range as maximum horsepower was achieved. Unlike the Greyhound and Dupor’s Ruiing carb the Ducor’s Huayi carb actually richened even further to 13 as power dropped off.

In summary, the Ducor seems to have an advantage with the Huayi carb. The extra torque and horsepower came in early and stayed ahead of the Greyhound and Dupor throughout the entire run as did the richer fuel mixture.

In conclusion, the blue Greyhound, yellow Dupor and yellow Ducor all ran without failure well past their manufactured suggested limits. Ungoverned and with better breathing, all surpassed manufactures stated horsepower and torque ratings. The Ducor’s extra power appeared to be attributed to the richer settings of the Huayi carb compared to the Huiing of the Greyhound and Dupor.

It’s easy to see why so many racers have started using clones to satisfy their racing sweet tooth. With some very inexpensive modifications to improve breathing today’s clones can achieve 9 to 10 reliable horsepower with gobs of torque which is a perfect combination for short track racing. I highly recommend adding a certified billet flywheel for safety, and it would appear that most organizations are heading in this direction. Whether you’re a newbie to kart racing, on a budget or just want to have some family fun. Today clones may be just what you’re looking for.

YOUR TRANSPONDER IS SPEAKING TO YOU

Tue, 5 Jun 2012 08:12:20 -0400

Are You Listening?
By Mike Unger

A few years ago I wrote a piece on transponders and the information it had to offer. It has been something that drivers and crew members have asked me about ever since, so I thought it might be a good time to review that information and update it as necessary.

As you know gathering data is a very important part of racing. I recently heard a great saying that I kind of live by, ‘In God we Trust, everyone else needs data.’ Data gives me clues to all that goes on with the world. Without data, I am lost. I take close notes of everything that goes on with the kart. I use some of the best data acquisition on the market. I have a weather station and I am constantly looking for more data to find that elusive .2 secs that I need to win.

Well just when I thought I had all the data I needed, I found a brand new source that has been around for some time. I just never looked into it; my transponder. That transponder that I bought a couple years ago is a great source for data and recently, I was surprised how much I can learn from it. The source of this new data is www.mylaps.com. This site is dedicated to all AMB transponder users, and is available for you to review as long as your race series submits the info from your race you can look up all the laptimes from all the races you’ve ever entered, and much more.

This is how it works. First you purchase you own personal AMB transponder. Most of today’s race series require transponders for scoring, so a lot of us already have them. That transponder you have is unique to you, as it has your own personal frequency. Your race series uses it to identify when you cross the start finish line in order to keep track of your track position. The transponder system records your laptimes, as well as all of your competitors lap times too. At the end of the race day your race series can post all of the results on www.mylaps.com for you and everyone else to see.

Now this is where it gets interesting. On their website you can register your own personal transponder number, team name, sponsor and even a picture for free. This is the first step in unlocking some of the most interesting data you will find. What you can do after you register is go to ‘my results’. Here you will find every race that your transponder has ever been in. It doesn’t matter when or where as long as the race series posted the results. So, if you select one of the races you can pull out your finish position, lap times and most importantly the laptimes of everyone else that you raced against. This is where you can really learn something. You now can compare your times to everyone else that was in your race and therefore learn a great deal.

Let’s take the obvious first. If you finished 7th you can compare your laptimes to the winner and get some idea of how much faster he or she was than you. But, just looking at one single fast lap does not tell the whole story. When you compare your laps to the winners, you not only can see how much faster they were, but also at what lap or laps they were quicker. Next, look at those racers who finished right around you. Were they faster than you at the beginning of the race and you got a little better or vice versa?

Let’s look at what I learned from an event I attended at New Castle Raceway Park a while ago. First of all, let me say that I raced in the G1 class, which was the 125cc shifters with drivers 35 years and older, although that is somewhat irrelevant to this article as I’m discussing learning from what your transponder is telling you, more than any personal information.

I ran well, but finished ahead of mid-pack. Not bad, but I know I could have done better and was confused as to why I was off the pace. I decided to take another hard look at my laptimes to see if anything was obvious.

Looking at my lap times for both races I noticed that I ran my best laptimes toward the end of the race. In the 10 lap Prefinal, I ran my fast lap on lap 9 and in the 16 lap Feature I ran my best on lap 13. Just looking at that trend tells me that my new kart tuned the way that it was, ran best at the end of the run. Looking at my post race notes, (you do take notes don’t you?), I see that I complained that the kart didn’t have much grip at the start but then came in at the end of the session. This is supported in the laptime data also. But of course, other things could have done it too, the sun came out, the track got faster, etc. By comparing my laptimes to the racers laptimes that finished around me, it shows an interesting trend. It all shows that they were faster than me at the beginning of the run but I was faster than them toward the end. Looking closely at the data shows that in some cases I was giving up nearly a second per lap at the beginning of the run. Then after my kart came in I was running nearly 0.750 seconds faster on a lap by lap basis. Unfortunately for me I had given up too much time at the beginning of the race to make up for it at the end.

What did this tell me and how will I use it in the future? Well, first of all it tells me that I need to tune my kart a little differently than I did for that particular day and conditions. My previous kart was a Biesse SGM. That kart and tire combination was extremely quick early in the race and then tended to understeer or tighten up as the race went on. The Kosmic TM kart that I ran in this race using the same tire appeared to be exactly the opposite. It lacked a bit of grip at the beginning but then came in nicely toward the end of the race. This is an important thing to note in how I will go about tuning that kart in the future.

Since my laptimes continued to get faster throughout the run I don’t think I ever reached my peak laptime in the race. From looking at the data and reading my post race comments the chassis was setup too loose at the start of the run. Again, this was my mistake because I was tuning my new Kosmic like I had always tuned my Biesse. Now that I have seen this I will setup it up to come in a little earlier in the run.

OK, I learned that my new kart is different than my old kart and I need to adjust my tuning and driving style to it. What else did I learn from my transponder? Well again looking at all of the data and comparing my laptimes to those that finished in front of me I learned that in the races I was generally faster than the racers even 2 or 3 positions ahead of me. What does this mean? This means 2 things. I need to qualify better and that comes down to tuning the setup of the kart and improving handling. While my previous kart was very quick right away and was great for qualifying, my new kart needed more thought put into the setup for qualifying. Now that I know that I have the speed on longer runs I need to work on a setup for short runs.

Assuming that my driving style hadn’t changed much from the beginning of the race to the end, the only thing that could have changed was my tires. So spending some additional time getting to know how they react to varying track conditions is what I need to focus on in order to improve my times at the beginning of the race.

That of course can mean I need to look at ways to tune the chassis to allow those tires to work better as well. That really comes down to spending more quality time during my testing laps either prior to qualifying or during the day before. While I was turning 400 laps learning the track, setting up the engine, etc., I need to allocate enough time to run enough laps that would simulate the start of the race so I would know when the kart and tire combination would begin to work its best, then start to tweak until it ran more consistent time from the start to the finish.

Often times I think drivers forget about that…I know I did. Most set their karts up to run as fast as they can, but what they neglected to learn was how it reacts throughout the entire course of an event. They might be blazing out of the gates, but end up finishing off the pace due to the fact that they wore out their tires.

The other thing I learned was that I need to work on my race craft a little bit more. Last year I only raced 4 complete races and the lack of race craft showed in the first race. The only way to cure this is to race as often as possible.

As you can see I learned a lot from my transponder. I learned that I need to setup my new kart much differently than my old one. I learned that I need to do some testing to find out a good 2-3 lap qualifying setup, and a need to race more. Having pointed out those 3 things to improve on could apply to any racer in the world.

Data is knowledge; It’s just knowing how to use it that can make the difference.

MAXIMIZING RELIABILITY

Tue, 5 Jun 2012 07:57:15 -0400

Through Basic Preventative Steps
By Mike Unger

I was at my first trip to Daytona for the WKA Manufacturers Cup this past winter and as I was getting my son though the scales and past tech I heard someone say “I think someone should write an article about how to properly prepare a kart.” Being a technical writer I am always open for new article ideas, so here it is. I can’t remember who actually said it but thanks for the suggestion.

The first thing to remember about prepping a kart is that there is more to it than just getting through safety tech. Safety tech, while extremely important and required by all sanctioning bodies, is only half of the work that needs to be done. There are a number of things you need to do to your kart to not only be safe but also to be as competitive as possible. A kart that only passes safety tech won’t be ready for the big race. You need to consider everything from the brake fluid to the numbers on the side of the sidepods. Just for simplicity let’s start at the front of the kart and work backward. I will cover everything from safety tech to common sense as well as some tips I have picked up though the years.

So starting from the very front of the kart let’s considering the nose and bumper. For those of you using CIK style bodywork (WKA Manufactures’ Cup Style) you have six pieces to keep an eye on. The plastic nose piece, the lower bumper bar, the upper bumper bar, the red plastic part than connects the two, and the two clamps that pull it all together. Check the plastic nose piece for cracks and tears especially around where the nose piece and metal bumper bars attach. Often cracks or tears appear here from excessive use. Replace if necessary. Check the bolts that attach the bumper bars to the frame. Make sure they are tight. If the nylon nuts are easy to turn from being on and off often replace them. If applicable, check that plastic piece that connects the two bumper bars. It has two bolts in it as well. Make sure those are still tight. Finally check the clamps that pinch the plastic nose around the steel bumper bars. Make sure these are tight and apply enough tension to keep from popping off. WKA says these quick release clamps are optional and you can bolt on the bumper if you like. I suggest using the quick release type and simply use a plastic wire tie to keep the clamps from popping open. If you are not using a CIK style front bumper you still need to look at the attachment points and make sure they are all tight. Nylon locking nuts are a must for all of these points as well. Remember for most sanctioning bodies nowadays losing the front bumper will get you black-flagged.

Now let’s consider the accel and brake pedals. Where these pedals attach to the frame it is required that the bolts be safety wired or pinned with cotter keys or similar. Check these bolts to make sure they are not excessively worn as they do provide the pivot for the pedals. Replace if necessary. Also check the nuts and make sure they are tight but not tight enough that it causes the pedals to bind because this can result in a stuck throttle or hanging brake. Make sure to clean this area from time to time as dirt and sand can get in there and cause parts to wear excessively. Also check the attachment of the brake rod and brake cable to the pedal. Make sure these attachments are safety wired or safety clipped as your chassis manufacturer designed. On the accelerator side if you are attaching the throttle pedal to the cable with a simple loop I suggest some kind of protection to keep the thin cable from rubbing against the metal pedal. I use a piece of plastic brake line or fuel line to protect the cable. Inspect the cable regularly, every year I see 3 or 4 karts sitting on the side of the track with broken cables. If you are using a metal rod at the throttle pedal check that attachment point as well. I suggest safety wiring that bolt also. While it is not required for safety tech it is a good idea.

Moving farther rearward now let’s consider the steering. First where it attaches to the frame at its front most point. Likely the steering shaft goes through a bracket in the frame, through a bushing and secured with a nylon bolt. An E type clip or safety wire on the end of the shaft is required by safety tech. Check to make sure that clip is still there and is tight. I have seen these vibrate loose and come off. Also check that bearing or bushing the steering shaft sits in. This bearing is attached to the frame with an internal C clip (snap-ring). Check for excessive wear on this bearing. An excessively worn bearing will effect wheel alignment and steering, replace if necessary. Moving up the steering shaft, look at the pivot that the steering shaft passes through and connects to the frame uprights. This is usually a plastic bushing block with a through bolt in it. Check that the plastic is not cracked or worn excessively. There should be very little movement between the shaft and the plastic bushing. If there is replace it as it can effect alignment and steering feeling. The bolt that attaches the plastic bushing to the frame uprights need be safety wired or clipped for safety tech as well.

Now let’s talk about the steering wheel. It may sound simple enough and is easy to overlook but a couple things need to be considered here. First is it worn and slippery to your driver? Often over time the leather or suede material gets matted down and too slippery to get a good grip on. Also inspect the spokes. Over time they can develop cracks and eventually break. Replace as needed. Next look at where the steering wheel attaches to the steering shaft. This is usually an aluminum hub. You need to make sure all of these bolts are tight and at least 3 of them are safety wired or clipped. Also inspect the bolt that attaches the steering hub to the steering shaft. This one for some reason always seems to vibrate loose. I recommend replacing that nut and bolt often. Also make sure that bolt is safety wired as well; double nut if possible to further reduce the chances of it loosening. Look at your gauge attachment to the steering wheel. Is it tight? Is the wiring frayed or is rubbing on an edge of a bracket that can eventually cause a problem? If so reroute and replace as needed.

Let’s move to the middle of the steering shaft and the tie rods and tie rod ends. The ties rod ends need to be connected to the steering shaft with a bolt, nylon lock nut and safety wired or clipped. Inspect the tie rods and tie rod ends. Sometimes in the heat of battle you might not notice a bent tie rod or end. If you use a throttle cable all the way to the pedal, look where the tie rod and the throttle cable cross. Sometimes the throttle cable will rub on the tie rod and cause excessive wear. You also might consider rerouting the throttle cable to avoid that in the future. There are a number of kits available to relocate the cable and generally cheaper that a tie rod plus you buy piece of mind. Moving outboard to the spindles look at where the outermost tire rod end connects to the spindle arm. These bolts need to be tight and safety wired as well. Also inspect the spindles for bearing wear. Bearings that need replaced will allow the spindle to move slightly relative to the frame. The kingpins (the long bolt that connects the spindle to the frame) can use inspection as well. They tend to wear a little over time and in the event of hard contact can even bend. A bent kingpin can affect caster, camber and toe. Look these over closely and especially after an incident.

The fuel tank while a seemingly simple part can be a problem should it leak or come loose. Inspect the fuel lines for places where they could rub and eventually leak. Also pull the inlet line out of the tank from time to time and check the line. Over time it gets stiff, can crack, and will stop moving around in the tank. This will lead to fuel starvation in the corners and could damage your engine. Also put zip ties on all fuel line connections as they are required for safety tech. Also here is a good tip I picked up looking at karts on the grid. If you are using one of the quick removal type fuel tanks with the big plastic three spoked wing nut attach a zip tie to the frame and zip tie in a way that won’t allow that nut to loosen. Trying to keep the fuel tank in the kart with your knees while trying to race isn’t too fun or easy.

Moving to the sidepods now, these parts play an important role in protecting you from a side impact. They also will get you black flagged should they fall off. So for that reason check the connections often for tightness and replace the nylon locking nuts too. Since we remove the sidepods often to get better access to the engine and frame those nuts tend to wear out. I replace the 6mm Allen bolts with a simple pin and clip unit you can buy at any hardware store. It makes for easy removal of the sidepods yet provides a good strong attachment method. Just be sure to get a good thick clip and inspect those often as well.

Sticking with the frame part of the equation for now let’s consider the seat. Of course everyone knows it’s important it is neglected more often than any other part on a kart. The stiffness of the seat has a big influence on how the kart handles. If your seat is cracked, bottom blown out of it, or in general in very bad state of repair it is affecting the performance of your kart as well as a concern for your safety. Replace your seat if it has cracks or seems flimsy from too many years of racing. Also check each and every attachment point to make sure the seat bolts and seat struts have not loosened up over time. As frame flexes, the seat does too.

If you are like most karters you attach your lead ballast to the seat. Be sure to use 5/16in bolts for every 5 lbs of weight, and if the weight weighs more than 5 lbs two 5/16in bolts are required. Double nuts or safety wiring is required of all ballast and in the case of the WKA all ballast of required to be painted white.

Let’s talk about brakes now. Brakes are one of the things that you simply cannot neglect on your kart. You need to inspect them often and replace and repair as needed. You should only be able to push your brake pedal ½ way through its total stroke before it stops because the pads engage the disk. At that point the pedal feeling should be very stiff and not spongy or mushy. If the pedal stroke is too long it’s time to replace the brake pads. Follow your manufactures’ recommendations on how to replace and what pads to use. Often your manufacturer has a number of compounds of brake pads to suit your driving style. So while you are replacing them, get your kart dealer on the phone and see if there is something out there that can help you brake better. Look over the brake lines as well. Finally, look for signs of abrasion, leaks, and loose fittings. Do not take chances here. Replace anything that is questionable with a new part.

If the brake pedal doesn’t get firm after the pads contact the brake rotor the system needs to be bled. Again you need to contact your manufacturer and find out what kind of brake fluid is used in the system. There are a number of types of fluid, (DOT3, DOT4, DOT5 and so on) but they are not compatible with each other. Putting the wrong kind in your system can render it useless and dangerous. After you have identified what fluid to use you will need a brake bleeder and a couple wrenches.

There are a couple ways to bleed the brakes; I use the traditional kart gravity method. You will need a brake bleeder. It is simply a jig that screws into the master cylinder with an upright that elevates the brake fluid so it is the highest part of the system. Once the bleeder is screwed into place, loosen the cap on top of the reservoir and turn the valve open on the bleeder. Now your system is ready to be bled. Find the bleeder screws on the brake calipers. These usually come in 2 types. One is simply a small allen bolt that you remove and let the brake fluid flow out of. The other is a valve like automobiles use. The allen bolt usually makes a mess but it’s effective. The automotive type is an actual valve with a hole in it. To avoid the mess you can put fuel line over the end of the valve and drain the excess fluid into a container. Allow the caliper to bleed until the fluid is clean and doesn’t contain any air bubbles.

After you are satisfied the old fluid has been replaced and no air bubbles are present replace the Allen bolt or tighten the automotive style valve. Now close the valve on the brake bleeder, remove, and replace the bolt or cap on the master cylinder. Repeat for the other side of the caliper and other brake systems as needed. I recommend bleeding your brakes 2-3 times per year whether the brakes need it or not. Brake fluid tends to absorb water and keeping fresh fluid in the system is a good thing. Also brake fluid is very corrosive on paint and is not good for you to come in contact with it either. Use rubber gloves and clean your kart and your hands thoroughly after you are done.

Now we move on to the rear of the kart. Here is where you will find all of the dirt, grease and oil from the engine, chain, exhaust and the track. It’s important to keep your bearings and chain lubed but all of that lube also attracts dirt. That dirt gets into bearings and chains and in general will increase the rolling resistance and slow you down. Not to mention it will cause bearings and chains to wear out more quickly causing you to spend more money in the end. The only way around this it to keep the rear of the kart meticulously clean. One of the new pieces I have found that make this mundane job easier is the new Tillet chain guard. This chain guard encloses the sprocket on three sides helping to contain all of the lube from the chain. Containing all of that mess helps keep it off of everything else and keeps it from picking up dirt and grime that will eventually grind into your bearings.

Once a year I recommend taking your rear axle completely out of your kart, removing the bearing cassettes and thoroughly cleaning them. Check your bearings for excessive play, if they do replace them with new. If they do not have excessive play simply clean them, and re-lube them. Many racers pop the bearing shields off and flush the bearings with solvent to get them cleaned but in many cases that can cause problems as well. Often getting the shields to go back in place is a challenging task. Putting a bearing in the rear axles without a bearing shield will certainly cause you to replace that bearing sooner than later. So I recommend wiping the bearing off with the shield in place, carefully paying attention to the grime around the shield and then re-lubing with a quality lube. If the bearings still sound like a coffee grinder after this go ahead and try to flush the bearing out by popping the shields off. Clean, re-lube and re-install as before just pay attention to that bearing shield throughout the season as it is likely to pop off.

The bearing cassettes and bearing interaction is something that should not be overlooked as well. The bearing should fit snuggly inside the cassette yet should rotate relative to the cassettes without much effort. If it does not it needs to be cleaned out and polished up until it does. When you put the bearing back in the cassette I recommend using a small amount of anti-seize grease to keep things free. Before you put everything back together this would be a great time to replace those bolts that are stripped out or looking kind of bad with new ones. Also don’t forget to use blue Loctite on every bolt. You can’t afford to have a bolt come loose in a race.

That pretty much is it for the chassis stuff. Engine stuff is largely dependent on what kind of engine you have but things to inspect and rebuild are fairly standard. Clutches need to be inspected and rebuilt as needed. Broken exhaust springs need replaced and exhaust pipes need to be properly secured. Carburetor diaphragms should be replaced once per month at least, and the chain and sprockets need inspected and replaced as needed. When in doubt replace it. It is no fun to lose a race because you tried to get one more race out of that consumable part.

So there you have it from the front to the back, go over the whole kart and be 100% ready on raceday. If you take care of those maintenance items now you will get though safety tech quickly, and instead of fixing your kart between heats you can work on making it faster.

FREE IT UP

Tue, 5 Jun 2012 07:56:36 -0400

When Too Much Grip Is A Problem
By Mike Unger

Have you ever been at the races on a really hot day with a lot of karts to race against? Ever try to deal with too much grip? Yes, that’s right too much grip. It shows up as understeer or push and it happens more often than you think. On the regional and national level, it happens quite often and even at the club level, when there are a lot of karts on the track and the conditions are right, you can have more grip than you know what to do with. Dealing with it is not as simple at you might think, but I will try to give you some pointers to help free it up.

First, this situation is somewhat inherent to the design of karts. Most of all it stems from the solid rear axle which defines a racing kart. In order to make a kart turn you need to unload the inside rear tire so the front tires can steer the kart. If you don’t unload that inside rear tire the 2 rear tires that are linked together with the axle simply overpower the fronts and push the kart forward. This is the fundamental story of a kart. It inherently has a tendency to understeer. The more grip you have the more the tendency is.
So what do you do without it? You need to find ways to unload that inside rear tire. Of course like everything there are multiple ways to do that. Since the problem originates at the rear I recommend to start there first. These are the things I would try in order of severity. That is, the first on the list is the smallest change and the last is the biggest change. You will need to choose what is best for your kart by doing some experimenting.

1. Loosen the rear horizontal bar at the rear bumper. Don’t remove it as that would be against the safety rules, but simply loosen the nuts holding it on so that you can wiggle it a bit. This will reduce the stiffness of the rear frame and allow the rear to flex more helping that inside rear tire to unload more.

2. Remove the rear torsion bar and side bar if installed. Again same as #1 we are trying to get more flex in the rear of the kart.

3. Widen the rear track out as much as possible. This change will reduce the amount of weight on the inside rear tire giving it a better chance of unloading.

4. Change to shorter rear hubs. The idea here is to allow the rear of the chassis to flex more. The axle is part of the stiffness of the frame and the longer wheel hubs just add to the stiffness of the axle. Putting shorter hubs on will allow the axle to flex more.

5. Unbolt the 3rd bearing. The idea is to again allow the rear of the kart to flex more. By loosening the 3rd bearing support you take the inside frame rail out of the equation and the chassis will flex more. When you do this you don’t need to remove the bolts completely. Just loosen the nuts and bolts until the cassette can wiggle relative to the bearing hanger. If your kart design does not have bolts that go through the cassette with nylon locknuts you can use zip ties to hold the cassette in place. Note: Be very careful when doing this one. The axle will flex more and the possibility of popping a chain becomes greater. Chain adjustment may be necessary. Also you need to make sure you secure the cassette parts. You don’t want the cassette to spin and get caught in something.

6. Finally change to a softer axle. This is the most drastic change and one of the most difficult to do quickly at the track. After some experience with a lot of grip, you might consider doing this one first. It is easier to add more grip to the kart than take it away.

What happens if you have made all of those changes and you still can’t seem to get the kart to turn?

If you still can’t get the kart freed up, work on the front. When working on the front you are still trying to free up the rear, but you do it in the opposite way you did in the rear. In the front you will need to add grip. Adding grip in the front to an under steering kart will give the front tires a better chance of steering those 2 big rear tires. Again like the previous list these are listed in order of smallest to biggest effect.

1. Add front torsion bar. Unlike in the rear when we were trying to add flex and therefore decrease grip here we are doing the opposite. By adding the front bar we increase stiffness to the frame, decreasing the front end flex and therefore make the castor that is designed into the frame more effective. This will cause more weight to be transferred off of that inside rear tire helping it to slip.

2. Increase front track. Again the game here is to increase front grip. Increasing front track will make the front end more sensitive to the castor designed into your frame giving the front end more leverage to unload the rear inside tire. Be aware making this change will improve turn in performance but will decrease mid corner grip. This is because moving the tires are further away from the center of the chassis there is less weight on those tires in a turn.

3. Increase castor. This is the most effective way to add grip to the front end. Adding castor will increase the front ends ability to lift that inside rear tire and therefore allow the kart to turn. Of course the negative here is that steering effort will go up causing arm fatigue.
Finally one of the most effective ways to reduce grip when there is a lot of rubber is to decrease tire pressure. Lower tire pressure will allow the tire to run cooler and therefore will have less grip. Be careful not to reduce tires below the tire manufacturers’ recommendations. Too low a pressure will be a safety concern potentially resulting in de-beading a tire.

Of course with all of the changes listed you might find a combination that your kart will not respond favorably to. The response usually shows up as a bad mid corner hop. This still is happening because there is too much grip but the hop occurs because the frame is flexing a lot because the tires have so much power and won’t release from the track. The frame winds up and snaps back into shape resulting in a hop. Common ways to fix this is to change the frame stiffness is some way. Sometimes adding or removing a torsion bar helps get rid of the hop, usually removing helps more often than not though. You also might try to remove seat struts, but in my experience this isn’t always effective.

Now you know what changes to make to the chassis to free it up when you are dealing with a lot of rubber. A lot can be done to help the kart get around the corners. Smoothness is key to going fast when there is a great deal of rubber. The more abrupt you are with the controls, the more likely the chassis will hop and bind up. Be smooth with the accelerator pedal, brakes and steering. Try changing your driving line. You will likely find that moving your line just a few inches closer to the center of the turn or farther away will help free the kart up. Finally try a bit more trail braking entering the turn. Carrying the brake into the corner while you turn the steering will be asking the rear tires to both turn and slow the kart. If you have too much grip, in the beginning, this will be asking the rear tire to do too much work causing them to slide helping you to turn. Of course trail braking is quite an advanced technique and requires considerable practice to get it right. During one of your normal testing days you might want to consider spending time learning the skill. It could come in handy someday.

So on that really sticky summer day at the track when the rubber is so thick that you can’t get the kart around the corner do the following. Remove as much grip from the rear as you can and then if that is not enough add grip to the front. Be smooth and use that trail braking skill you have been working on. With a little bit of practice and these simple guidelines, you might end up in the winner’s circle.

RACE DAY, PART II

Mon, 4 Jun 2012 10:03:01 -0400

Preparing For Your First Race
By Mike Unger

This is the second part of a series of articles that will take you through the entire race day.

In the first article I took you through getting in the gate, safety tech, registration and practice sessions. The article not only explained what to expect, but also gave some suggestions to make your race day more successful. How to prepare for each session and goals for each session were outlined. Now you are registered for the race, have been on the track through two successful practice sessions and are now ready to hit the track and see how all of these preparations pan out against other karters.

After the last practice session is the time to start thinking about race setup and how you will plan to attack the racing portion of the day. Most clubs’ use one of two types of race format. The first is called pea pill or random draw. When you register you will draw a pill with a number on it or the scoring computer will randomly assign you a number. This number will determine your starting position for the first heat. For the second heat the starting grid will be inverted, giving everyone a fair shot. Then the starting position for the feature will be determined by your finishing order in the first two heats. This kind of racing is very popular at the club levels because it forces everyone, no matter how good they are, to learn how to pass and be passed. You might find a fast guy randomly on the pole for the first race but then for the second race he or she will need to come up through the pack in order to get a good position for the feature. For these kinds of races you need to have a simple and smart strategy.

The first thing you need to realize is that in order to get a good starting position for the main you need to finish both heats. That means you need to stay out of trouble and not take too many chances trying to overtake your opponent. If you end up in the grass for even one of these heats your starting position in the feature will be at the back of the pack. The simple and smart strategy for this kind of race format is to be a little conservative and try to get up to at least the top half of the field in both heats. If you do that you will be sure to have a good starting position for the feature race.

The second kind of race format is the qualifying format. The first round of racing will be qualifying. If you have never qualified before, it is a very straightforward. The grid worker will space each racer out with enough space between as to make it more likely that you will not catch the kart in front of you. You run three or so ‘hot’ laps and your fastest time of those three will count as your qualifying lap. After qualifying the Pre-Final is run. The starting position for this race is based on qualifying, fastest kart on pole slowest kart on the tail. For the ‘Final’ the karts will be gridded based on the finishing position in the Pre Final. This format requires a more aggressive approach than the pea pill format since pushing the kart to its limits is required at each stage to get into a good position for the Final.

Now that you understand the race format and you have a strategy for the racing it is time to start thinking about a race setup. In the first article we had a strategy in practice. That was to work toward a setup that would be a little loose (or oversteer prone) on the last lap of the last practice session. It was also a strategy to pay attention to how many laps of hard running it took for the kart to ‘come in’ and become more drivable and therefore fast. Well this is where we need to take that information and put it to use. At this point of the day there are basically two different race setups, one for qualifying and one for the actual race. If you are running the pea pill type of format you don’t need to worry about the qualifying setup since you will be going right into a race.

To setup for a race session you need some pieces of information. You need a good understanding of how many laps in your practice session it took for the kart to come in and be quick. You also need to make an educated guess on how much more grip the track will have when you race again compared to your last practice session. This information will greatly help you determine the best setup for the first race. For the heat races you need a kart that will come in and be fast before you get to the halfway point of the race. That means you need to take the setup you had for the last practice and reflect on it. Was the kart fast on lap 2 or lap 6? If the kart was fast on lap 2 in practice you probably have a setup that is too tight for a 10 lap race and need to adjust accordingly. If it was fast on lap 6 in practice you are likely in very good shape. For details on what adjustments to do and when I suggest you visit www.nkn.com and under the ‘How to’ section lookup the articles ‘Rear End Adjustment’ and ‘Front End Adjustment’.

Also throughout the race day the track will be changing and you will need to be aware. If it has been two hours since your last time on track and you are the 6th race of the first round of races you can expect the track to have significantly more grip that it did in practice. This will cause the kart to come in more quickly and be more prone to understeer on longer runs. If the clouds have come in and the track has cooled off the track will have less grip that you had in practice. Either way you need to be carefully watching the conditions and anticipating how the track will be and adjust accordingly. This kind of tuning takes time and experience to get it perfect. This is why the locals that race at a given track all the time have an advantage. They know from experience what the track is going to go and by how much. The best bet is to be conservative the first heat and tune accordingly for the second heat race.

If you are racing in a qualifying format your strategy for setup needs to be a little different. You will only get 3 laps in qualifying. If your kart is setup so that it doesn’t come in till lap 6 you will never get that optimum lap. Like in the pea pill format you need to consider the grip of the track as well as how the kart was in practice. Then you need to adjust the kart to come in on the first lap. If you had the ideal practice session and at the end of a 6 or 7 lap run your kart was good, the easy and straightforward way I usually do this is under that situation is increase the tire pressure 2-3 psi. This will narrow up the contract patch a bit and force the tire to support the same load with a smaller footprint. This will heat up the tire quicker and allow you to get that fast lap in during the 3 laps of qualifying. If your kart never came in during practice you will need to consider other chassis adjustments.

After practice sessions are complete there will be a mandatory drivers meeting. In the drivers meeting they will explain details of how the races will go throughout the rest of the day. The head flagman will explain how he or she wants the starts to go, and what he expects out of the pole position driver. They will also explain how the out lap and cool down laps will go. These are details that are unique to each track and organization so it’s important for you to fully understand these details. If they do not tell you these things in the drivers meeting ask the head flagman afterwards. The last thing you need to worry about is what to expect. They will also do a random roll call. If your name is called and you are not at the drivers meeting you will have to start on the tail for the first two heats. After the drivers meeting the races will immediately start.
Immediately after the drivers meeting go back to your pit and put the setup on the kart you have been thinking about. You won’t have lots of time to do this so it’s important that you decide before the drivers meeting. Don’t forget to top off the fuel to a level high enough so when you finish the session the fuel level will be above the mark you put on the tank from practice. Check the wheel nuts, gas cap, and engine mount clamps. These are the ones that I constantly see come loose and cause problems out on track (I have made the mistake a time or two as well).

Over the PA the officials will start calling classes to the grid for the first session. In most cases they will post a lineup sheet somewhere near the grid with your grid position. This is the position you will start the race or go out for qualifying in. As a courtesy if you are at the back of the lineup wait till the other karts in front of you get in position before you do. Grids tend to be tight and busy places. A little courtesy goes a long way toward making a smoother race day.

If this is a qualifying session, you need to be totally focused on getting absolutely everything out of the kart it has to offer, without going off the track on the first lap. If you do, you will guarantee to be on the tail of the field for the PreFinal. So as a simple smart strategy I always recommend that you run the first lap a little bit conservative to get one ‘in the bank’. After you have a decent lap recorded you can push it to the limit. Even if you go off on the second lap you won’t be on the tail because you have one in the bank already.

If this session is a Heat race then remember what the situation is. There are karts all around you and some are faster than you and some are slower. You need to race smart and move up through the field without getting caught up in trouble. It is just as easy to spin off the track as the result of being too aggressive trying to pass as it is to be taken out by someone being too aggressive passing you. Remember the goal is to finish in the top half of the field each race. If someone gets alongside you let them go in the first two heats. This is not the Final race just the race to set the grid for the Final.

If this session is the Pre Final in a qualifying format the situation is a little different. The karts around you are about the same speed as you. This means you will need to look for opportunities to make clean passes and push as hard as you can without risking a spin or an off track excursion. Keep in mind though, this is still the Pre Final and spinning on the first lap will guarantee you a poor starting position in the Final. Be smart and keep your eye on the prize.

Ok, now you have worked your way through the heat races and it is Final time. You had to make setup decisions throughout the races as well as have a solid strategy to get to where you are. If you are on the pole or near the front you did a great job throughout the heat races and must be doing something right. For you the strategy is simple, keep doing what you have been doing and be smart. Do that and you are likely win. If you are starting at the back of the pack it is time for some thinking.

If you have had a good day and your current position to this point is a good performance for you then I would suggest keeping with the program and get through the day targeting where you are now or even look for an opportunity to move up a spot or two. If you are not happy with where you are and you should be more towards the front you need to try something different. Usually you have time before the Feature race to look back at your notes and figure out where you went wrong. Look at your comments after each race and try to find out where you went wrong. Did the weather change and you didn’t adjust accordingly? Did you miss the setup right from the start? Did you have mechanical problems? All of these things are factors that are easy to miss in the hustle and bustle of a race day. No matter what the reason, if you are not happy with where you are starting I suggest you make a change to your setup. Make a gear change, track width, torsion bar or some other change. You really have nothing to lose. Best case you stumble on to that half a second per lap you need, worst case you learn what your changes feel like and keep that knowledge for future situations.

So now I have taken you through the heat race portion of the day, discussed strategies and things to watch for, and covered the simple things like what info to listen for at the drivers meeting. Now all that is left is the Feature race. In the final article in the series I will go over the Feature race, tech and very important information to help you repeat the success or help you to not repeat your mistakes next time.

RACE DAY, PART I:

Mon, 4 Jun 2012 09:53:28 -0400

In the Gate and Practice
By Mike Unger

For the next series of articles I will be taking you through a complete race day. Everything from the time you show up at the front gate to leaving the track after the races are complete. I will be giving you suggestions and guidelines to make your race day go more smoothly and hopefully more successful.

The first part of the series will take you from the time you enter the track to the end of the practice sessions. I will go over the basics such as registration to setting a plan in practice so you have the best chances for success for the races.

Before you even think about entering your first race you need to make sure your kart is completely ready to go. This means your kart has all the necessary safety requirements for safety tech such as safety wired brake system, functioning brakes, and a safe steering system. In addition to the kart being safe it also needs to be completely prepared to race. This includes things like alignment, scaling, and proper baseline setup. For more details into all of that you can visit www.nkn.com under the ‘How to’ page for an article called Preparing a Kart. That article will take you from the front of the kart to the rear. Using that article as a guide you can show up at the track ready to go.

The first order of business when you come to the track is getting a pit pass. To get a pit pass you will need to sign a waiver acknowledging that you understand the risks of being in the pits and out on the race track and you accept those risks. Paying the nominal fee for the pit pass also in many cases provides insurance should you get hurt at the track. For details check with your local track owner. Most pit passes are wristbands that you will be required to wear whenever you are in the pits and out on the track. After you get the pit pass ask the worker at the gate where you can park. Often there are reserved pit spots and free pit spots. Of course reserved pit spots tend to be closer to the grid so you will have to balance your budget vs. convenience for this decision. While you are asking for directions on where to pit ask them where safety tech is since that will be there next task at hand.

After you get to your pit spot, unpack your stuff and setup your pit spot. Don’t spend too much time on pit setup right now since the line for safety tech will be forming and it will be in your best interest to get that over with as soon as possible. Get your kart on the kart stand, put your helmet and chest protector (if you are with a driver requiring one) and get going to safety tech. In safety tech the official will check out your kart to make sure it has all of the safety wired bolts, functioning brakes and numbers on all 4 sides. Your helmet will also be checked to make sure it meets current requirements. It is extremely smart to do your homework on this long before you get to the track. If your kart does not pass safety tech you will not be allowed on track. Trying to drill a bolt to safety wire it while at the track is not a trivial thing. After you pass safety tech the official will most likely put a sticker on your kart and possibly on your helmet. Before you leave safety tech ask the official where registration is as that will be your next stop.

Registration is where you will register for your class, give them your kart number, transponder number (if you have one) and pay for your class entry. If this is a WKA, IKF, SKUSA or other major sanctioning body’s race you will likely need a membership card to the organization in order to race. Check before you go to the race to see how it works. If you are not a member you can buy a 1 day membership right at the track. A one day membership will allow you to be able to race but you will need a full membership to accumulate championship points. Again something you should consider before you get there. One of the big questions I always hear from new racers is how do they decide kart numbers? In many local series it is simply first come first serve on the first race of the season. Then after that you will have to find a number that is not already taken. For regional and national competitions you can reserve your kart number for a fee for the entire season. Like the pit spot you will have to balance your budget vs. convenience on this one. Worst case with a little tape you can modify your race number temporarily or buy new numbers at the track. Before you leave registration, be sure to ask about the race day schedule. You will need to know when practice starts, what the practice order is, and what the race format is. They should be able to help you out with all of that information in registration.

OK, now that you have all of the paperwork done and all the waiting in lines is finished, it is time to get into the business of racing. From now you are in race mode and you need to be focused on preparing yourself and your kart to get the best result. I am going to assume the following things have already been done in your preparation prior to coming to the race. First your kart is fully prepared and you already have a basic setup as a starting point for this track and this time of the year. Second you have driven this track already and at least know the racing line. Finally while this may be your first race but you have done hundreds of laps in a kart and can run laptimes that will at least allow you to mix it up with the pack, maybe not the lead pack but at least with someone. If these assumptions are not true you really should not be at this point. Racing is more that about driving around a track in a kart it’s about competing with at least one other person.

Now at this point in the program you should have enough time to walk the track before official practice starts. I recommend that you always walk the track before each race day regardless if this is your first or 400th time at the track. Walking the track will give you the time to focus on today’s tasks and give you a fresh look at subtle changes in the track since your last lap around.

Starting at the beginning of turn one walk around the track turn by turn. Concentrate on what the surface of the track looks like. Is it dirty and have lots of bits of rubber on it or is clean? How does the track look off-line the passing zones? If the track is dirty on the racing line rest assured by the time it comes around to race the track will be clean but it might mean that the passing zones will remain dirty and slippery. Check for areas where karts tend to step a wheel off the track and kick dirt up on the track. Mentally note those locations as they likely will become dirty and slippery throughout the race day. Check the curbs and the exits of the corners. A new crack in the curbing or a deeper hole in the transition between the track and the grass is something you should be aware of. Part of winning is not popping a chain on the first lap because you didn’t pay attention when you walked the track. Also look at the rubber buildup on the track. Often if the track is a popular place a different series might have been there the week or even day before. More or less rubber that you are used to seeing might mean you need to be more mindful of your setup. Finally pay careful attention of where the electronic scoring loop is on the track. In some cases it might not be marked very well. That will be the place on track that inches can make the difference between winning and losing so be sure to mentally note that one as well.

Now that you walked the track you need to start thinking about how to prepare for practice. If this is your typical race day it is still early in the morning and the air and track temperature is still rising. That means that the track surface will be colder in practice and warmer during the races. In turn the track will have more grip during the race than during practice. So in general you would like the kart to feel a little bit loose at the end of the last practice to avoid experiencing too much understeer during the races. Of course you will have to take into account when your last practice will be relative to when your first race will start. In most cases on race day you will only get two very short timed practice sessions. For that reason you will need some kind of basic strategy so you can efficiently get the most out of practice.

For the first practice the track is likely going to be much cooler and have much less grip so dialing in the handling of the kart will not be very useful. So the goals for this practice are the following:

1. The brakes are working properly

2. The kart tracks straight and doesn’t pull to the left or right

3. The clutch stall speed is correct

4. The engine is working properly and carburetor is tuned correctly

5. Your transponder is working

6. The kart is OK on minimum weight

7. The karts handling is loose

These are simple and straightforward things to check at the first practice but are things that always seem to get overlooked even by veteran racers. I suggest taking it easy the first lap or so and run through the above list on that very first lap. Of course the rest of the pack will be out mixing it up but don’t get caught up in that. There will be plenty of time for racing soon. Right out of the grid is a good time to check your clutch, just mash the gas and note the rpm when the clutch engages. Sometime in the next few seconds check the brakes but do it off line and put your hand up in the air so people behind you know what is going on. You don’t need to get run over by your fellow sleepy competitor. If they don’t, immediately pull off the track and coast to a stop. Get the brakes fixed. If all is OK on the longest straight get up to speed and take your hands off the wheel. The kart should go straight down the track and shouldn’t drift to the left or right. If it does you might need an alignment. Now you need to push things over the next couple laps to make sure the engine feels ok. Don’t forget to listen to the engine especially in the higher rpm areas. If the carb isn’t tuned right this is where it will show up. As the tires heat up take a mental note of the handling characteristics as we will visit that later. When you see the checkered flag slowly pull in and come over the scales. I suggest being at least 3 lbs heavier than the class minimum to be safe. It is far better to be 3lbs over than 0.3lbs under and DQ’d.

Now that first practice is over its time to go over the kart with what you learned. If the clutch stall speed was not correct now is the time to change it. If the kart was pulling one way or the other you need to do an alignment. If the engine was running right you need to check the max rpms and confirm your gearing is correct. If it’s not, fix it now because the next practice is your last shot to get things right. While you are in the pits I suggest you mark the fuel level of your tank with a marker along with the weight when you came over the scales. That way you know you will need to have more fuel than that in it for the races.

With the basics all OK it time to think about setup for this next practice. The track will be better than it was during the first practice but probably not be up to the same grip level you will experience in the race . If you were quite loose the first practice but it was still drivable I would leave it alone as the changing track will help you. If the kart was understeering or tight you need to make a big change to get to the other side of things. If you are tight now things will only get worse from here. The goal for the next practice is by the end of your session the kart should be feeling good and fast. If you can get it there you will be in good shape for the race.

So with that in mind top up your fuel to above the mark you just made, recheck the lug nuts, engine mount, and fuel cap and push up to the grid. As a driver you need to attack this session as if it was qualifying. You need to push the kart as hard as you dare but you need to do it without getting caught up in traffic. Following a slower competitor around for all of practice will not teach you anything about how fast you are. I suggest when you get off the grid you let most of the class go and you work a gap as if you were going to qualify. Use the first lap to warm the tires and do the typical checks. 2 or 3 turns before the finish line you push the kart to the limits. You hit every turn exactly perfectly and mentally note how the kart changes lap after lap. By the last lap you should be happy with the handling or it should be lacking just a little grip. As in the first practice go through the scales and again note the weight at the end of practice. Sometimes the scales used at the tracks are not very reliable and weighing every time you come off will give you a good idea of how close you can get to the minimum weight without getting DQ’d.

OK so now that the final practice is over you have enough info to prepare for the first race. You have the basics covered, the engine is running right, the gearing is right, the handling is very close. You know how much your kart weighs coming off the track and have a idea of how reliable the scales are. With some adjustments that we will cover in next article you will be ready for the first race of the day.

Braking Techniques

Mon, 4 Jun 2012 09:47:05 -0400

Driving a kart is a simple enough thing to do right? I mean you push on the accelerator, turn the steering wheel, and push on the brake pedal ~seems simple enough.

Well if you have been karting for just a day or a 1000 days you know it’s not that simple. One of the areas about driving a kart that seems to get the least attention is braking. I have worked with a number of drivers over the past few years and better braking techniques are something that we can all work on to become more successful racers. It is one of the things that separate the truly great racers from the average racers. This article will help you understand the various braking techniques, some drills to work one and give you some guidance on the physics behind it.

Let’s start off easy and look at the most simple case, braking in a straight line. Imagine you are at top speed (say 50mph) and you simply need to come to a complete stop in the shortest distance possible. You are in a single speed kart, rear brakes only, with a standard hi stall clutch. It would seem like a simple thing to just hit the brakes as hard as you can, lock up the rear tires and slide to a stop. The obvious problem with this approach is that besides flat spotting your tires you will not stop in the shortest distance possible. This is due to the characteristics of friction between the road and your tires. Dynamic Coefficient of Friction (friction generated when sliding) is less than Static Coefficient of Friction (friction generated when there is no sliding between the tire and road). Because of this characteristic the shortest stopping distance will happen when the tires slow as fast as possible without locking up and sliding. Modern day automobiles make this easy on the driver as they all have anti lock brakes. You simply slam on the brakes, the car’s computer modulates the brake line pressure to keep the tires right on the edge of locking up throughout the braking maneuver and the car comes to a stop in the shortest distance possible. Of course karts don’t have such systems so driver skill is the difference between a good stop and a very good stop.

To begin to understand how we need to brake let’s first talk physics and energy. Kinetic energy is the energy of something that is in motion.

The basic equation for kinetic energy is

Kinetic Energy = mv2/2

where m is the mass of the kart, and V is the velocity of the kart.

The act of braking basically turns all of the Kinetic Energy into heat. All of the heat is generated by the brake pads rubbing against the brake rotor. Looking at the equation as the mass goes up the Kinetic energy goes up in a linear fashion. But as the speed goes up the energy goes up by a square of the velocity. Simply put the faster the vehicle is travelling, the amount of energy required to stop it goes up exponentially.

Why is it important to understand all of this equation stuff? Well if you understand the concept of the equation you can understand the most important part of how to stop in the most effective way. The goal is to turn all of the Kinetic Energy into Heat in the shortest time possible without sliding the tires. By knowing that the Kinetic Energy is a function of the square of the velocity you will realize that you will need to apply a larger brake force to the brake pedal at high speeds and decrease the pedal force proportionally as the speed of the kart slows down. Knowing this and applying it is key to maximum braking effectiveness.

One thing that makes braking so difficult in most karts is that you only have rear brakes. The reason why this is such a big deal is because when you start decelerating the weight on the rear of the kart will transfer forward. When this happens the amount of grip capacity of the rear tires drops. In simple terms, besides the fact that you need to compensate for the kinetic energy being related to the square of the velocity, as you brake harder the rear tires get lighter making it easier to lock them up. Anti lock brakes on karts would be a good thing to have huh?

So knowing all of that, let’s get back to the kart. As mentioned before in the simplest case you are travelling in a straight line at 50mph and need to stop as quickly as possible. The most effective braking technique will be to get the tire to the very edge of locking up as quickly as possible. Then as the weight transfers and the speed drops you will need to decrease the amount of force you are applying to the brake pedal to keep the tire right on the edge.

In technical terms the first part of the braking maneuver is called the initial apply. Getting this part done quickly is critical. The reason why it is so critical is because at the beginning of the braking maneuver at 50 mph you are travelling at 73 feet per second. Every 0.1 second you delay getting the tires to the maximum braking point you burn up 1.7 feet. We all know that missing a turn in point by 1.7 feet is a big deal so getting it right is important. The perfect initial apply with be a very quick, hard apply that will bring the tire right to the very edge of locking up as quickly as possible. It seems simple enough but it will take quite a bit of practice to get it right. After you have the initial apply down you will need to reduce the pedal force in proportional to the karts speed in order to get stopped in the shortest distance. Getting it right will require a significant amount of practice and a good consistent braking system on your kart.

I recommend this simple drill to help with the most simply case. For this drill you will need to have a track that has very little traffic on it or a very hard braking zone in it. Basically you just focus on braking in a straight line to a stop or to a very slow speed. If there is anyone at the track with you I highly recommend that you explain to them what you will be doing so they don’t run into you when you do it. It would also be good to choose a place on the track that is off the racing line. Pick a braking point on the track, a crack in the asphalt, a skid mark, or even a cone if available. Come up to speed and when your front tires cross that mark, hit the brakes and show down as fast as possible. Again a quick hard initial apply followed by progressively less pedal force as the kart slows. It will take a number of tries to get it right. When you do you will feel and hear the rear tires chirping, just barely locking up all the way through the stopping maneuver. The other thing you will notice is that you can stop much faster than you ever thought you could. With more practice you will learn to brake like that every time until it is instinctive.

But not so fast, you are not quite ready to set the track record yet. To truly go fast you need to learn the skill of trail braking. Trail braking is simply when you continue your braking maneuver into the turn. This technique is something that veterans already do and beginners struggle with. But one of the big differences between a fast driver and a slow driver is how well you can trail brake.

The reason why trail braking is so important is because it allows you to take your braking points even deeper because you use part of the corner to slow the kart down. The problem of course is that besides the modulation of the brakes that you have to do because of the weight is transferred off the rear tires and the rapid reduction of Kinetic Energy, when you turn the steering wheel you unload the inside rear tire. By turning the wheel your braking contact patch acting on the road is cut in half. You will have to really learn to modulate the brakes as you turn the steering wheel. The more you turn the steering wheel the less braking you can ask the tire to do. If you try to brake too much while turning you will spin. Brake too little and you miss the corner. But lucky for you the same basic techniques you learned while braking in the straight line applies in the case of trail braking. The trick now is you will need to learn to modulate the brake pedal as you turn the steering wheel.

For this drill I usually find a corner on the track that requires quite a bit of braking and is a fairly low speed turn. Approach the corner as you normally would and have a friend mark with a cone or some other kind of marking device exactly where you hit the brakes. Now your job is to brake later than that point and work to carry the brakes all the way to the apex of the corner. Don’t worry about the proper line or making a good exit yet. This exercise is meant to give you more experience braking at the limit and turning at the same time. Once you learn to modulate the brake pedal as the velocity drops, weight transfers, and the steering wheel is turned you will be able to apply new skills to the track. This will become a powerful tool and help you lower your laptimes.

As you work through this exercise you will also come to realize you will be able to use trail braking to help make the kart turn. This is a very powerful skill to develop. Applying a little too much brake while turning will cause the kart to rotate into the corner more. In situations where you are fighting an understeering kart, or racing in the rain, advanced trail braking will be a very valuable asset to have. The catch is, like most things in life, it takes a considerable amount of practice to master this skill.

To practice this skill use the same corner you did in the original trail braking maneuver but this time use the steering less and use the brakes to rotate the kart into the corner. More brake force will rotate the kart into the corner. Less will straighten the kart out. Don’t even think of trying to do this until you master just normal trail braking. This final braking skill is the most difficult and the one that will take the most time to learn to do. But given enough time and hard work you will be able to do it. Just be ready for a few off track excursions on the road to enlightenment.

So there you have it. I suspect after you read this you’ll realize how much you have been taking braking for granted. It is a very important and powerful skill to develop. Use these drills to better your skills and ultimately better your laptimes. It will take some understanding of the physics involved and lots of work but when you figure it out it will be worth it.

USING GPS DATA TO IMPROVE PERFORMANCE

Mon, 4 Jun 2012 09:13:02 -0400

Probably every one of our readers has used some sort of GPS device. After all, we all have to get to the track and no one buys an atlas anymore do they? The newer smart phones have GPS built in, and my wife runs with a GPS module that traces here route, distance, and speed. But a small percentage of karters are joining the Indycar, F1, and other professional racers and using GPS technology to improve our racing and kart setups.

In professional motorsports, GPS is used to create the Sportvision© graphics you see during the broadcasts. The “pointer” used in NASCAR and Indycar to show the car’s position on the track and speed is generated by the same Honeywell GPS system used on the Navy’s Tomahawk missiles. This system is accurate to within 2cm, and Indycar teams can buy the data from the system to overlay the driver’s lines with pinpoint accuracy. But the system is $20,000 and you would have to have Defense Department security clearance to buy it. Fortunately, there are much more affordable GPS systems available for karting!

Earlier this summer, I needed a new toy and bought an AIM GPS05 system. I had tested an earlier version of the AIM GPS system, and have to say I wasn’t real impressed. However, like everything else in the world of electronics that is constantly improving, the GPS05 is a very effective data acquisition tool.

The AIM GPS05 system comes with the GPS module and a two-port data hub that allows you to use the GPS module simultaneously with the E-box. The data hub also has power wires to use an external battery to power the data system. However, should one chose not to use an E-box, the data hub is not necessary. The GPS05 module will plug directly into the MyChron4 dash and run off the dash’s internal nine volt battery (take a spare battery though, the power usage increases greatly).

No matter which way one chooses to hook up the AIM GPS05 system (with or without E-box), it is essential to have the latest GPS firmware installed on the MyChron4 unit. All AIM software is available on their website and is free: download it onto a data key and install onto the MyChron4 (once the data key is installed to the “EXP” slot on the dash, turn the dash on, and it will automatically update).

Once the correct GPS firmware is loaded onto the MyChron4 and the GPS05 unit is hooked up, there should be a “VIEW” setting on the dash that displays the GPS speed and the number of satellites the GPS module sees. Depending the cloud cover, other atmospheric interference, and one’s position the number of satellites will vary. Generally, the more satellites the better the accuracy.

It is also from this screen that the user can set a start/finish line for the GPS system to use for lap timing, thereby negating the need for the infrared beacon receiver on the kart and transmitter placed trackside.

The first step is to enter the MyChron4 dash settings and change the beacon from infrared to GPS. This will activate the functions at the bottom of the GPS view page. Follow the instructions at the bottom of the GPS VIEW screen, after a couple of clicks “OK” the GPS start/finish line for that track is permanently stored on that dash. This can even be done without the kart running, so before practice even starts it’s advisable to roll the kart out to your desired start/finish position and establish it; you do have to remember to change the track name in the MyChron4 dash settings. Once that “beacon” point is set, the MyChron4 will remember that GPS position every time you come back to that track. For those of us who have left a beacon transmitter at every track across the country, this is a Godsend!

Installing the GPS05 system is easy. Using high-strength Velcro and/or ty-wraps, mount the module to the column fairing or somewhere it is safe and has an unobstructed view of the sky. Then, either plug the GPS module directly into the dash or the data hub. If using the data hub and an external battery, you will also have to mount it to the kart and wire the power cord to the battery. The power cord is plenty long to mount the data hub on or near the column fairing and run the power cords to a frame mounted battery like a TAG or Rotax would use.

After installed and hooked up, turn the MyChron4 dash on for a few minutes and allow it to find some satellites. If on the GPS VIEW page where it shows “N. Sat” (number of satellites the system sees) as one or more, the system is ready to start logging!
After an on-track session, the GPS data is downloaded the same way as E-box data via AIM’s USB download key. But the GPS data greatly increases the amount of valuable information one can evaluate in the Race Studio Analysis software – and this is where the performance advantage is!

GPS Data Evaluation
With Race Studio analysis open, the “GPS” icon across the top of the screen will be active if GPS data is present and the system is functioning normally. However, before beginning any data analysis, one must make a functioning track map. Fortunately, the AIM GPS system makes this much easier than it was in the past with speed, beacon, and lateral G sensors.
Assuming the track map is saved and applied to this data set, one of the first items to evaluate is the GPS data by clicking the “GPS” icon that is across the top of the screen. This will bring up an overhead GPS view of the track that is colored in the whole blue to red spectrum. At the left in the measures bar, it will tell the user what channel this spectrum represents (engine, speed, temperature, etc.); click on any of the colors in the measures bar to change the channel and ranges represented by the colors.

With the GPS speed as the selected channel, one can easily see where the kart is accelerating and decelerating and minimum and maximum speeds. By zooming into a specific corner, there are some assumptions the tuner can make about the kart’s handling or driver’s performance. For example, under heavy braking the color will probably change from red to blue in a short distance. In mid-corner, the color should be blue (the slowest point of the corner). If it starts to fade to a lighter blue, implying speed is gaining, and then goes back to the darker blue (slower), either the driver is accelerating too early and the chassis breaks traction requiring the driver to decelerate.

For more detail in a specific corner, run the mouse over any point of the track and it will tell you the specific reading for the selected channel. This can be especially valuable when evaluating the minimum RPMs or speeds for clutch and gear setting.
With the GPS page, one can overlay multiple laps from the session or even different drivers. If the lines cross often, the user can tell a lot about the drivers’ styles; for example, one driver might drive in deeper and “diamond” off the corner versus another driver who goes in easier and “rolls” the corner.

There is also a “front view” as if you are standing at the beacon looking due north and laying level with the track. This view is valuable for evaluating gear ratios and engine tuning on a track that has drastic elevation changes. The three tracks used for data samples in this story, NCMP, Daytona’s infield sprint track and Orlando Kart Center, are nearly flat and this feature seems to have little value.

The GPS data page also allows for overlapping of multiple laps. By overlapping multiple laps, one can explore –with an acceptable amount of accuracy different driving lines and how they effect the cornering speeds.

For example, looking at the screenshot of the right hand hairpin at the end of Orlando Kart Center’s long straight we can see the difference in two laps. Lap one uses an inside line and lap two uses a wider outside line. Running the cursor over each lap trace shows the speed at varying points around the corner; remember, any parameter the GPS and MyChron4 displays can be compared here (RPM, speed, G-forces, etc.). What we learned from this was the outside/higher line all the way around the corner was faster.

A complete session can be exported to Google Earth and overlaid with a satellite image of the track. Google and the AIM exported KML file automatically calculate this. The less laps in a session the better for comparing driving lines; we found that Race Studio even exports “Disabled” laps to the KML file, making it very cluttered. However, there is some value to this overlay: one can evaluate the consistency of their driving.

Each lap is displayed on the Google Earth map by yellow lines, so there is no differentiation to tell which lap is which. The accuracy is very good, especially considering the cost of the AIM GPS05 versus other GPS units; in our sample export, there was only one straightaway/corner that showed us driving off the track out of eight laps.

Generally, the Google Earth overlay can tell the user if there is a lap (or two) that use a significant driving line variation; then the user can go into the Race Studio analysis page and evaluate the GPS data (lap by lap) in greater detail to see if the alternative line is faster or slower. Also, this overlay can be manipulated to show the overlay at an angle (like if you were looking out the windshield of a helicopter). This “birds eye view” of the track can help the driver recall where he/she passed karts, tried different lines, or made mistakes that cost them time.

Another added feature in Race Studio for the evaluation of GPS data is the Track Report. The Track Report uses the GPS color spectrum for a particular channel from one or more laps along with ‘markers’ at key points on the track with that channel’s reading. With two laps selected (from the same session), one can drag the cursor to certain spots on the track and view the RPMs at that spot for both selected laps. This could give the user insights into why/where a particular lap was good or bad and if the gearing is correct.

The Track Report is also very valuable with evaluating the handling of the kart. By looking at the lateral and linear G-Forces, the tuner can interpolate how the chassis is handling compared to other runs. Lateral G’s will show if and where in the corner the kart might be loosing traction and linear G’s will show braking forces and acceleration.

Finally, another of Race Studio’s newest and most helpful functions for driver evaluation is the Lap Replay feature. This feature will work with data from either GPS or the E-box. For showing a driver (young drivers especially) where they are losing time on the track, Lap Replay is one of the most helpful tools in Race Studio because it looks like a video game. Lap Replay allows the user to simulate two laps (from the same or different sessions) on the screen simultaneously; essentially, two dots –one representing each lap, race around the track map.

On the bottom of the screen are “Start/Stop” and forward/reverse buttons. Just above these buttons are “Distance” and “Time Diff” logs comparing laps one and two. These tell the user how far ahead (or behind) in feet and seconds lap one is compared to lap two. Can you believe nineteen feet difference is over .2 second?

On the right of the Lap Replay screen is where the user can select the laps they want to compare and select two data parameters to monitor in real time (most often this will be RPM and Speed). Watching all of this data and the “racing dots” together gives clues as to where one driver is losing time to another and helps answer those proverbial questions: “am I overdriving”, “am I down on horsepower”, and more.

AIM also has GPS Manager software available to make working with the GPS data and system easier. With GPS Manager lap times can be recorded without any previous operation, leaving old systems out: neither infrared or magnetic beacons nor track inspections before tests. GPS Manager allows lap and split beacons to be communicated directly to the MyChron4.

GPS Manager allows the user to create, import, export, and modify tracks. The software uses one of two file types to create the map: the GPK file (for users with GPS data) and the KMB file type (for users of the Smarty Cam).

Creating the track with data from the MyChron4, I was able to take a track map of New Castle Motorsports Park (in the long configuration, used at TAG World Finals in 2010) and preset the GPS end of lap beacon and two GPS splits, therefore, creating three track sectors like Formula 1 uses. Each beacon or split is calculated off the exact (to the millionth) GPS coordinate and many include altitude above sea level –for example, NCMP is approximately 1052’ above sea level (in contrast Homestead-Miami Speedway was 26’ below sea level).

The main benefit we see with this program is it allows the user to pre-program every track they’ve been to (for their next trip) or use a track map from AIM Sports’ ever expanding database of track maps from around the world. If altitude is an issue for jetting, this will also give the engine tuner some insights into what jet to install before leaving for the track.

Conclusion:
In conclusion, the AIM GPS05 is a great addition to the MyChron4 for providing the tuner and driver with more detailed information on their performance. For the budget minded or “newbie” to data analysis, this system trumps the E-box tenfold! There are no sensors for speed or even beacon receiver required, so it makes the kart much “neater” in appearance.

One thing that impressed me was the accuracy of the GPS data versus the earlier models. Honestly, the first version of AIM’s GPS did not impress me –showing half my laps were run through a neighboring cornfield. However, the new GPS05 unit is really good! You can actually use overlays of laps to compare driving lines as advertised.

AIM has added a number of features to Race Studio to take advantage of the data provided by the GPS system. It has made track mapping a one step process, and combined with the color spectrum for individual channels it doesn’t take an engineering degree to evaluate the data.

This article just scratches the surface of how data acquisition and analysis will improve and expand via the GPS platform in the coming years. For the average karter, the first step to taking advantage of the data is to understand the value of analyzing data and overcome the “fear” of downloading!

REBUILDING THE WALBRO FOR THE KT100

Mon, 4 Jun 2012 08:29:09 -0400

In today’s struggling economy, racers are turning to an old friend to allow them to race while keeping costs down. That friend is the Yamaha KT100 2 stroke engine. These engines are simple, easy to work on, easy to get parts for - and while they are not as powerful as the TAGs and Shifters - they are much easier on the pocketbook. With some help from my friend and engine builder Bill Willis of Powersports, this article will explain how to rebuild the Walbro carburetor in order to keep your KT100 running strong while saving yourself some cash in the process.

What does a carburetor do? In simple terms, a carburetor mixes the fuel and air into the right combination so that combustion will take place inside the engine in the most efficient way. The Walbro carburetor does this by pumping fuel using rubber diaphragms, metering holes, and vales. Like anything, these parts occasionally need attention and rebuilt.

Before we get into the details of the rebuilds, I have a couple recommendations regarding carburetors. While you can use a completely stock carburetor off the shelf, it won’t allow your engine to perform at its peak like a blueprinted carburetor. A blueprinted carburetor is a fancy term for a carburetor that has been gone over in extreme detail. These carburetors have all of the manufacturing tolerances taken out, specs matched to the kind of engine you are running and overall brought up to the limit of the rules without being illegal. This is the kind of carburetor you should start with, and is the kind of carburetor that you should learn to maintain yourself. I recommend sending a stock carb to a reputable engine builder and get it blueprinted. In most cases you can get one done for less than $100. Of course you can run a completely stock carburetor but my experience says it will cost you a couple tenths in laptimes.

Rebuilding
Start by removing the airbox from the carb. Since the airbox is technically part of the intake track, it needs attention as well. If you are using a filter inside the airbox, remove it and clean it thoroughly with a good cleaner and allow it to dry. The inside of the airbox will be coated with oil and need cleaning as well. This is best done by using a little bit of brake cleaner and a paper towel. Make sure the inside of the airbox is spotless and perfectly clean. Just remember that when you put it back on the carb whatever foreign particles are not cleaned out will end up in your engine.

Next it’s time to take the carb off the engine. Typically this means using a 4 or 5mm Allen wrench to loosen the 2 bolts holding the filter cup and carburetor to the engine. Gently remove the bolts and remove carb from the intake manifold. Take care not to tear the gaskets between the filter cup and between the carb and the intake manifold. If the carb sticks to the gaskets, gently tap the carb with the end of the screwdriver to pop it off. In most cases you can get the carb off the engine without damaging the gaskets. But in some cases you will tear them and they will simply need to be replaced – no big deal.

Before you start taking things apart, I suggest you clean the outside of the carb thoroughly with carb cleaner or brake cleaner. The last thing you need is for dirt on the outside of your carb getting into the inside during your rebuild. While you are cleaning, inspect the throttle cable attachment for wear and for play in the throttle shaft itself. Too much wear and the pieces will need to be replaced.

Once the carb is clean, it’s time to get into minor surgery. There are 2 kinds of rebuild kits available: the diaphragm only version and the complete kit. We will be going through a complete rebuild in this article so you will need a complete rebuild kit from your local kart shop.

Things You Will Need:
• A very clean place to work
• 2-3 Bins to organize and hold parts
• A small Phillips screwdriver
• A small standard screwdriver
• A small pick
• A pop-off gauge
• Patience

I suggest completely disassembling and inspecting first, then step by step assembly with new parts. Let’s walk through the disassembly first.

Starting with the pumper side (that is the side that has the 90 degree pulse fitting on it), remove the four bolts to uncover the pumper diaphragm. You will find a paper gasket that will likely stick to the cover and a rubber or nylon mesh looking diaphragm. Gently peel the gasket off and scrape any leftover gasket from the cover. Place the gasket and diaphragm in the small bin of old parts.

Now closely looking at the carb side of the pumper, you will notice several orifices for the fuel passages. You will also notice a small screen covering the largest of the holes. This is the final filter to catch particles from the fuel line before it enters the engine. Often you will find this screen full of debris. Your complete carb rebuild kit will include a new screen so with your small pick, carefully pop the screen out and place it in the discard bin.

Now moving to the metering sides of the carb, (the side with the hole in the center) remove the four screws to uncover the metering valve. When you remove this cover be careful not to force the cover off. Older style diaphragms have captive centers that positively attach to the fulcrum arm. If you force it straight off you can bend the arm. To avoid this issue after the cover is loose slide the cover toward the high and low speed needles. Underneath the cover you will find the diaphragm against the cover and another paper gasket. Just like the pumper side peel the diaphragm off the cover and place in the discard pile.

Looking at the metering side, you will see a lever arm attached to a small needle-like valve. This valve opens and closes with the pulses of the engine to provide the proper amount of fuel to the needle circuit. This valve will eventually wear out. To remove the fulcrum arm spring and needle, remove the single Phillips head screw that holds the fulcrum arm axle down. As you remove the screw, put your thumb over the fulcrum arm to avoid the spring making all of the parts fly everywhere. After the screw is removed, gently remove the fulcrum arm, spring and needle for inspection.

The fulcrum arm spring is something you need to reuse and pay attention to. If you have a blueprinted carb, it is likely this spring is special because it is cut to produce a predetermined set pressure or ‘pop off’. The valve inspection is relatively simple. The tampered end of the valve is made of rubber and is graphite coated. The coating will wear away and show the orange rubber underneath. If the bare rubber is visible it is time to replace it. Of course if all is good, place it with the fulcrum arm and spring for re-use.

While working on the meeting side, you will see a half-moon cover with 2 flat blade screws. Remove the screws. With a small screwdriver, gently pry the cover to get it to pop off. Underneath you will find another diaphragm and gasket. Discard these with the others.

For the final disassembly remove the low speed needle (the big T) and the high speed needle and inspect. Look for scratches or grooves around the taper. It is rare to damage one, but if it is damaged, place it in the discard pile and purchase a new one. Also, under the high speed needle you will find an o-ring and a washer. Remove both of these. If the o-ring is worn, replace it. Like the needles, it is somewhat rare to wear one out.

The final step of the disassembly is to thoroughly clean every circuit, and surface of the carb. For this job I recommend an old tooth brush and some brake cleaner. Use the toothbrush to scrub the outside of the carb free of any grease and grime. Spray into each hole and circuit to make sure the entire circuit it perfectly clean. Safety glasses are recommended. I can tell you from experience brake cleaner in the eye hurts! After the carb is thoroughly cleaned I recommend you let it dry completely before re-assembling. Brake cleaner and rubber diaphragms don’t generally get along so well.

Reassembling the Carburetor
Before we start reassembling things, you should be aware that the rebuild kit you purchased is made for more than one version of the carb, so there will be parts and gaskets that you will not use for your carb. I will explain how to identify the ones you want to use and which ones to discard. Also in several steps the order at which the gasket or diaphragm is placed is important, so please take note.

We will reassemble the carb in reverse order starting with the high-speed needle. Put the spring on the needle, then the copper washer, then the o-ring. Screw the needle in until it stops. Don’t tighten too hard as you can damage the needle and the carb itself. Next, screw in the low speed needle until it stops, using the same discretion.

Starting with the metering side, find the 2 half moon paper gaskets and the matching rubber gasket in the rebuild kit. Use the paper gasket with the dumbbell looking slot with holes on each end, and discard the other paper gasket. Place the remaining paper gasket down on the carburetor first then put the rubber gasket on top of the gasket. Then put the steel cover on top and tighten the 2 taper flat blade screws.

Next is the fulcrum arm and metering valve assembly. For this you will use the new valve and the old fulcrum arm and spring. Place the spring down in its hole in the carb and put the new valve into the slot on the short end of the fulcrum arm. Carefully lower the fulcrum arm down into the carb allowing the metering valve to slide into its hole. Slide the fulcrum arm axle into its slot and tighten the small Phillips head screw.

You can adjust the fulcrum arm height on the carburetor. This height is the depth the fulcrum arm below the top surface of the body of the carb. Typical fulcrum height is 0.045 to 0.060 in. This number is dependent on your engine builder’s preferences so you will need to talk to him to get the correct number for your engine. To measure it you can use a simple depth gauge or many kart shops sell a fulcrum height gauge. Adjusting it is a simple matter. Using your thumb gently hold the metering valve in place while pushing down or prying up on the fulcrum arm with a small screwdriver. If the fulcrum arm height is too low, you will need to pry the arm up. If the arm is too high bend it down.

Now it is time to check the pop off. Using a pop off gauge with a small rubber nipple attachment, you can quickly measure and set the pop off. To properly set the pop off you will need to make sure the valve seat is wet. To do this, squirt a small amount of WD40 or similar product into the area around the metering valve. Gently press the fulcrum arm down a couple of times to make sure the oil gets down into the valve seat. Now using a pop off gauge, place the nipple of the gauge into the large hole on the pumper side of the carb that had the screen over it during the disassembly. Slowly pump up the gauge until the carb needle audibly pops. The highest pressure you see before that sound is the carb’s pop off pressure. Like fulcrum arm heights, pop off pressure varies greatly depending on the kind of engine you are running (Super Can, Pipe and so forth) and the engine builder’s preferences. Usually pressures in the 9-12 psi range are normal but to get it right for your particular engine contact your engine builder and use his recommendations. If the pop off is too low you will need to increase the strength of the spring. To do that you need to stretch the spring out. If the pop off is too low you will need to soften the spring. This is typically done by cutting coils of the spring off. Whatever direction you need to go keep in mind that slightly stretching or cutting even half a coil of spring can be a big effect on pop off pressure. As you can image, setting the pop off is an iterative process and can take some time. Don’t rush it and get it done right.
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After the fulcrum arm and pop off pressures are set, it’s time to put things all back together. Looking at the metering side place the paper gasket on the carb body using the small pins cast into the carb body to properly hold the gasket in place. Next find the metering side diaphragm in the kit. This will be the one with an aluminum disk in the center with 5 holes in it. Look closely at the pin in the center of that disk. If you are looking at a simple pin with no notch in it you have the new style, non-captive diaphragm. If the pin has a notch in it you have the old style. I haven’t seen a difference in performance between the two styles but the way you install the two styles is. For the non captive one you simply put the gasket with the aluminum disk face down on top of the gasket. For the captive style you will need to slide the pin into the fulcrum arm slot holding it in place. Like the paper gasket the diaphragm will line up with the locating pins cast into the carb body. With that all lined up correctly, put the metering cover over the rubber diaphragm and tighten down the four small screws.

On the pumper side, you will need to locate the pumper diaphragm and pumper paper gasket. The gasket will be the one that matches the skeletal shape of the inside of the pumper cover. Carb kits usually come with two kinds of pumper diaphragms. One will be black and made of rubber the other will be a brown-ish color and have a mesh look to it. The brown one is intended for use when alcohol is ran though the carb but some builders claim this one will outlast the black rubber one. I haven’t noticed a difference so you can choose as you like or if in doubt ask your engine builder his preference. Either way with the pumper cover on the bench put the paper gasket on the cover using the locating pins as a guide to help orientate the gasket. Next, place the diaphragm on the gasket again using the pins as a guide. Now hold the gasket cover in your hand, and with the diaphragm up, place the carb down on to the cover. The locating pins will let you know that you have it all together correctly. Now put the carb down on the bench with the pumper cover up and screw the 4 medium size screws down snug.

Putting it all back on the engine is an easy matter. Just remember the gaskets between the carb and the manifold and the carb and the filer cup. Like the other gaskets, inspect and replace as needed. Some filter cups use a rubber o-ring in place of a paper gasket. It will need inspection and replacement as needed too. Put your newly cleaned airbox back in place and your carb is now in top form and ready to work at its peak.

So there you have it – A complete carb rebuild that anyone can do. It does take some time and patience but it will save you some money in the end. For the quicker rebuild when you are having issues at the track I suggest only replacing the two diaphragms on the metering side and on the pumper side. I don’t suggest messing with pop off or fulcrum arm height at the track. Most of the time you are experiencing troubles at the track it is because the diaphragms are worn out. Also, setting pop off or fulcrum arm height is not something you can easily do in the pits. Save it for the workbench at home.

PROPER TESTING PROCEDURES:

Mon, 4 Jun 2012 08:10:01 -0400

What to do to truly develop your racing program.

NKN tests a lot of karting products. Most of the time this involves going to the track and getting some laps in – an excellent perk! Years ago when working in Indycar racing, I was one of the few guys who actually enjoyed going to the track for the long and monotonous days of testing –that’s where I learned the most. And out of all this testing, I get one reoccurring question from many karters (phrased many different ways): “How do you test?”

That’s a deep question and has lots of possible angles. However, for many karters the first question that needs to be answered is: do I need to ‘test’ or do I need to ‘lap’?

Here’s the simple difference: testing is learning how changes on the chassis and/or engine setup effect performance. On the chassis side, testing is determining what different geometry changes, different bolt-on parts, and the combination of both affects the performance. For engine testing, it might be different carburetors or carb settings, different exhaust lengths, different fuels and oils, and/or different engine builds (like different port heights via base gasket changes).

Lapping, on the other hand, is just that: pounding laps. It’s the repetitive process of making laps around a track to improve the driver’s line and consistency. Lapping is not pitting every three to five laps and making any chassis change. Ninety percent of karters would be much better off lapping. Ninety-nine percent of karters under the age of twelve should just do lapping days at their track.

For a lapping day, the toolbox should be simple and light. Bring an air pressure gauge, chain lube, and fuel. While that might be bit of an exaggeration, it’s not far off. The setup on the chassis should be the ‘baseline’ setup the factory advises you to begin with, and the engine should be ran a bit on the conservative side (for example, a bit richer and/or lower RPM than race-recommended). The idea is to pound 100+ consistent laps ~not caring about the lap times, just the fact the driver can hit his/her marks every time. This is not testing. This is learning to drive a kart near its limit of control as consistently as possible.
The baseline setup the manufacturer provides with the chassis should be at least 90% as fast and comfortable as anything you come up with while testing”. Also, by lapping with this setup, you will understand the inherent design characteristics of the chassis better. Even though they all look the same, no two karts are driven the same!

So now that we’ve established the difference between testing and lapping, when do you know you’re ready to “test”? There are a number of opinions on this.

When working in “big car” racing, you always thought you were testing. Some drivers, you were merely making changes to shut them up. It’s the same in karting.

Assuming the baseline setup is on the kart and the engine is functioning properly: if the driver is more than three quarters of a second off the pace on your average kart track (8-12 turns), he/she probably needs laps. It takes restraint to not tell dads and karters who are four seconds off the pace and blame the chassis, tires, or engine (when I can see all are good) that it’s not their driving. Sometimes, we all just need more laps to figure it out!

On the other hand, if the driver can shut their eyes and guide their kart around the track with one hand (exaggeration again) and they’re less than .4 seconds off the leaders, maybe a developmental test is what they need for their chassis, engine, or other components!

There are different tests in motorsports. Often, to do any more than one properly in a single day is nearly impossible. First, establish what you are testing: chassis setups, engine tuning, or tires. In the following paragraphs, we’ll outline procedures for testing any and all of the above; however, testing in motorsports is very goal specific and unique to the specific driver, team, and equipment. For that reason, use this as just an overall theory on testing procedures, not a guideline.

Chassis Testing
It is very easy for karters of any experience level to look at a time sheet at a race and panic if they’re not on the leader’s pace. They may listen to six different people at the track (all of whom are on different chassis). And the next step is usually “throwing the kitchen sink at it” –making a large number of guesses on the setup in hopes they’ll make up the lost time. This isn’t proper operating procedure. Don’t panic, a couple of days of testing can help.

Before leaving for the test, there is some homework to do. First, know the baseline setup the chassis manufacturer recommends. We’ve heard the phrase, “that kart is fast out of the box,” that baseline setup is what they’re referring to… Many importers and manufacturers have this setup online or available to email or fax to you. Laminate it –that setup is your starting point and “reset” point if you ever get lost. Second, study the track you’re going to run: know the lap times for your class, know how the track changes, has there been a big event lately to “rubber-in” the track, etc. Also, know that your engine package is solid and consistent; it doesn’t do much good to go chassis testing if you spend the whole day tuning the motor.

The final thing to do before leaving for a test is to make a list of the parts and changes you want to test. There is a logical order to doing this, and that is somewhat based on your kart’s baseline setup. For example, 90% of the time, OTK produced chassis run the “N” axle. So your first changes probably would not be axles. That being said, you don’t want to waste time with fine tuning adjustments and remain half a second off all day.

There are two ways to do a general chassis test. One is to establish a goal for the testing. For example, “today we want to know how the chassis is effected by changing front bars”. Therefore, after a few baseline lap times and feel is established, the first 40 laps of the day’s testing will be trying four different front bars.

When learning a new chassis, one typically uses the method of testing described first –let’s call it the “development testing” (because you’re developing a database of knowledge on the product). The karter’s goal here is to learn what the chassis does when a change is made. How change X effects the turn-in, apex grip, and exit handling, for example.

NKN does a lot of chassis evaluations every year, and when time permits we like to use this method of testing to really learn what the chassis does. Below is the list of things, in order, we do/would do when “development testing” a chassis:

How does seat position effect handling: recommended, forward, backwards, raised?
How does a softer and harder axle effect handling?
Third bearing hooked up or loose?
Second set of seat struts?
Rear ride height: neutral, high, or low?
Front ride height: neutral, high, or low?
Different front bars?
Addition of rear and/or side torsion bars?
Increase/decrease front and rear track width?
Increase/decrease Caster?
Increase/decrease Camber?
Toe in/out 2mm from stock?
+/-3 psi of tire pressure: front/back?
Different wheels: aluminum vs. magnesium?

In theory, each change does the same thing on every kart; a law of physics right? Not always and never to the same exact amount on different brands of karts. Over the years, I’ve switched between many brands of chassis and more than once have had to “relearn” how to tune the new chassis.

The other method of chassis testing is the Pyramid method, where you “build” on the baseline setup. Start with changes to the “big things” (seat position, axle, ride height) and then moving up the pyramid to the small, fine-tuning adjustments that give you the ultimate lap time. This method is typically used when testing at a track in preparation for a specific event. One thing to be cautioned about when using this pyramid method: Know how the track changes throughout the day or weekend.

There isn’t a specific order to the changes, but the idea is to eliminate the big stuff first (while you have the time) and be at a point to make the small changes when the clock is ticking. Another tip to deciding what and/or how much to change using the pyramid method is to assign numbers according to how poorly the kart is performing.

For example, the driver comes in and says the kart is oversteering. The tuner asks, “on a scale of 1-5, five being the worst, how bad is the kart?” Driver replies: “four”. This probably requires a big change: seat position or axle change.
Tuner: “Where does it begin to get loose?”

Driver: “As soon as I turn the wheel, it’s like I’m on ice. The kart has no bite, it’s on top of the track.”
Solution: softer axle and allow the chassis to flex more; therefore, getting the tires to ‘bite’ into the track harder. An axle change is a big step in building the bottom of the pyramid for chassis testing. It’s not a quick change or something you want to change three times in a day.

After the next run, the driver says, “It’s still loose, but a 2-2.5 and only from apex off.” This is a middle step on the pyramid, and might be a softer front bar or a track width adjustment –something that is easily changed back after the next run. For this example, let’s assume a softer front bar is the answer by reducing the amount of rotation in the rear of the kart from the corner apex off.

Finally, the driver says, “It’s nearly perfect. There is a slight bit of oversteer on the exit of the corner.” The tuner has reached the top of the pyramid and raises the rear air pressure by .5 psi! This was an over-simplified example of a pyramid test, but it’s a great illustration how to narrow the problem down via “big changes” first. It may make a Thursday or Friday at the track busier, but less stressful than if you were at the same point on Saturday.

While data acquisition can help in developing or learning a chassis setup, this is still primarily a feel thing for the driver and a visual thing for the tuner. No commercial system on the market designed for karting can accurately tell you if, for example, oversteer was decreased 20% by the last change. Data is there to support and reaffirm what the driver and tuner believe they are respectively feeling and seeing.

Chassis testing takes time, whatever method you chose to use. Chances are, you will not complete every reasonable change in one day. Also, it is important to know that what works (and to what degree it works) in April may not be the same in July when it’s 25º warmer and there is a 1/2” of rubber on the track. To develop the optimum setup or knowledge base on your chassis: Plan on testing in every weather condition possible!

Engine Testing
In this era of high technology and laziness, you’re probably asking, “Why would I need to test an engine? My builder dynos them and tells me what to set it at.” True, but the dyno doesn’t always simulate the real-world track. Have you ever heard, “This engine is as good on the dyno as X’s who’s winning all the nationals,” then later discover it can’t get out of it’s own way? For that reason, we test engines before going on-track race weekend with them.

Engine testing is a lot more “black and white” than chassis testing. Are you going faster thanks to added horsepower and/or a better usage of the power you have? Engine testing is about numbers: RPM, speed, and time, plain and simple!

If the chassis isn’t working and the driver can’t hold onto a consistent line the engine test might be useless. Also, if the chassis is good and the driver is trying to set a track record every lap, the information might be flawed. You should also know if the track is greatly effected by temperature, wind, or other conditions. A track like New Castle Motorsports Park changes up to four seconds between 10am and 3pm in the spring. This can flaw the results too. To properly test an engine the chassis, driver, and track need to be as consistent as possible.

Like chassis testing, there is some pre-track homework one must do to have a successful engine test. If you have multiple parts to test, know each part’s setup and specs. For example, if you’re going to test Yamaha Supercan carburetors and the dyno says: “carb one is the highest peak horsepower, but carb two has the widest power-band from 10,300 to 11,800 RPM” know which is which and where the carburetor’s optimum needle settings are. If exhaust is tunable (for example via different flex lengths), have the different lengths cut before you go to the track.

Occasionally, engine testing is exactly that – Swapping engines that the builder has set up in different ways to figure out which port height, cam (4-cycles), ignition timing, etc. is better. When doing this, it is important to eliminate as many variables as possible. Use the same carburetor, clutch, fuel, and exhaust system if possible. This will give the builder the best results for the internal engine differences.

Evaluating different gears, trying different clutch stall speeds (where applicable), and exhaust systems is also part of engine (driveline) testing. The main thing to consider when evaluating any engine change is to keep as much consistency as possible by only changing one item at a time. Additionally, one change can affect the other. For example, a better carburetor might increase RPM 300 revolutions and require the operator to drop a tooth on the rear sprocket to keep from running out at the end of the straight.

Data acquisition is much more valuable with an engine test. With different parts or engine setup, the speed and RPM curves can easily be seen when overlapped and any differences can be seen. Looking in more detail, the engine builder can zoom in on the top of the RPM graph to see if the line is consistently rising or begins to level off (stop pulling).

Ultimately, a successful engine test will probably come down to the stopwatch (assuming the driver is being as consistent as possible on the racing line). The combination that provides the highest straightaway speed, gets off the corners at the highest RPM, and provides the lowest lap times will trump all others.

Tire Testing
At NKN, we’ve completed a lot tire tests. I’m proud to say we’ve been key test drivers in developing sprint tires for many Burris, Hoosier, and MG and of course we’ve tested Bridgestone, Dunlop, and Vega for numerous articles over the years. Tire testing is a blast for us!

Again, establish your goal(s). Are we looking for speed, consistency, longevity, or repeatability over numerous heat cycles?
To start any tire test, it’s best to have a set (new or used, but of the compound you are testing) to establish a baseline setup. It’s not fair or accurate to test Bridgestone “B” (medium) tires on a setup developed around an MG HZ (hard) tire.

Again, before hitting the track there are some things you need to know. What is the optimum hot pressure for the test tire? What is the ideal operating (hot) temperature? Do I need to balance them before running? What is the roll out (stagger) of the tires?

First, establish a baseline setup that is “neutral” on used tires. It shouldn’t be too easy to drive, but too much sliding will negate the results of the test. Look at the tires for “graining” (or that cheese grater look) on the tires –this will tell you if the tires are over or under inflated and if you have too much positive or negative camber. This is known as “reading a tire”, and is a topic for a whole other article.

Before each test run on the tires, note the cold pressures. And after each run, note the hot pressures, temperatures, circumference, and number of laps completed. These notes will give you the information onto which to build your results.

With a comfortable base setup established, it’s time to bolt on the new tires. Chances are your fastest laps with any new tire are going to come in the first five laps of the first on-track session. It’s known as the “golden lap”; very few tires get it after the first heat cycle. So if you’re going to do an absolute time/speed run this is the time to do it.

After that ‘mock qualifying run’ to gauge the absolute speed of a tire, the rest of the testing is used to evaluate the wear and consistency of that tire over it’s life. Questions to consider are: how many heat cycles till it “fell off” .5 seconds, how many laps or minutes of running did it take for the grip to be gone, and where was the wear seen first (front or rear, center, inside, or outside).

Finally, when evaluating tires, the track must be a major part of the consideration. Is the surface smooth or rough? Is it known as a ‘new tires are best’ track or can used tires compete strongly here? Does this track usually require camber to negotiate quickly?

Remember, what works at Ocala Gran Prix might not work at Daytona or Jacksonville –both less than 100 miles away. More so than chassis or engines, the keys to a successful tire test are notes: learning what the product does, what it likes to perform better, and being able to adjust to it when the conditions change.

Conclusion
Once you’ve established you are ready to “test” and that you don’t just need “lapping days”, it is important to set goals for each time you go to the track to test.
After a karter learns the value of a true “testing” day, he/she will quickly realize how important testing is. The hard work done before the next event will pay dividends at the next race, and you will have a much more relaxed and focused event.
Visit www.nkn.com for copies of our testing, setup, changes, and other valuable sheets that can be printed off and help you the next time you build your notebook for success at the track!

IT’S A MATTER OF BALANCE

Mon, 4 Jun 2012 07:54:44 -0400

Proper Wheel Balance Leads To Better Performance

One of the easiest ways to make your kart more comfortable, more “friendly” to drive, and overall faster is to accurately balance the wheels. It’s something that big-car racers have known for years. And while their wheels are larger and heavier than ours, kart wheels spin faster, because of the small diameter, and so balance is just as important. Whether you run dirt or pavement, 2 cycles or 4-stroke, properly balanced wheels can make your machine faster and a lot more pleasant to drive.

There are a variety of wheel balancers on the market these days, but nearly all of them use a shaft to simulate the spindle. That shaft is mounted between a pair of very low-drag precision bearings. The whole thing is then suspended in some sort of support framework. The idea is pretty simple; the tire and rim, mounted on a front wheel hub, slip onto the shaft and the heavy side of the combination rotates to the bottom. As you add weight to the high side, the light side of the rim, the entire assembly becomes more balanced. The goal is to get the wheel/tire assembly perfectly balanced so that it will sit motionless regardless of what rotational position it is in.

That part of wheel balancing is easy. And you know that doing things right, I mean REALLY right, is never easy. Ideally you should not locate all the weight on a single point on the rim. That’s because there is a difference between “static” balance and “dynamic” balance. Static balance is the condition in which the wheel/tire combination will sit stationary, regardless of rotational orientation, when mounted on a free-turning shaft. This is easy enough to achieve with a simple shaft balancer and is not disturbed by all the added balancing weight being in a single location on the rim. Dynamic balance, however, is the state of equilibrium in which centrifugal forces on a rotating wheel and tire do not produce any oscillating forces on the axis of that rotating mass. Single-point weighting of the wheel/tire combination can, when the wheel rotates, create unequally distributed centrifugal forces that can make you wonder if you forgot to balance the wheels at all! Since all we really care about is how the wheels behave when they are spinning on the track, dynamic balance is the ultimate goal here.

Years ago car tires were static balanced on a bubble balancer. The mechanic just set the wheel and tire horizontally on the balancer and hammered weights onto the rim at the point that put the bubble in the center. Today’s sophisticated tire dealers mount each wheel on a machine that spins it up to 50 or 60 MPH and indicates where on BOTH THE INSIDE AND THE OUTSIDE of the rim the weight needs to be added. Unfortunately, the relatively low mass of kart wheels and tires has made the accuracy of these machines somewhat unreliable for our use. But we can take a lesson from the basic concept. If we want our wheels and tires to be dynamically balanced, we need to divide the weight that we add between the inner and outer rims. A little more work, but easy enough.

Still looking for more? Want to approach perfect dynamic balance? Try taking the weight on the outside rim half and splitting it. Move half of it clockwise around the rim about 20 degrees. Move the other half counterclockwise about 20 degrees. Now do the same with the weight on the inside rim half. Because you have moved the weights away from the “lightest” part of the wheel, you will need to increase the amount of weight at each location a little bit but, once you get it right, you will be as close to dynamic balance as you can get without a spin balancer.

Is it worth it? Can you feel the result of all that time and trouble? Only you can be the judge of that. But if you haven’t made every effort to achieve dynamic balance of your wheels and tires, well, your kart just isn’t as good as it could be. And if you are the kind of racer who can’t stop looking for that little bit extra in performance, if you’re always trying to find ways to make your kart just a little bit better than is was at the last race, why not give dynamic balance a try?

LISTEN TO YOUR TIRES

Mon, 4 Jun 2012 07:46:42 -0400

They Know What They’re Talking About

In all motorsports, there are similarities that are consistent throughout. All vehicles have motors, drivers and steering wheels. Almost all land-based racing have tires. That means that no matter what you are racing, from karts to Indy cars, knowing how to properly use your tires is the single most important factor in learning to race successfully.

While any number of factors play into how your kart performs, it is the manner in which the tire contacts the racing surface that ultimately decides how fast a racer can go around the track.

There are a few easy ways to diagnose basic tire problems.

“The big word in tires is consistency.” Says NKN test driver and WKA Gold Cup Grand National Champion, Billy Dickson. “In setting up a kart, the best thing to have is all four tires working together to keep the kart on the track.” Also, keeping the amount of work each tire does spread across its entire contact surface is important as well. Toe, caster, camber, ackerman, stagger, crossweight, transfer weight, torsion bars, center of gravity and many other factors all affect how tires perform.”

Tires perform best when they are run within their specific temperature range. If a tire is too cold, it can slide across the racing surface, or it can pick up rubber from the track, causing them to be laden with rubber. Tires that are too hot will most likely begin to blister or feather, again resulting in less grip. This is where the compound begins to break down and air pockets begin to form on the tires surface. They may be minimal, or quite dramatic, depending on the racing situation.

A tire, if run perfectly, should have an even amount of smooth wear across its surface with no blistering or buildup.

“Before diagnosing your problem, it is important to know that remedying one problem with a chassis adjustment like a caster or camber change will likely have an effect on how your kart handles through the corners. It is a delicate balancing act between maintaining your tires and getting around the track fast. “Getting it right is what racing is all about,” said Dickson.

“It is also very important to scale your kart properly before trying to do any effective testing at the track. Without knowing that you have the seat placement and cross weights correct it will be difficult to diagnose any problems.”

Another hint is to be sure and occasionally calibrate your tire gauge to be certain that it is accurate. An inconsistent unit can cause many problems before a racer even hits the track.

“Your tires will tell you where the problems are,” said Combs. “At our track, many karts will develop a push through the turns. The telltale sign is that the front tires will start to feather, usually on the inside of the tire. This means the front tires are sliding rather than gripping.

To correct for a push, you need to plant the front end more and give the tires more grip. We widened the front tires. For more extreme pushing, we added a front end bar - if the kart has torsion bars. Doing so may require you to narrow the tires back down. As you get closer to the proper setup, the feathering should lighten.

If the back of the kart becomes loose, then the rear tires start to look rippled, almost like they are being shredded. This is the opposite of a push. The sign of being too loose in the rear is if the kart starts to hop in the middle of the corner. Narrowing the front tires or removing a front bar should help the problem. Lowering the front frame height may also help to free the front end up.

If the back of the kart is sliding at the entrance of the corner, the rear needs more bite. To stiffen the rear you can resort to longer hubs, a stiffer axle or stiffening the seat struts to give the back more bite. Adding caster to the front kingpin will also increase grip for the whole kart,” advises Combs.

“If our chassis is binding up or chirping in the corners we know that our tires are running too hot. Usually we will see blistering that will confirm this. This is caused by the chassis getting twisted in the corner and then it wants to rebound or unwind too quickly. According to Dickson, “To cool the tires on an American chassis, we will start by widening the wheels out so that the kart doesn’t transfer as much weight going into the turn. I know some European karts will make just the opposite change. Taking caster out of the front end will help as well. This reduces the amount of arch that the spindle travels, thus the kart twists less. If everything on the setup is working well, we will sometimes switch wheels and put the tire on a wider wheel to stretch it out. We might take a 6” tire and put it on a 7 1/2 “wheel. This makes the sidewalls less flexible, again this reduces how much the tires flex, thus the tires will run cooler and more free in the corners.”

If a tire is blistering on the inside it may be due to the kart having too much toe in on the setup. (see toe definition in terms section). While toe may improve how the kart handles in the corners, it may be counter acting the direction of the kart, causing the inside surface to be most affected. Another problem may be the camber. Because camber affects the surface of the tire that contacts the pavement, having too much negative camber will also cause the tires to wear on the inside.
If the tires are wearing on the outside, the opposites may be true for the camber and toe.

If the tires are wearing on the outside and the inside, but the middle is clean, you may be running too low of air pressure. Adding air pressure increases the circumference of the tire. Again, the converse may be true. If your tires are wearing only in the middle, the sides may not be getting enough of the work. Remember consistency is key.

If your tires are picking up a significant amount of rubber on the track, your tires are likely running too cold. “If you came in on a cool down lap and you see rubber building up there is a problem. If you come into the pits and your tires are under 100 degrees then your tires won’t perform the correct way. A good range is between 110 to 130 degrees all the way across the tire. So you need to increase the heat in the tires. Increasing the air pressure should help. This decreases the amount of tire that is contacting the track. The center should heat and disperse across the surface of the tire. Going to a narrower rim or a softer compound will increase the flex in the tires, and more heat will build in the corners. Adding caster increases the lift on the inside rear tire and the amount of twist the chassis gets in the corners. This increases the load on the tires and operating temperatures.”

There have long been debates on compressed air verses nitrogen. According to our resident racer Dickson, the choice is simple. “We carry both. Air carries excess moisture as do the tanks. Keeping the air dry under all conditions is a lot more difficult than just having another tank of nitrogen. If we need to increase the temperature in the tires, we run air (knowing that to some degree they will increase in temperature throughout the race). If we want to run cooler or more consistently, we will run nitrogen.”

Combs adds, “We will use nitrogen when we know that the tires are running hot, but the tires aren’t giving us an indication of why.”

According to Dickson, some racers have turned high tech in managing their tire pressures. ”I’ve heard of some racers using bleeder valve stems on their tires. A racer can pre-set the valves at 12 pounds and throughout the race as pressure builds in the tire the valve releases the excess. I don’t even know if they are legal, they are on the inside of the tire so they can’t be seen. They cost about $200.00 a set, which is just another expense to consider.”

When learning to maintain your tires, there is still no substitute for simple practice. “What kills me is the number of racers who put their kart away Sunday night and get it out the next Sunday morning and expect they are going to win races. In our program we do extensive testing and record keeping so that we know what to do in certain situations. We also maintain our karts. We lubricate and clean the bearings, tune the clutch and minor things throughout the week to make sure we are ready to race. Many times local racers think that the guys on the national level only know how to cheat to win. When we kill them at the local races they want to look at tech and find out where we have cheated instead of looking at our program and understanding how much we put into it week after week. We come to win, whether it is a national or a local track. We have records clear back to when we first started. Every track, and event is there for us to reference. Everyone on the national level does this. That’s the key to winning in racing,” said Dickson.

RACING INTELLIGENCE

Mon, 12 Mar 2012 08:26:30 -0400

New Technologies Remove The Guess Work
By Bob Chiras

Generally speaking, karting does not maintain the statistics relative to qualifying and race lap times. If it did we would all be impressed with the parity that is occurring within the sport. Complete fields are being set with one half second separating the field.

In years past this type of parity was only found at the very top of the racing world.

So what has changed? The answer is surprising; the advancements are attributed to karters’ learning to turn race data to race intelligence through the advent of data acquisition and data analysis systems available today.

Since karting began, successful racers have depended upon data collection and have learned how data elements relate to one another to achieve performance and reliability. Because there were no early tools, the sport became overloaded with many myths and supposed secrets were circulated among racers. Great amounts of misinformation have been circulated from karter to karter. Worse than circulation of misinformation, the myths were often a contributing factor to racers leaving or criticizing the sport.

Realizing the need to turn race data to race intelligence companies took a creative approach and developed instruments and software addressing the need of competitors.

Race Data Begins With Data Collection.
For years racers performed data collection. There were notebooks that filled a drawer in every racers toolbox, some thought they could perform data collection with their memory and some took it a bit further and had a statistician associated with the race team.

In the early days, all we had was a simple Tach to give us our RPM’s, and a temperature gauge to tell us what the cyclinder head temp was. One was good for choosing gear ratios, the other was good for setting up the carbuerator. Today we have instruments that certainly do both of those, but show us how we are actually driving the course…graphically. Unfortunealty, there are still a large number of teams that use those expensive devisces as nothing more than a Tach and Temp gauge.
Data collection is essentially recording, organizing and storing data that can be retrieved for later analysis.
These are a few of the factors that are considered in each tuning decision.

The reason that we differentiate between race data and race intelligence is that almost anyone can collect race data. The ability to turn the data into race intelligence has been dependent upon years of experience and a lot of the race budget spent on bad decisions.

From a practical sense take a look at how this plays out each weekend at the professional level. NASCAR allows limited use of data acquisition and data logging. Crew chiefs use race data and the analysis of the team engineer and the collective experience to deliver performance intelligence. The starting fields all qualify with speed of less than 1/2 second apart. Why is it that at the conclusion of the race some teams are many laps behind. It is not the lack of data it is the lack of turning the data into race intelligence. Bad setup, bad strategy and poor tuning of the chassis or engine are the causes for poor performance and are the result of poor race intelligence.

There are a host of decisions that have to be considered when applying race data. Two significant decision points to consider are driver comfort and driver preference.

Most of the decisions that impact the outcome of a race are made prior to the vehicle reaching the starting grid. A talented driver needs performance and handling to apply his driving skills. Even the best driver can only carry an ill prepared vehicle just so far.

How do you gain race intelligence rapidly, reliably and inexpensively? There really are no schools or apprenticeship programs and even if there were most fathers would not have time to go spend hours, days, weeks or months in training programs to learn how to develop race intelligence. Families want to race as often as possible, to participate at as many race venues as the budget allows and to perform to the best possible level with the sons and daughters being on the podium at the conclusion of the events.

The answer is that today we have instruments and we have vendors that provided software that turns race data into race intelligence.

Software allows visualization of each lap of practice or a race. The average racer can visually review the relationship between RPM’s, exhaust gas temperature, cylinder head or water temperature, miles per hour, lap times and even when the clutch engages.

Rather than racers having to learn how each of the factors are related, software engineers have selected key elements and have chosen to graph race data to race intelligence. For comparison purposes the capability to overlay laps is provided for the racer to perform analysis. Ten different inputs are simultaneously converted from race data to race intelligence. I’ll venture out of my realm here and assume that one of my professors was correct and will repeat his hypothesis that most humans can only process seven different inputs at one time. Through the advanced software the racer is getting almost twice the number of inputs processed and presented in a form that is easy to comprehend by a basic racer.

I regularly conduct seminars for racers and teach the use of race intelligence. We begin with the basics of how to use the data as race intelligence, then we review some of the norms such as what is a reasonable RPM range for the motor being run, what are reasonable temperature ranges, exhaust gas and cylinder head or water for the motors being run. What fuels are being used as gasoline and alcohol each requires a different air/fuel ratio.

Once we get past the basics we then move on to what are the causes of the curves, bumps and squiggles of the graphs being analyzed. We cover what the chassis, motor and the driver cause. In advanced sessions we examine the impact of tires and tire pressure. As the racers assimilate more we then move on to the effects of jetting and timing and how changes in each are reviewed in the data that is collected by their on board data acquisition systems.

At an event I attended a father of a novice driver told me that that the kart was bogging down on the back shoot because of the instrumentation on the kart. I downloaded the data from his instrument and then proceeded to remove each lead from the instrument. I coiled the tach lead, the CHT lead, the MPH lead and the EGT lead and wiretied them under the seat of the kart. I put a transponder on the kart so that I could get lap times from an independent source and after another practice round we examined the facts. The lap times were worse after disconnecting the leads. The issue was that the driver was exhausted; he had been out for every round of practice and had just lost the desire to the drive that day. The father had lost sight of the fact that sons or daughters are not professional drivers and that parents need to look at the data and learn to talk with them about why the driver is not performing at peak performance.
Racers do not always give the best feedback when they are tired.
Using data acquisition we can see the characteristics of the racer getting tired. Racers begin their corner entry too soon, they pick up the throttle too late on exit and the driver begins to get more dependent upon the brake and less dependent upon the inherent characteristics of the chassis to get the correct grip in the corner. The bad exit speed will always result in bad speed on the straights.

If you are not using race intelligence to your advantage you are missing one of the real opportunities to go fast consistently with the minimum of expense. You can achieve what it has taken many top tuners decades to learn in a few months.
The best news of all is that the software application for converting race data to race intelligence is “free” on the Internet.

ANALYZING SPARK PLUGS

Fri, 3 Dec 2010 10:57:41 -0500

Learning to read sparkplugs is one of the best ways to understand exactly what is happening inside your engine. Whether it is “Carburetion Day” at Indy or “Happy Hour” in Winston Cup, anyone who has spent time in the pits of a professional motorsports event will attest to the numbers of crew chiefs and tuners who are looking through plug scopes at their spark plugs trying to determine what carburetion and ignition changes need to be made.

The first step in understanding spark plugs is learning how to read the number code on the side of the plug. Each manufacturer has a different formula for their numbers, which you can usually get, from the dealer where you buy the plugs. It is best to rely on these charts as we have found automotive cross-reference charts to be inaccurate, especially in the plug heat range.

The numbers tell the diameter of the spark plug, the reach of the plug –(how far it goes into the motor), the heat range of the spark plug, if it is a resistor or non resistor type and sometimes the definition of the electrode is included. Some manufacturers have as many as eight digits on a spark plug to identify the characteristics of a spark plug.

The first thing to look at is the size of the spark plug. Most sparkplugs’ thread diameter is 14 millimeters. There are some other sizes (10MM. 12MM and 18MM), but they are rarely found in any karting application. Because differences in thread diameters are so large very few people get into trouble through trying to apply a l4mm plug into a 12mm hole or vice versa.

Plug Length:
The reach or the length of threads often trip racers up. There are four normal reach lengths; 9.5MM or 3/8-inch, 11.2MM or 7/16-inch, 12.7MM or 1/2-inch and 19MM or 3/4-inch. Having either too short or too long of plugs usually results in some type of engine malfunction.

There are two potential problems that can arise if plugs are too short. First, by shortening the length, a tuner has effectively enlarged the head area and lowered the compression. Secondly, a short plug leaves the lower threads of the cylinder head exposed to heat and contamination making it difficult later on to install a plug with the proper length.

If the plugs are too long, then the threads extend into the combustion chamber and are no longer protected by the walls of the head. The exposed threads then absorb heat from the combustion process. This raises the plug temperatures and may take them up high enough to make the side electrode glow white-hot. If this happens it will begin firing the mixture far too early causing pre-ignition or detonation. Overheated plugs also have the potential to come apart and destroy pistons and valves, ruining the engine. A single exposed thread in an engine’s combustion chamber will raise electrode temperatures. Most karters who are following the recommendations of their engine builder do not get into these situations, but we often find novices who are relying upon some local experts having spark plug length issues.

Resistor or Non-resistor
There are also resistor and non-resistor spark plugs. At the moment the spark jumps the gap it causes a high frequency burst of energy, this is known as RFI (radio frequency interference). Placing a resistor within the spark plug suppresses the RFI. Without resistor plugs in your car you can experience static on your radio as well as interfere with other sensitive electronic equipment. Some later model vehicles as well as newer Powersport engines must use resistor plugs for a proper “talkback” to the electronic ignition. Outboard marine Capacitive Discharge Ignition (CDI) such as used on some Johnson and Evinrude marine engines require a special inductive type resistor. Use of non-inductive resistor type plugs on these motors can cause misfire and poor performance.

For most karting applications, it is necessary to use a resistor type plug. The resistor plug uses a 5K ohm ceramic resistor to suppress ignition noise generated during sparking. Without the resistor plug it is very likely that a racer will experience interference with any electric instrumentation on the kart, especially any of the newer data acquisition systems.

Heat Range:
Before you venture into heat range one lesson is a must. Spark plugs are not thermostats. You do not change plugs to make a motor run hotter or cooler.
Spark plugs have to stay hot enough to burn away deposits (oil, carbon, etc.) that otherwise would short-circuit the plug. In most four cycle engines we see plug temperatures from a low of 500+ degrees to a high of 1000+. degrees. In two cycle motors we see the temperatures slightly higher with lows being in the 700+ degree range and high temperatures in excess of 1200+ degrees. Some of the spark plugs using the more exotic metals such as Iridium Platinum or Premium Platinum can run with temperatures in excess of 1500 degrees. This will all depend upon the fuel air mixture and the compression ratio that is selected by the engine builder.

Heat range is determined by altering the length of the path the heat travels from the center electrode and insulator nose cone to the plug shell and the plugs threads. A plug with a long insulator nose, which leads heat into the plug body before it reaches the cooler cylinder head, are “hot” plugs, and those with a shorter heat path, are “cold.” plugs. The terms “hot:” and “cold” for plugs can be very misleading, the engine puts heat into the plug, the plug does not increase or decrease engine temperatures. A “hot” plug does not make an engine run hotter nor does a “cold” plug make it run cooler.

Nearly all of the spark plug manufacturers use a number-based code to designate heat range: Europe and Japan follow a system in which higher numbers mean colder plugs; American companies do just the opposite, assigning hotter plugs higher numbers. Racers should always review the manufacturers specifications prior to installing any plugs.

For spark plug terminology click here
Briggs 4 cycle engines have large intake ports angled toward the head and the spark plug. The Briggs plug is positioned in the path of the intake flow and the alcohol fuel and the large volume of air tend to cool the spark plug tip. Many engine builders use hot plugs to overcome this issue and to keep the plug from fouling. Racers use surface-fire plugs in the Briggs motors especially in SuperStock, Limited and Modified classes where the stock carburetor is replaced with a carburetor and a high volume fuel pump. We have run these motors where we could deplete a one-gallon fuel tank in fifteen laps on a 1/4 mile oval track. Surface-fire plugs don’t have a specific heat range. They run at about the same temperature as the combustion chamber’s walls are immune to overheating and run very well in these high performance motors.

Do not let the price be the determining factor in the plug that you select. We have tested plugs that cost in excess of $10 each and have selected NGK or ND plugs which are available for a few dollars each and often found better dyno results with the less expensive spark plugs. The expensive plugs where developed to solve problems like those caused by superchargers or altitude extremes that really do not apply to karting.

Reading the Plug:
Once a racer or tuner has an understanding of the dimensions of a plug and how they effect the engines performance, they can move on to reading the various surfaces of the plug to understand how it is performing in the engine. The best way to look at a plug is to use a plug scope. A plug scope is a device that is basically a magnifying glass with a flashlight attached used to closely inspect the surfaces of the spark plug.

The first rule to understand is; do not try to read old spark plugs. Even the experts find it difficult or impossible to get accurate results from doing so. It is best to start with a clean slate and new plugs are the only way to gain information about what is currently happening inside the engine. New plugs can give you a complete picture after just a few minutes of hard running or a couple of really good laps.

It is important to get a clear picture of what is happening when the kart is under race conditions. Therefore it is important for the driver to kill the motor while they are still on the track. We usually ask the driver to pull the spark plug boot off of the plug so that the motor stops and we do not idle the motor down pit road. When the kart comes to a complete stop, we remove and inspect the electrode’s tip with a plug scope.

First the edges of the electrode should be examined for any rounding that has occurred from melting. Rounding is an indication that the spark plug is overheating. This can be caused from either incorrect fuel air mixture or incorrect ignition timing.

The tip of the ground electrode may also show signs of eroding, another sign of overheating.

Analyzing Plugs To Improve Performance
Next, inspect the condition of the insulator, which should be white. A porous, grainy appearance is evidence of overheating. If the signs of overheating are confined mostly to the center electrode, then the engine has too much ignition timing.

If an engine has its timing only slightly advanced, then a fuel buildup will be visible along part of the center electrode and end close to the tip. The reason for no build up at the tip is that the tip is sufficiently hot to burn off any fuel buildup. If you are sure that the engine timing is correct, the issue may be that the heat range of the spark plug is several ranges too cold. It takes careful analysis to determine the cure, so always get your engine builder involved before making wholesale timing or plug changes.

When you look at a freshly removed plug from a two-stroke engine and make decisions based on the color of the oil deposited on the insulator nose you are likely passing a meaningless or incorrect decision. We see plugs that are just wet and know that the mixture is far too rich but the real analysis takes place by reading the insulator deep inside the plug body. The insulator is coolest where it contacts the metal shell, which is where you “read” your mixture setting. Look far inside the plug, where the insulator joins the shell. If the engine’s mixture is too rich a colored ring will be present. If this ring continues outward along the insulator to a width of even a millimeter you can be sure the mixture is rich enough to be safe, and too rich for maximum performance.

In most engines best performance is achieved when the mixture contains only enough excess fuel to make just a wisp of a “mixture ring” on the plug insulator.
Karting 2 Stroke air-cooled motors like a slightly richer mixture, which provides internal cooling and lubrication. Briggs four-stroke engines give their best power when the mixture is leaned to a point that the last trace of color deep inside the plug completely disappears.

An air/fuel mixture that yields maximum power is only slightly richer than the one that causes detonation. The plug will indicate when there has been even slight detonation inside an engine. The signs to look for are pepper-like black specks on the insulator nose, and tiny balls of aluminum concentrated mostly around the center electrode’s tip.

Severe detonation will blast a lot of aluminum off the top of the piston and give the plug a gray coating. If you find examples of detonation, get your engine builder involved and determine if the motor can be run again or if it needs a rebuild.

The trick in all this is to know enough about spark plugs to be able to choose the right basic type, and to understand what the plug has to say about conditions inside a motor. Reading plugs takes a fair amount of experience and the only way to gain the experience is to become diligent about reading the plugs after each outing. When you have doubts, seek advice from your motor builder or one of the top tuners at the track. You will find that the guys are ready to offer more advice when they find a person who is really making an effort to learn. You will soon learn how to get a lot more performance from your motors by mastering the techniques necessary for you to read spark plugs and understand what they are saying.

SPARK PLUG TERMINOLOGY

Fri, 3 Dec 2010 10:54:54 -0500

Fouling:
Fouling is when the spark plugs firing tip becomes coated with excessive fuel, oil, or combustion deposits so that it is unable to produce a spark. A plug can become fouled from continuous low speed driving, improper spark plug heat range (too cold), improper timing (over-retarded), too rich an air/fuel ratio or an oil leak into combustion chamber. A variety of self-cleaning features are designed into most plugs to reduce fouling.

Bridging:
Bridging is when deposits accumulate between the center electrode and the outer shell or base of the ground electrode. These deposits can form a “bridge” for an improper spark path from the center electrode to the outer shell, this will result in misfiring. Depending on application, there are a variety of self cleaning designs used by Champion to reduce bridging.

Pre-ignition:
Ignition of the air/fuel mixture prior to its timed ignition by a spark from the spark plug is referred to as “pre-ignition”. This can be caused by a hot spot in the combustion chamber, improper timing, too hot a spark plug, low octane fuel, too lean an air/fuel mixture, or engine overeating.
For more about spark plugs click here

Flashover:
Flashover is when the voltage sent to the spark plug does not fire between the center and ground electrodes within the combustion chamber. Instead, it shorts between the metal shell and the terminal nut on the plug exterior causing the engine to misfire. This can occur when the air is highly ionized (such as on a stormy day), or when the insulator is dirty. Champion plug insulators are corrugated to reduce flashover.

Quenching:
To understand quenching and how it is reduced it is first necessary to review the basic purpose of the spark plug – to ignite the air fuel mixture in the combustion chamber. To do this your vehicle ignition system generates tens of thousands of volts to jump the gap between the center and ground electrodes. However it is good to know that it is not the actual electricity that ignites the air fuel mixture, it is the heat energy generated by that electricity or spark. Therefore when you are creating the spark you want as much of the heat from that spark to be used to ignite the air fuel mixture and not have the heat from that spark be re-absorbed by the center and ground electrodes. Thus Champion manufactures a variety of designs (cut back ground electrodes, fine wire center and ground electrodes, tapered center and ground electrodes, etc.) all to try to reduce quenching by reducing.

SETTING VALVE LASH

Fri, 3 Dec 2010 10:53:02 -0500

Though there are critics on both sides of the fence when it comes to the benefits of the new Animal engine, one thing that neither side can dispute is how much easier setting the valve lash is on the Animal. Anyone who has tried setting the valves on the Raptor will probably tell you that it is not their favorite feature of the engine. Not only is it time consuming, but it also requires special grinders to do the job. Plus, the Raptor requires the head and valve springs to be removed when a lash adjustment is required.

The Animal engine and most other Over Head Valve (OHV) engines only require a couple simple hand tools and a few minutes to successfully adjust the valve lash. Removal of the rocker cover and sparkplug are all that is needed to do the adjustment.

When you adjust the valve lash what you are doing is setting the mechanical clearance of the related valve train components. This clearance is either specified by the engine or cam manufacturer and is dictated by the design of the valve train. Because metal parts grow with heat from the running engine, their clearance is needed to prevent the valve from being forced open and allowing air to escape on the compression stroke. Other factors that go into the lash specification are related to the manufacturer’s tolerances and the cam design itself. The reason for pointing this out is not because it really affects the average engine builder or racer, but more to show that a lot went into deriving this critical measurement. So keeping it at its specific setting will help maximize your race engines performance. There are two main factors that cause the lash setting to change; the first occurs if the engine or related components were taken apart, and the second comes from wear of the related components. If the engine is taken apart or has had the head, rocker arms, or side cover removed in the tech barn, a valve lash check and possible adjustment are warranted. The main wear component of the valve train is the valve face and the seat. The valve opens and closes at a rate greater than 35 times a second at racing speeds. This constant pounding of the valve against the seat causes the valve to recess into the head. This is not a lot, but when the valve lash is only 3 thousandths of an inch to start with, it doesn’t take much.

Below is a break down of setting the lash on the Animal race engine. Remember to always consult your engine builder before adjusting the lash. They are familiar with what setting will give you optimum power which may or may not be the same as specified by the cam manufacture. Lash can be used as a small tuning agent of your engine’s power band; which your builder might have tweaked for your situation.

Remove the 4 valve cover bolts and remove the valve cover from the engine. In most cases the exhaust system can stay on the engine for setting the lash. The most complicated part of setting the lash is getting the cam in the right position to do so. The lash has to be set with the cam on the base-circle and not the lobes. In other words the cam has to be in the position when it is not lifting the valves. If the lash is adjusted in a position when the valve is being lifted the setting will not be right.

The easiest way to find when the valves are closed is to feel for the compression stroke. This is done by removing the spark plug and putting your thumb completely over the hole and sealing it off. By turning the engine over slowly by hand in a clockwise rotation (when looking at the flywheel), you can feel the engine start to make compression and feel air leak past your finger. Stop turning the engine at this point.

Remember that this is a 4 cycle engine, which means that it only makes compression on every other stroke. This means the piston will also reach top dead center (TDC) on the overlap phase of the cam, but if the lash is set at this point the setting will be dramatically off.

The engine is coming up on the compression stroke so you now must locate the piston at the top of its stroke or top dead center (TDC). The safest way to do this is to reference the keyway in the crankshaft output shaft (PTO shaft). The keyway in the Animal, and most engines for that matter, are in line with the crank throw. This means that when the keyway is in line with the cylinder the piston is close enough to TDC to do your check. This can also be done by sticking a pencil in the spark plug hole and slowly turning the engine over until the engine reaches its highest position.

It is better to set the lash a little past TDC than before. Some cams have mechanical compression releases to make it possible to pull start the engine by hand. What this does is slightly lift the valve on the compression stroke to relieve some of the pressure so it can be turned over easily. This release then swings out of the way when the engine reaches operating speed. The lash can’t be set on this compression release or the setting will be dramatically wrong. By setting the lash a little past TDC you eliminate the possibility of running into this.

Now the lash can be measured with a feeler gauge inserted between the valve tip and rocker arm. Try different sizes until you find the gauge that slides in with little friction but is neither tight nor loose. A good judgement of what is the right amount of friction is the gauge should have just a little friction if held by two fingers, and not just slide out. Likewise, if the gauge falls right out it is too loose. Once a feel for this is established, it will become second nature as to what is acceptable.

If an adjustment is needed then a 5/8” wrench and 1/8” Allen wrench come into play. The rocker adjuster ball is locked in place by the 1/4” set screw on top of the rocker. By holding the adjuster with your 5/8” wrench you can loosen the set screw with the 1/8” Allen wrench. Now the adjuster can be turned either clockwise to tighten the lash or counter-clockwise to loosen it. By inserting the feeler gauge of the right size between the valve and the rocker arm you can adjust the lash to achieve the correct feel of the feeler gauge. Once this is achieved the adjuster can be held in place by the 5/8” wrench while the set screw is tightened back down.

How often you should check your valve lash is probably best left up to your engine builder. My recommendation would be every 2 hours of run time would warrant checking the lash. In my experience if everything is working and built correctly, and the engine is past its break in period, seldom will it require adjustment.

Compared to the days of the past when specialty tools were needed to adjust lash the new OHV engines make the adjustment an easy addition to your pre-race prep. I wouldn’t recommend doing this for the first time at the track because if you would have problems it could ruin your race day. Practice in the shop not just once, but a couple times until you are proficient at the process. Then have your work checked by an engine builder to make sure it is done correctly. When you feel comfortable with doing the adjustment, having the ability to do it quickly at the track could be a savior some day.

Tip: Though this procedure is an example of setting the lash on the Animal engine, most other OHV engines are much the same. This procedure can also be used to help with other manufacturers OHV lash adjustment.
Mechanics Tip- Briggs has installed a thread locker patch onto the adjuster ball set screw to help with reliability. This patch works so well that at times loosening the _” set screw with the little 1/8” Allen wrench can be difficult. When this is the case heat may be needed to loosen the patch. Do not heat the adjuster ball on the engine, use your 5/8” wrench to remove the ball with the set screw from the engine. Once the pieces are away from all flammable materials the adjuster ball can be heated up in a vice and have the set screw removed.

PVL IGNITION COIL

Fri, 3 Dec 2010 10:50:47 -0500

The newly released ignition system from Briggs and Stratton is an innovative step for 4 cycle racing engines. It replaces the transistor type coil that was designed over 25 years ago with new digital technology. The new PVL digital system provides the racer with a product that is lighter, more robust, and more accurate than the systems of the past. The digital technology available today made it possible to develop this affordable system for our racing application. Unlike most digital systems, it only requires the integrated magnet in the flywheel to power the system.

The new PVL system can be utilized on all 3 of Briggs and Stratton’s kart racing engines; the Animal, World Formula, and Raptor can all be easily retrofitted. Starting in 07 both the Animal and World Formula will be available out of the box with this new technology. The system should prove to be comparable to the old system yet still posses some qualities that will make it a justified change over for the competitive racer.

PVL, located in Germany, specializes in the production of digital ignition systems for many performance applications. They started producing ignitions in 1970 and have since formed a reputation for producing high quality products around the world. PVL manufactures ignition components for such companies as BMW, Buell Motorcycles, Mercury Marine, Polaris, Vortex and numerous others. Their top notch ISO 9001 certified manufacturing facility proves to be the perfect match for producing the new Briggs and Stratton racing coil. They have the experience, technology, and quality that is required to make a reliable system for today’s 4 cycle kart engines.

Related Articles
Setting Valve Lash
The new PVL coil is physically bigger in size. This is because it must have enough spread of the coil legs to pick up energy from the flywheel magnet and power up the system before the plug is fired. This allows it to “think” and have the ability to adjust the spark timing independent of the magnet position to the coil. The coil’s bigger physical size is of no negative affect to the engine. The coil is designed to mount in the same location as the original coil on all 3 of the race engines. Christy Matuszewski, the Motorsports engineer at Briggs and Stratton assures us that extensive thermal surveys were done to verify that the coil has no adverse affects on engine temperatures. The concern was the bigger coil could affect the air paths from the cooling fan to the cylinder. Testing proved that the new coil had no effect, neither positive nor negative, relative to the standard coil. The flywheel is constructed of a die cast aluminum main body with an integral steel center hub. The steel center hub makes for a more rigid design capable of maintaining a consistent taper when removed and replaced multiple times. This rigidity helps combat loss of timing due to a slipped flywheel. The integrated steel hub also has provisions to be used with a professional style flywheel puller. This center pulling flywheel puller is a more efficient way to remove the flywheel for the engine builders. Check out the tool of the month section on page 38 for highlights of its operation.

The flywheel incorporates a rare earth magnet that is cast into the outer edge and pinned into position. This magnet produces the energy to power the whole system, including powering up the control module and firing the spark plug.

The coil’s operation is more complex than the original transistor coil because of its digital characteristics. The theory of general operation is much the same. The flywheel magnet passes by the lamination stacks, as the opposing poles pass the legs of the coil energy is transferred up the lamination stacks to produce the energy needed to power the electronics and produce the spark. The original coil had a north-south-north pole orientation as the flywheel passed by the coil legs. The new PVL system has the pole orientated in a south-north configuration which is required for the proper operation of the coil. Unfortunately, this means that the new coil will not operate with flywheels from past designs. But, rest assured, companies like ARC Racing already have drawings in the works for aftermarket flywheels that will utilize this new pole orientation for modified applications where a different flywheel may be preferred.

The following is a breakdown of the coil’s operation as the flywheel magnet passes by the coil legs. The magnet passes by the coil from left to right with the leftmost leg seeing the magnet first. The left leg uses the energy it gets from the magnet to charge the capacitor (electronic storage device) for future use for firing the plug and to power up the processor. The processor’s job is to tell the plug when to fire in reference to the crank position and relative to what has been programmed into it. The system is two-dimensional; this means that it adjusts the timing relative to the engine speed only. In other words the timing can be varied up or down depending on the current speed of the engine.

The processor’s main job is to monitor the engine’s speed and tell the capacitor when to discharge, or send power to the coils to produce spark. By calculating the speed of the engine and the correct amount of time needed to produce the desired spark, the system can precisely position the timing of the ignition. The first leg of the coil produces the power to get all of this started.

The second leg is the trigger reference for the processor. This trigger location is used to calculate the spark advance and pick up the engine speed as the flywheel magnet passes by it. By calculating how much time it takes for the engine to make one revolution it can calculate the average engine speed and make adjustments to the timing as required.

The third leg’s function is to help aid in spark energy output. The CDI (capacitive discharge ignition) uses the energy stored in a capacitor to send current to the primary coil which is ultimately stepped up in the secondary coil to produce the high voltage needed for spark. This third leg gives the system the positive feature of having a secondary current source which helps amplify the capacitor’s voltage at the time of spark and ultimately increase the spark’s duration. When the timing is set within a certain range, as it is in our particular case, the spark duration is amplified because of this extra energy. In fact, so much that its spark duration is actually longer than its transistor counterpart in certain areas of the speed curves. This increased energy associated with the third leg’s position is only affected by what is programmed into the processor and is independent of the flywheel’s position at the crank. PVL has optimized this for us so the system not only offers the greater voltage potential associated with the CDI type ignition, but also has the longer spark duration normally only seen by transistor type coils.

The fourth leg (furthest to the right) is also a trigger leg. This trigger leg is used in place of the second leg that works with the processor at engine speeds lower than 1000rpm. This is considered the hardware trigger and is there to provide spark before the microprocessor has enough energy to operate. Only during start up is this hardware trigger utilized. At engine speeds greater than 1000rpm the processor takes over and uses the second leg to get its trigger information. The hardware timing is set at 10deg with the standard keyway position to allow for easy starting. Then it has 19 additional degrees of advance even before the engine gets to its idle speed, thus equaling 29degs of total advance. This timing layout helps maximize the spark energy by positioning the third leg in the right location for maximum voltage output as discussed previously.

The coil’s processor also has a rev limiter that can be programmed into it. This was one of the primary assets of the new system for the World Formula racing engine. In the past the World Formula engine had an external rev limiter box that just had a wire going to the standard coil. This system was easy to disconnect leading to a possible tech issue. The World Formula’s rev limiter is now built into the processor so disconnecting it is impossible. The rev limiter is set to the same speed as the original, 7100rpm, and has a max variation of +/-1% of limiter speed. But, testing to date has shown it to be within +/-10rpm. The World Formula and Animal coils are similar in physical design. To distinguish between the two the World Formula coil is surrounded by a red casing and the Animal by a blue one.

Because the coil is digital and programmable, there is some concern that hackers might be able to reprogram it. This would allow them to fine tune it for their application or possibly increase the rev limiter speed. I have been reassured that this is not possible due to the make up of the processor. There are many types of processors and some are reprogrammable, and others, like this one, can only be programmed one time. There is no way to reprogram it more than once and if a change of the program is needed a new one must be utilized. PVL programs the processor at the factory, thus it has been already programmed once and can’t be programmed again. Even if it could, PVL has developed its own programming language which would be next to impossible to copy to actually change the coil’s outputs. Even if it could be reprogrammed the hackers would have to get through the potting material. The entire system is potted inside the plastic housing including many of the fine wires and components that are surrounded by this epoxy-like coating. Accessing the electronics without disrupting all the circuits would be a feat within itself.

Another concern that some have is the fact that many digital systems are very sensitive to overload and can burn down easily. One way it can see an over load is if the spark plug wire is removed. Rest assured that this system is protected against such conditions. Contrary to some myths, the system will not fail if the spark plug wire is removed while the engine is running. Nor will it fail if the engine is turned over with the spark plug wire not hooked up. The system has proven to be very robust, and Christy Matuszewski of Briggs claims that through 1000’s of hours of development testing never have they failed one coil.

How does the PVL output compare to the original ignition? The properties of the CDI give it greater power potential because the primary coil has more energy to work with. The capacitor can store as much as 200volts that is instantly discharged when the processor tells it to fire. The original coil only has the energy provided by the passing magnet which is much lower. Because the two coils basically work like a step-up transformer finding the secondary output voltage is a matter of multiplying the primary coil voltage by the winding ratio of the primary and secondary coil. This means the multiplication of the primary voltage is much higher with the new CDI because of the high voltage stored in the capacitor. The system ultimately gives a higher voltage potential at the plug because this higher primary voltage is then multiplied by the coil ratio.

But remember, the plug will only use the voltage that is required to jump the gap. This voltage requirement will increase as the pressure inside the cylinder increases or the plug gap is increased. So the increased voltage potential of the PVL comes into play if the plug gap is increased and/or more compression is added. Opening up the plug gap could show possible performance gains by initiating a stronger initial burn; a possible but not yet proven advantage of the CDI system for our application. Stronger potential voltage can also help fire through a wet and fouled plug.

The weight of the flywheel for the new system is also lighter and possesses less inertia. This means that it requires less power to accelerate it, allowing for more power to be utilized at the wheels. The difference may be negotiable, but the fact is that it is lighter, especially when compared to the original cast iron version of the World Formula’s flywheel. This lighter weight will only prove to help, not hurt, the engine’s performance.

The change over to the new system is going to require some growing pains. Hopefully, with the help of NKN and all the work that Briggs and Stratton has put into this new system, these pains will prove to be far and few between. Briggs has positioned the flywheel’s keyway where it will work well for most of our racing needs; if an adjustment is required the write up in this issue should help in fine tuning your engine. Change is never easy, but when it is a change for the better it should make good sense to the racer that change isn’t always bad. The unfortunate added expense has many added benefits for our racing engines. After the initial transition, I think most will agree that this new technology in 4-cycle racing is in the best interest for all of us. Racing requires stability, but it should also possess technologies that help progress the generations of Motorsports; otherwise, our car counterparts would still be racing with Model T’s.

REAR END ADJUSTMENT

Fri, 3 Dec 2010 10:48:21 -0500

The rear end of a kart is not only where the power is put down for acceleration, but it is also where the majority of the weight of a kart is, the most moving parts, and one of the more overlooked areas on the chassis. In this article I will try to explain why you need to get your rear end working to get the best performance from your kart.

The first thing we need to talk about is how the rear end of the kart works. Most karts are setup with 55-57% rear weight bias that means the rear is doing more than half of the work to keep you and the kart on the track. The front of the kart has the primary duty to set the direction of the kart and lift the inside rear wheel so the turn can take place. After that is accomplished, the rear end does the rest. Weight transfer, how easily that inside rear lifts, acceleration, braking, and chassis stiffness are all primarily a function of how well the rear end works with the front. When you approach a corner you turn the steering wheel into the corner causing the front of the kart to turn in and through the caster built into the front end it lifts the inside rear wheel causing it to slip. After that point the stiffness of the rear end determines how much grip is transferred to the outside rear tires and how fast it is transferred. Getting that all correct has to do with the stiffness of the rear end components and the track width.

So how do you control stiffness of the rear end? Well there is a number of ways and I will break them down part by part from biggest to smallest effect. Keep in mind I am only talking about the rear end of the kart. That means, axles, bearings, hubs, torsion bars, seat struts, seats (yes, the stiffness of the seat will affect the handling of the kart), how the axle is clamped, rear bumper, and track width. You see while the rear of the kart looks simple enough there is a lot of stuff to work with.

The biggest change you can make to the rear of a kart that will affect the handling is the stiffness of the axle. For those of you who have been to a big race with factory teams you know what I mean. All of the chassis manufactures have several different stiffness of axles available for any number of track conditions. The stiffness of the axle is usually controlled by wall thickness. The thicker the wall of the axle the stiffer the axle, the thinner the more flexible the axle. The rear axle stiffness is one of the most basic and important things to need to get right before you start making any other changes. (Here’s a link to an article on axles, and here’s another one) When conditions are cold or the track is slippery use a stiffer axle. This will help transfer the weight to that outside tire the quickest and most direct way helping to push that tire into the track. For conditions when the track is hot and sticky you need a softer axle. The softer axle will flex more and will more slowly and less efficiently transfer that weight. That will make the tire able to slide a little more on the hot sticky track.

Next up is rear hubs. Hubs come in a huge variety of sizes and shapes and they work very much like the axle does. They manage the weight transfer to the tire contact patch through the stiffness of the axle. The hubs work like a stiffener for the axle. A long hub will overlap more axle therefore making the whole axle system stiffer. A shorter hub has the opposite effect. It clamps around less of the axle allowing more flex. Use short axles for sticky high grip situations when you are experiencing understeer. Use long hubs on cold slippery days when your kart is too loose.

Ok now, let’s talk rear track. When I talked about the effect of hubs and axles I was only talking about using those parts without changing the rear track width. (Here’s a great article on adjusting track width) That is if you are running with a 55in rear track with short hubs and the kart is loose you put long hubs on and keep the track at 55in to get more grip in the rear. But of course changing the rear track by itself can also have a big effect. Widening the rear track does 2 things. First it increases the lever arm to the outside rear tire decreasing the amount of weight transferred to it and therefore decreasing grip. It also will uncover more of the rear axle and allow the axle to flex more also reducing the rate of weight transfer. So changing the rear track can be one of the easiest and quickest ways to tune the rear of your kart. For slippery days when you are loose, narrow the rear track. For days when you have understeer and it is hot and sticky, widen the rear track.

Rear torsion bars are next. Most karts today have adjustable and removable rear torsion bars. These are usually a flattened piece of tubing that is clamped between the rear frame rails. The bar adds stiffness to the rear frame of the kart increasing the rate of weight transfer and increasing the efficiency of that weight transfer. Add the rear bar when the kart is loose and when the track is slippery. When the kart is tight (understeer) and the track is sticky remove the rear bar. Many torsion bars are also flattened to allow you to rotate the flat part to get a different amount of stiffness. With the torsion bar parallel to the ground it is most soft (lower grip) with it rotated 90 degrees to the ground it is stiffer (more grip).

From here the tuning parts become much less effective as the axle, hubs, rear track and torsion bars tend to be the biggest influence on tuning the rear of the kart. But that doesn’t mean that the remaining things should be ignored as in combination they can be a big influence.

The inner race on the rear axle bearings are kind of like rear hubs. They clamp around the axle stiffening the axle in that local area. If you flip that bearing inward so the inner race is between the frame rails you will decrease the rear stiffness of the kart and therefore decrease rear grip. If the inner bearing race in outboard the opposite happens more stiffness and more grip.

Rear seat struts. More seat struts, more rear grip generally speaking. I say that because it also depends on the angle the strut is mounted to the seat and where on the rear bearing it is attached. Most karts that I have driven tend to work best with at least 1 seat strut on each side of the seat. Because the seat struts work with the stiffness of the seat that is in your kart, consult your chassis manufacturer about seat struts and location. It can be different for different karts.

Seats can be a big effect to the rear of the kart but since they tend to be expensive and not so easy to replace it is often overlooked as an effect on the rear end. A seat bolted between the frame rails, triangulated with seat struts definitely becomes part of the chassis system. A very stiff seat will increase the stiffness of the chassis where a softer one will decrease the stiffness. That being said seat stiffness is a fairly sensitive thing to most chassis. Because seats are acting on such a large portion of the kart I recommend changing seats only as a last resort when absolutely nothing else seems to work. Contact your chassis manufacturer for advice but generally speaking stiffer seats will give you more grip and a softer one will be less grip.

The lower bumper bar can also have some influence on your kart. Though you can’t remove it because of the rules you can usually tighten or loosen the bolts holding it in place to change the stiffness. A loose fitting bumper bar will decrease the stiffness and give you less grip and one that is clamped down tightly will give you more grip.

OK, those are the basics to the rear end and that is a lot of information to work with. Now let me explain how I would go about tuning a kart with all of the tools above. Let’s assume that it is a hot sticky summer day and there is a lot of rubber on the track, the kart is tight (understeer) and can’t seem to break free of the track. Given the number of adjustments you have at your disposal this is how I would attack the problem.

1. Remove the rear torsion bar if installed. This is by far the easiest change to make at the track. If this doesn’t work go to step 2.
2. Widen the rear track in 1cm increments until the problem improves or until you reach the maximum width allowed by the rules or the maximum you can go per your axle length... If that doesn’t fix the problem go to step 3.
3. Change to shorter rear hubs and keep the rear track width what it is from step 2. Again in step 2 if you ended up at 52 in. in the rear, put shorter hubs on and set the rear track at 52 in. If that doesn’t work move to step 4.
4. Loosen the rear horizontal bumper bar if it is not already. Don’t remove it and make sure you use nylon lock nuts so you can run it loose without it falling off as it is needed for the rules. If it is already loose go to step 5.
5. Remove a rear seat strut on each side of the seat. Be careful with this one though. While it does decrease rear stiffness it also will allow the seat to flex more which might feel strange to the driver that is sitting in the seat. If the driver is not comfortable with the feedback he is getting, put it back and move on to step 6.
6. If all of that has been done and you are still struggling with freeing up the kart now is the time to switch to a softer axle and start over again. Changing the rear axle can be a pain but you do want to win right? Make the change and start from the top of the list again.

That is my recommendation on how to go about tuning your rear end on a hot sticky day. On a day when you are searching for grip I would recommend the same order of events just instead of short hubs go with long ones, instead of removing the torsion bar add it and so on. Finally if all else fails consult your chassis manufacturer as they will know best how your particular chassis should work the best and how to help make it work. Make sure you tell them what kind of seat you have in the kart as that will have an influence.

Related Articles
Axle Installation & Removal
Too Much Grip
Front End Adjustment
So now you know how the rear end works, and why it works. You now know there is a lot more back there to work with than at first glance. You also have a basic order on how to attack the problem. So what are you waiting for? It’s the karting season! Get out there and get your rear end working for you!

FRONT END ADJUSTMENT

Fri, 3 Dec 2010 10:46:30 -0500

By now you already know that the front of your kart points you where you want to go, right? You also know that the front of your kart can be quite complicated with all of the adjustments possible right? I mean think about it, caster, camber, Ackerman, toe, track width, steering rate, ride height, static camber, camber gain, torsion bars, can all be used to help get to where you want to go, but that list can be a bit overwhelming to sort out. This article is intended to give you a better understanding on how to go about sorting out the front of your kart.

With that in mind, we need to have an understanding of the terms used to explain the behavior of the front of the kart. Understeer or push is when you turn the steering wheel but the kart does not want to turn. This understeer can be as severe as it causes you to completely miss the apex or as mild as it simply causes you to turn the steering wheel a little more than you like. Oversteer or loose is when you turn the steering wheel and the rear of the kart rotates too much causing you to get to the apex too soon. Generally severe oversteer is best fixed by dealing with the rear and severe understeer is best fixed by tuning the front end. Mild cases of understeer or oversteer can be attacked with either the front or the rear end adjustments depending on what the problem is.

Let’s talk about what each of the adjustments are and why they are important. After we get the definitions out of the way I will share with you a step by step way to navigate through all of them. Let’s start with an easy one, ride height. Front ride height is simply the height of the front-most frame rail right behind the front bumper to the ground. Adjusting the ride height in most karts is a simple matter of moving spacers to the top or bottom of the spindles. Lowering the spindles in the frame yoke, putting more spacers on the top of the spindle, will raise the ride height and raising the spindles, putting more spacers on the bottom of the spindle will lower the ride height. Raising the front ride height will give the front end more grip and lowering the front ride height will reduce front grip. Ride height tends to be a fine tuning type of adjustment in most karts.

Track width is another easy one to explain. Front track width is simply the distance the front wheels are from one another measured from the outside of each tire. Adjusting front track is a simple matter of moving spindle spacers from the inside of the wheel to the outside of the wheel. Front track is one of the adjustments that you can get carried away with and can cause some confusion. (Here’s a great article on track width) Increasing front track will make the front of the kart respond quicker at turn in but will reduce the amount of front grip at mid corner. Decreasing front track will make the kart less responsive on turn in but have more grip at mid corner.

Front track works very closely and is influenced by caster. Caster is defined as the angle of the front kingpin as viewed from the side relative to the ground. Most karts have caster angles in the 10 to 15 degree range. Adjusting caster varies from kart to kart but in most cases involves using eccentric pills that change the angle of the kingpin. Tilting the kingpin rearward increases caster and tilting it forward decreases caster. Increasing caster will increase front grip throughout the corner while decreasing caster will decrease grip throughout the corner. Caster also has a large influence on the rear of the kart so care should be taken to not only pay attention to the front end while you are adjusting caster but also keep an eye on the rear end too.

Ackerman is one of those terms that people throw around a lot but many people simply do not understand what it is. Ackerman in simple terms is the difference in the left wheel angle and the right wheel angle for a given steering wheel input. Zero Ackerman means that when you turn the steering wheel the right and left wheels turn exactly the same amount as the right. Negative Ackerman is when the outside wheel turns more than the inside wheel for a given steering angle. Positive Ackerman is when the inside wheel turns more than the outside wheel for a given steering input. Most all modern day karts have positive Ackerman built into the front spindle and steering shaft geometry. Ackerman is adjusted two different ways in the kart. The first way is by providing two places on the front spindle to attach the tie rod to. Attaching the tie rod end to the inboard most hole will increase Ackerman. Attaching the tie rod end to the outer most hole will decrease Ackerman. The other way to adjust Ackerman is to change where the tie rod end is attached to the steering shaft. Attaching the innermost tie rod ends as close as possible or even in the same hole will decrease Ackerman where attaching them to outermost holes will increase Ackerman. Increasing Ackerman (making the inside wheel turn more than the outside) will make the front of the kart turn in quicker. Decreasing the Ackerman will make the front of the kart turn in a little slower. Ackerman will also have a very small effect at mid corner but in general only is used to deal with turn in problems. Ackerman may not be adjustable on your chassis. If it is not, don’t worry there are many other ways to tune up the front end.

Camber is the angle of the tires relative to the road when viewed from the front. Negative camber is when the top of the tires are tilted inboard and positive camber is when the top of the tires are tilted outward. Camber is usually adjusted in the same way that caster is. Tilting the kingpin outward will add positive camber and tilting in inboard will add negative camber. Changing the kingpin angle is usually done by rotating eccentric pills in the yoke of the kart. Tilting the tires inboard will remove front grip and tilting them outboard will add grip. I usually set camber based on the front tire wear pattern. If the inside of the tire is wearing quicker than the outside, tilt the tire outboard. If the outside is wearing quicker then add more camber.

Click for more on front track width
In newer karts you can change the steering rate and effort. This is done by changing where on the steering shaft the inner tie rods attach to the steering shaft. Moving the tie rod ends closer to the steering shaft slows the steering down and makes the steering effort less. Moving the tie rods farther away from the steering shaft will make the steering quicker and make the steering efforts go up. Setting the steering rate and effort is largely a driver preference. For young kids a slower steering rate not only makes the kart easier for them to steer but it also smoothes out some of the erratic inputs young kids make.

Just like in the rear the front of many karts have removable torsion bars that change the stiffness of the front of the frame. These torsion bars come in all shapes and sizes from tubes that are flattened in the center to tubes with various wall thicknesses. Making the front end more stiff tends to make the front more responsive and making the front less stiff will make the front less responsive.

OK, now that you understand all of the adjustments that are at your disposal lets talk about how to apply them. Let’s assume it is a hot sticky day and there is a lot of rubber on the track. Your kart is understeering and it feels like it is stuck to the track. This is how I would attack the problem given the tools described above.

Increase the front track. This will increase the weight jacking effect at turn in and will help break that inside rear tire from the sticky track. Be watchful that you do not develop mid corner understeer as you increase track.

Add front bar if not already in. This will make the front end stiffer between the left and right kingpins and allow the weight to be transferred more efficiently. Some karts when you add the front bar in sticky conditions will experience a chassis oop. If it does hop, remove the bar and move to the next tool.

Increase front caster. Tilt the kingpins rearward. This will increase the weight jacking effect lifting that inside rear wheel helping to reduce understeer. Increasing the caster will make the steering more heavy. If it becomes too heavy move the innermost tie rods to holes closer to the steering shaft.

Add positive camber, tilt the kingpins outward. This will get more of the tire surface in contact with the track and help add grip to the front end. Be watchful that this change doesn’t make the front end too twitchy. Some chassis do not respond well to a lot of camber.

For a cold day where you are looking for grip you can go through the same list but simply do the opposite.

Other things to consider when it comes to tuning the front end. If you are having problems with the front being too twitchy consider reducing Ackerman or slowing down the steering rate. If it isn’t turning in quick enough, increase Ackerman and steering rate.

Finally in the end it is important to attack a front end problem by making changes on the front. Sacrificing grip at the rear for an ill tuned front end will not get you to the podium. If the front is not working, tune it up.

WHEEL BALANCE

Fri, 3 Dec 2010 10:43:43 -0500

One of the easiest ways to make your kart more comfortable, more “friendly” to drive, and overall faster is to accurately balance the wheels. It’s something that big-car racers have known for years. And while their wheels are larger and heavier than ours, kart wheels spin faster, because of the small diameter, and so balance is just as important. Whether you run dirt or pavement, 2 cycles or 4-stroke, properly balanced wheels can make your machine faster and a lot more pleasant to drive.

There are a variety of wheel balancers on the market these days, but nearly all of them use a shaft to simulate the spindle. That shaft is mounted between a pair of very low-drag precision bearings. The whole thing is then suspended in some sort of support framework. The idea is pretty simple; the tire and rim, mounted on a front wheel hub, slip onto the shaft and the heavy side of the combination rotates to the bottom. As you add weight to the high side, the light side of the rim, the entire assembly becomes more balanced. The goal is to get the wheel/tire assembly perfectly balanced so that it will sit motionless regardless of what rotational position it is in.

That part of wheel balancing is easy. And you know that doing things right, I mean REALLY right, is never easy. Ideally you should not locate all the weight on a single point on the rim. That’s because there is a difference between “static” balance and “dynamic” balance. Static balance is the condition in which the wheel/tire combination will sit stationary, regardless of rotational orientation, when mounted on a free-turning shaft. This is easy enough to achieve with a simple shaft balancer and is not disturbed by all the added balancing weight being in a single location on the rim. Dynamic balance, however, is the state of equilibrium in which centrifugal forces on a rotating wheel and tire do not produce any oscillating forces on the axis of that rotating mass. Single-point weighting of the wheel/tire combination can, when the wheel rotates, create unequally distributed centrifugal forces that can make you wonder if you forgot to balance the wheels at all! Since all we really care about is how the wheels behave when they are spinning on the track, dynamic balance is the ultimate goal here.

Years ago car tires were static balanced on a bubble balancer. The mechanic just set the wheel and tire horizontally on the balancer and hammered weights onto the rim at the point that put the bubble in the center. Today’s sophisticated tire dealers mount each wheel on a machine that spins it up to 50 or 60 MPH and indicates where on BOTH THE INSIDE AND THE OUTSIDE of the rim the weight needs to be added. Unfortunately, the relatively low mass of kart wheels and tires has made the accuracy of these machines somewhat unreliable for our use. But we can take a lesson from the basic concept. If we want our wheels and tires to be dynamically balanced, we need to divide the weight that we add between the inner and outer rims. A little more work, but easy enough.

Still looking for more? Want to approach perfect dynamic balance? Try taking the weight on the outside rim half and splitting it. Move half of it clockwise around the rim about 20 degrees. Move the other half counterclockwise about 20 degrees. Now do the same with the weight on the inside rim half. Because you have moved the weights away from the “lightest” part of the wheel, you will need to increase the amount of weight at each location a little bit but, once you get it right, you will be as close to dynamic balance as you can get without a spin balancer.

Is it worth it? Can you feel the result of all that time and trouble? Only you can be the judge of that. But if you haven’t made every effort to achieve dynamic balance of your wheels and tires, well, your kart just isn’t as good as it could be. And if you are the kind of racer who can’t stop looking for that little bit extra in performance, if you’re always trying to find ways to make your kart just a little bit better than is was at the last race, why not give dynamic balance a try?

SCALE & ALIGN YOUR KART

Fri, 3 Dec 2010 10:41:31 -0500

So you have your kart ready for the track right? You’ve rebuilt the engine, replaced all of the fuel lines and cleaned it all up. All systems go for a successful racing season right? Well you did align and scale your kart right? No? ARE YOU OUT OF YOUR MIND! Going to the track without aligning and scaling your kart and expecting to do well is kind of like putting cheap gas in a high performance race car. Technically it will work, but it won’t give you the results you want.

I use very simple and straightforward tools to align a kart. Of course if you want to use a $1000 laser alignment system, feel free. I use a set of alignment disks. Alignment disks are available from most any kart shop for around $75. Those, along with a 6ft tape measure with at least 1/16 inch graduations, a bungee cord or a set of vise grips and you have all the tools you need.

Put your kart up on a stand so you can work with it. Take the wheels and sidepods off and put the alignment disks on the front wheels. Take a lThis YouTube Video Might Help!ong bungee cord and hook it on either side of the steering wheel and loop it around the seat. Then adjust the bungee cord until the steering wheel is centered the way you want it to be when the kart is going straight. This is called setting the spoke angle. If your kart has a plastic upper steering support you can set the steering straight ahead and then use a set of vise grips to pinch the support around the steering shaft keeping it from moving during the alignment process. Some people don’t like this idea because it can mark up the plastic.

The first step of the squaring process is to measure the distance from the centerline of the front spindle to the rear axle on both the right and left side of the kart. This is the key measurement to get your chassis square. Most karts have a small detent in the center of the spindle making it very easy to eyeball the measurement. If your chassis doesn’t have the center of the spindle marked, simply use the front or rear of the spindle axle itself. Carefully measure both sides of the kart. If the two measurements do not equal each other you will need to adjust the tie rods accordingly until they do equal. Just loosen the tie rod jam nuts on both ends of the tie rod and turn the tie rod accordingly on the side you need to change. Continue to adjust the left and right side until both are exactly equal. Don’t worry about the toe at this point, just make sure the distance between the spindle and the rear axle is equal left to right. Keep the tie rod lock nuts loose for now since we will need to do more adjusting when we set the toe.

The toe is simply how the front wheels are angled inward or outward relative to exactly straight ahead. To measure the toe simply measure the distance from the front of the right alignment disk to the front of the left alignment disk. If these measurements are equal, the toe is set to zero and your chassis is properly aligned. Toe in is when the distance between the front of the left and right alignment disks is smaller than the rear edges of the right and left disks. Toe out is the opposite. For most karts a good starting point is zero toe or slightly (1/16 in) out. In order to change the toe and keep your chassis squared you will need to go back to the distance between the rear axle and the spindle measurement to change your toe. If the chassis is toed in, you will need to shorten that distance by turning the tie rods in (make them shorter). If it is toed out, you will need to lengthen that axle to spindle distance by turning the tie rods out (make them longer).

Always change the toe by using the axle to spindle measurement as the main basis for change. Make sure you always keep that distance equal when changing the toe. Also it is important to repeat these steps when you change caster, camber or front ride height. Those changes can change the alignment of the chassis. In the end you can do a good, accurate alignment job inexpensively and simply. Oh, and before you finish the alignment, use a permanent marker and put a mark on the steering shaft and upper steering support to indicate where straight ahead is. It will be useful later. Be sure to tighten down the jam nuts on the tie rods and put the wheels and side pods back on.

Ok, now your chassis is aligned and ready to be scaled. You should get the recommended weight percentages from your chassis dealer as a starting point. If you can’t get that info I suggest 43% front weight on the front tires and no more than 1lb difference between the front wheels and no more than 2lb difference between the rear wheels. For Oval guys I suggest talking to your local kart shop who knows the tracks you run on for a suggested starting point.

It is very important to use a good set of scales designed for scaling cars or karts for this procedure. I know we have all heard that four $19 bathroom scales will work, but to be honest they simply won’t. Bathroom scales are spring scales and by design get thinner when weight is applied. Because karts have no suspension that deflection will give you false readings on the corners of your kart. Go borrow a set of scales from a friend.

To get your project started you will need to find a fairly level piece of concrete or asphalt to set you scales up. I am lucky enough have a friend who not only has a nice set of scales, but also a nice leveling stand. This makes setting things up so much easier.

You will need a large, 3ft long or more, carpenter’s level to set the scales so they are all in the same plane. After you have all 4 pads set in place and approximately where they need to be to match the karts wheelbase and track, you need to check the level front to back and side to side. This is a simple matter of setting the level directly on the pads and adjusting the height of each pad until they are all level left to right, front to rear and even diagonally if your level is long enough. This step takes some time but is very important to get right.

After the scales are leveled turned on and zero. I recommend you step on each one as a final check to make sure they all read the same. It would be worthless to scale your kart to a set of broken scales. After that you will need a friend to help you from now.

You will need a clipboard and if your set of scales doesn’t calculate front percentage automatically you will need a calculator. Your kart will need to be exactly like you would expect it to come off of the track at the end of a race. Sidepods, engine, tires and so on need to be ready to race. I also recommend you put enough fuel in the tank to represent the lowest you would ever expect the tank to be when you come off the track. I know many people carry extra fuel as ballast and since it weighs 6lbs per gallon it is an important factor.

As far as your tires and tire pressure I recommend measuring the circumference of each tire to make sure they are similar. Try to get them within 1/4” in of each other from right to left. To adjust the circumference, increase or decrease tire pressure accordingly. Don’t worry so much about getting them perfect because I doubt you will be mounting up 4 sets of tires and matching them all up into matched sets during the season.

OK, with your helmet on and clothing similar in weight to your race suit (or your actual race suit) you and a friend place the kart on the scales. You will need to have your buddy hold the brake to keep the kart from rolling off the scales as you get in the seat. After you get in apply the brake and make sure the steering wheel is straight ahead. Remember that mark you put on the steering shaft to indicate where straight ahead was after you aligned it? Have your buddy check and make sure it is all lined up. Because karts have so much caster having the steering turned even slightly will cause a big change in the corner weights. Now with the steering straight ahead and both hands on the steering have your buddy record the reading from each of the 4 scales. Make sure they get labeled right front, left front, right rear, and left rear. After that is all recorded, have your buddy hold the brake again while you climb out.

The first thing to look at is the minimum weight. I recommend you setup your kart about 3-5 lbs heavier than the minimum for your class. It would be really lousy to win the race only to get DQ’d for something as simple as the minimum weight. I recommend adding weight only to the seat since that is where most of the weight is (mainly you). If you spread the weight out you will make the kart more difficult to change direction so keep the lead centered to the seat area if you can. Think of it like a figure skater doing a spin. If she keeps her arms in, she spins fast. She puts her arms out she spins slow. You want to be able to spin fast. When adding weight make sure you use at least 5/16 inch bolts with conical washers on the seat side and either double nut each weight or use nylon locknuts and safety wire. WKA now requires all weight to be painted white and any piece of ballast that is over 7lbs to be attached with at least two bolts.

To calculate the front weight percentage, use the following equation:
Front % = ((Right Front + Left front) / Total weight)*100

This will give you the front weight percentage. Again try to shoot for what your manufacturer recommends. If you can’t, a good rule of thumb is 43%.

Look at the front weight percentage and add weights accordingly. If the front percentage is low add weight to the front of the seat. If the percentage is high add weight to the back of the seat. With all the weight attached put the kart back on the scales and repeat the procedure and record the new results.

Now it’s time to look at each corner, are the front corners within 1 lb of each other? Are the rears within 2? Here are a couple of scenarios to help you understand what to do.

Figure 1 Shows a near perfect setup for a 320lb weight class. Here you can see that the front wheels are within 1 lb of each other and the rears are within 2lbs. If you can get this kind of balance you are done.

Figure 2 Shows the front percentage is OK, but the right side of the kart is too heavy. To correct this move some weight from the left side of the kart to the right side of the kart. To keep the front weight percentage correct I recommend picking weights near the center of the seat. If the left side of the kart is too heavy do the opposite.

Figure 4 Shows that some work needs to be done. The front wheels are off by 4 lbs and the rears are off by 5lbs. In this case, of the 4 wheels, the left front and the right rear are the lightest of the 4. This indicates that the chassis is a little twisted or the alignment is not correct. Go back and re-check the alignment to be sure. If it is OK don’t panic. The first thing you need to realize is that kart frames are mass produced and made of steel. That means two things. First it means than even with the tightest quality control a frame can be produced with the kind of balance shown in figure 4. Second, it means that since it is made of a bendable material (steel) you may have tweaked the frame the last time you battled for that championship win, or hit that big curb one too many times, or stepped the rear wheel off in that hole at the exit of the turn, or dropped it the last time you unloaded it from the truck…anyway you get the idea.

OK, like I said there is no reason to panic, frames get bent a little and they can be bent back. There are 2 ways to fix the problem. First and by far the easiest way is to adjust the front spindle height. This is done by removing the long bolt that holds the spindle in the yoke and moving around washers. In the case of Figure 4 the left front wheel is light so you need to lower the spindle in the yoke. To do that you need to put more washers above the spindle than are below the spindle. In the case of Figure 5 the opposite is true.

The second way to fix such a problem described in Figure 3 or 4 is to try to bend the frame back to where it needs to be. For some smaller diameter tube frames (30mm or smaller) this technique generally works. For larger diameter frames I have not had so much luck, but your results may be better than mine. To do this I usually put a couple blocks of wood under the wheel that is too heavy and then carefully jump on the waist of the frame. Be careful not to jump on the tie rods as you will be doing an alignment again. You also need to be careful to not fall on your butt and hurt yourself. You will find you really don’t need to jump with both feet just one foot firmly applied will usually do the trick. After each ‘jump’ re-scale the kart. From the results you will get the idea of how much weight you need to out into it. If that technique doesn’t work or doesn’t completely work move the spindles around as described above.

Finally, if you are like me and just barely make weight with zero weight on you get to do it the long way. You see if you are like me and weigh 200lbs you do have a bunch of weight to move around. The only problem is you have to reposition the seat to do it. I recently scaled my new kart and the right side was 5lbs light compared to the right side. I remounted my seat 1/2” in to the left and rescaled it. Even though it took an extra 2 hours, everything was right on when I put it on the scales again.

In the end you have your kart all aligned and properly scaled. Make sure you take your time and recruit a buddy to help. It will take some time, but be assured it will pay off big on the stopwatch.

TOO MUCH GRIP

Fri, 3 Dec 2010 10:39:26 -0500

Have you ever been at the races on a really hot day with a lot of karts to race against? Ever try to deal with too much grip? Yes, that’s right too much grip. It shows up as understeer or push and it happens more often than you think. On the regional and national level, it happens quite often and even at the club level, when there are a lot of karts on the track and the conditions are right, you can have more grip than you know what to do with. Dealing with it is not as simple at you might think, but I will try to give you some pointers to help free it up.

First this situation is somewhat inherent to the design of karts. Most of all it stems from the solid rear axle which defines a racing kart. In order to make a kart turn you need to unload the inside rear tire so the front tires can steer the kart. If you don’t unload that inside rear tire the 2 rear tires that are linked together with the axle simply overpower the fronts and push the kart forward. This is the fundamental story of a kart. It inherently has a tendency to understeer. The more grip you have the more the tendency is.

So what do you do without it? You need to find ways to unload that inside rear tire. Of course like everything there are multiple ways to do that. Since the problem originates at the rear I recommend to start there first. These are the things I would try in order of severity. That is, the first on the list is the smallest change and the last is the biggest change. You will need to choose what is best for your kart by doing some experimenting.

1. Loosen the rear horizontal bar at the rear bumper. Don’t remove it as that would be against the safety rules, but simply loosen the nuts holding it on so that you can wiggle it a bit. This will reduce the stiffness of the rear frame and allow the rear to flex more helping that inside rear tire to unload more.

1. Remove the rear torsion bar and side bar if installed. Again same as #1 we are trying to get more flex in the rear of the kart.

1. Widen the rear track out as much as possible. This change will reduce the amount of weight on the inside rear tire giving it a better chance of unloading.

Click for more info on track width

1. Change to shorter rear hubs. The idea here is to allow the rear of the chassis to flex more. The axle is part of the stiffness of the frame and the longer wheel hubs just add to the stiffness of the axle. Putting shorter hubs on will allow the axle to flex more.

1. Unbolt the 3rd bearing. The idea is to again allow the rear of the kart to flex more. By loosening the 3rd bearing support you take the inside frame rail out of the equation and the chassis will flex more. When you do this you don’t need to remove the bolts completely. Just loosen the nuts and bolts until the cassette can wiggle relative to the bearing hanger. If your kart design does not have bolts that go through the cassette with nylon locknuts you can use zip ties to hold the cassette in place. Note: Be very careful when doing this one. The axle will flex more and the possibility of popping a chain becomes greater. Chain adjustment may be necessary. Also you need to make sure you secure the cassette parts. You don’t want the cassette to spin and get caught in something.

1. Finally change to a softer axle. This is the most drastic change and one of the most difficult to do quickly at the track. After some experience with a lot of grip, you might consider doing this one first. It is easier to add more grip to the kart than take it away.

For tips on axles click here

What happens if you have made all of those changes and you still can’t seem to get the kart to turn?

Well if you still can’t get the kart freed up, work on the front. When working on the front you are still trying to free up the rear, but you do it in the opposite way you did in the rear. In the front you will need to add grip. Adding grip in the front to an under steering kart will give the front tires a better chance of steering those 2 big rear tires. Again like the previous list these are listed in order of smallest to biggest effect.

1. Add front torsion bar. Unlike in the rear when we were trying to add flex and therefore decrease grip here we are doing the opposite. By adding the front bar we increase stiffness to the frame, decreasing the front end flex and therefore make the castor that is designed into the frame more effective. This will cause more weight to be transferred off of that inside rear tire helping it to slip.

1. Increase front track. Again the game here is to increase front grip. Increasing front track will make the front end more sensitive to the castor designed into your frame giving the front end more leverage to unload the rear inside tire. Be aware making this change will improve turn in performance but will decrease mid corner grip. This is because moving the tires are further away from the center of the chassis there is less weight on those tires in a turn.

1. Increase castor. This is the most effective way to add grip to the front end. Adding castor will increase the front ends ability to lift that inside rear tire and therefore allow the kart to turn. Of course the negative here is that steering effort will go up causing arm fatigue.

1. Finally one of the most effective ways to reduce grip when there is a lot of rubber is to decrease tire pressure. Lower tire pressure will allow the tire to run cooler and therefore will have less grip. Be careful not to reduce tires below the tire manufacturers’ recommendations. Too low a pressure will be a safety concern potentially resulting in de-beading a tire.

Of course with all of the changes listed you might find a combination that your kart will not respond favorably to. The response usually shows up as a bad mid corner hop. This still is happening because there is too much grip but the hop occurs because the frame is flexing a lot because the tires have so much power and won’t release from the track. The frame winds up and the snaps back into shape resulting in a hop. Common ways to fix this is to change the frame stiffness is some way. Sometimes adding or removing a torsion bar helps get rid of the hop, usually removing helps more often than not though. You also might try to remove seat struts, but in my experience this isn’t always effective.

Now you know what changes to make to the chassis to free it up when you are dealing with a lot of rubber. A lot can be done to help the kart get around the corners. Smoothness is key to going fast when there is a great deal of rubber. The more abrupt you are with the controls, the more likely the chassis will hop and bind up. Be smooth with the accelerator pedal, brakes and steering. Try changing your driving line. You will likely find that moving your line just a few inches closer to the center of the turn or farther away will help free the kart up. Finally try a bit more trail braking entering the turn. Carrying the brake into the corner while you turn the steering will be asking the rear tires to both turn and slow the kart. If you have too much grip, in the beginning, this will be asking the rear tire to do too much work causing them to slide helping you to turn. Of course trail braking is quite an advanced technique and requires considerable practice to get it right. During one of your normal testing days you might want to consider spending time learning the skill. It could come in handy someday.

So on that really sticky summer day at the track when the rubber is so thick that you can’t get the kart around the corner do the following. Remove as much grip from the rear as you can and then if that is not enough add grip to the front. Be smooth and use that trail braking skill you have been working on. With a little bit of practice and these simple guidelines, you might end up in the winner’s circle.

VALVE SPRINGS

Fri, 3 Dec 2010 10:37:43 -0500

We all have that friend who has a thankless job, you always hear about how someone other then them always gets credit for all their hard work. The valve springs in your racing engine are in the same position, but they normally don’t say anything until it is too late. The cam always seems to get all the attention, people are always asking what cam are your running, but never have I heard what springs are you using? Yes, the cam is the most sophisticated part of your valve train, but without the proper valve springs the cams full potential would never be met. If you put too much valve spring in your engine you are just costing yourself horsepower due to increased friction. If you have too little, the engine will run into valve float costing you power and rpm. Having the right balance of spring tension is critical to being competitive on race day.

I understand that you are probably not going to be designing your own valve springs for your race engine. That doesn’t mean that having a better understanding or your valve spring won’t be a benefit. This knowledge can help you more effectively communicate with your engine builder, or even find problems more efficiently at the track. Even though most don’t think of them this way, valve springs are wear components that do require replacement throughout the racing season. Springs take a lot of abuse and replacing them is cheap assurance that your engine is reaching its full potential. At 7000 rpm your springs have to go from being still, to full valve lift, and back to still 58 times in one second. If your average engine speed during a race is 6000rpm and your race takes 10 minutes that is 30,000 cycles!

The purpose of the valve spring is to keep the related valve train components following the cam shaft profile by pushing everything against the cam. At low speed this is relatively easy, but as speed goes up the inertia of the valve train components make this a difficult task. Inertia increased with the square of speed, so this means doubling the rpm requires 4 times the force to do the same job. This is why high rpm valve trains require a lot of attention. Not only because the spring tension gets to be so high, but also because the other components must be stiff enough not to deflect under these high pressures.

Valve springs have 2 major force measurement points when installed in the engine. The installed height and over the nose, or valve closed and valve open force. The installed height is the height of the spring when the valve is not being lifted and is sometimes referred to as seat pressure; meaning the valve is still on the seat. The over the nose or max lift point refers to the spring’s height when the cam has lifted the valve to max lift. The cam manufacture will either give a specific spring and height to install it at or just give the pressures needed at these two points.

Another big consideration of installing a spring is coil bind. Coil bind refers to the spring’s coil being stacked up and touching each other so it can no longer be compressed. This can have catastrophic effects on your valve train and lead to many ruined parts. Always make sure that you have enough room to avoid coil bind and that at max lift you still have about .060” or more of spring travel left.

Spring force is measured in pounds which are sometimes confused with psi (pounds per square inch) which is a pressure. The measurement is the spring’s stiffness or force, so if the spring has 30 lb. of force at the installed height it would take 30 lb of weight pushing down on the spring to make it compress to this height

Most springs have a linear force vs compression characteristic. This means, if the springs height is reduced in half then the pressure is doubled. This makes calculating the forces of the spring for a particular application relatively easy. If you know the difference in length and the change in pressure you can come up with the spring’s rate or pounds per inch. The manufacture will normally call out the spring force at two lengths. So, if a spring has 15 lb of force at an installed height of .9” and 65 lb at 1.150” the rate would be 200 lb/inch. Because:

Change in Force/Change in length= lb/inch
So, 65 lb-15 lb = 50 lb = 200 lb/inch
1.150”-.9” .25”

Now that the spring rate is known from the manufactures rating or what you have measured yourself you can easily apply it to your engine and adjust it as needed. Let’s say your cam calls for 20 lb of seat force instead of the 15 lb that you currently measured at your installed height. At 200 lb/inch 5 lb is equal to .025” of compression (1 in/200 lb=.005 in/ lb). By installing .025” of shim under your spring you can raise the seat pressure by 5 lb to achieve the 20 lb of force. If the over the nose, or max lift pressure is off then the spring rate has to be changed to achieve the desired force and this can only be done by changing the spring itself.

I realize that this sounds pretty complex, but for the most part your cam manufacturer has done all the hard work and can suggest what you need. This means that you don’t have to spend time on the dyno or track finding this right combination. However, it is still recommended that you check the installed, and over the nose pressure to make sure the spring is correct, if it isn’t then this should help you get it back to where it belongs. In a lot of what we do spring shimming is not allowed. Replacing the spring is the only way to fix an issue if you do find your measurements out of spec.

Measuring the spring force is just a matter of force versus length. By measuring your installed height in the engine you get the installed height. If it measures .830” then by subtracting your max cam lift you can get the over the nose height. With a cam lift of .255” this works out to .575” because ( .830”-.255”=.575”). Now that you know the length of the spring when the valve is at no lift and max lift all you have to do is measure the spring force at these two distances and compare them to the cam manufacturer’s recommendation. See the photos on page 27 for the operation of this essential tool.

Engine builders will normally use more complex spring measurement fixtures. This improves on the accuracy, efficiency, and repeatability which are required for serious engine development. For the average racer the small vise style tools are more than adequate.

I know you are thinking, this is all great, but how does it affect my racing? To prove the importance of this I moved over to the dyno to put some data behind all this theory. The engine tested was a middle of the road WKA Animal set up for sprint racing. The testing included a baseline with the standard as raced springs, followed by lower tension and then higher tension springs. The objective was to prove that by going too little or too far with your spring force results in much the same effect, a dramatic loss of horsepower.

The engine had 3 baseline tests ran on it with the normal racing springs installed. All 3 tests repeated within .1hp of each other so this proved the engine was good and stable. The engine was tested in two ways, steady state and accelerated or transient test. Steady state means that the engine was loaded by the dyno to stay at an rpm point for 30sec each. The engine would sit at 3500rpm for 30sec while the dyno measured its power and then would go to 4000rpm for 30sec and record again, and so on up to 7500rpm. With an accelerated test, the engine is swept at a rate of 150rpm per second from 3500rpm to 8000rpm and power measurements are taken very fast while it is being accelerated. The engine never stops at a point; much like when a kart accelerates.

The advantage of a steady state test is it sits at a rpm point long enough for the dyno operator to see what is going on; it also allows the engine to build more heat. The advantage of the accelerated test is it records at every rpm point while it is accelerating, so it doesn’t miss any dips that could fall between the steady state rpm points.

Testing valve springs can be very unpredictable and unstable so using both test methods helps find any issues that could show up. After the baseline power was established the intake valve spring was replaced with a much weaker spring. The original force was 12 lb installed and 62 lb at max lift for both the intake and the exhaust. The replacement spring measured only 5.5 lb installed and 51 lb at max lift. To start with, only the intake valve spring was changed out, this allows the effects of the reduced force to be isolated to one valve at a time. Chart 2 shows what affect it had on the engines power output. Notice the big dip in the curve at 7000rpm, this occurs because the valve is not following the cam correctly due to the reduced pressure. Remember how I said the power is unpredictable by 7500rpm? The power comes back during the steady state test. Because the karts we race only have one gear ratio, when the power drops like this chances are the kart will stop accelerating and never make it to the point where the power picks up again. On the track this would be a very flat engine, it would feel weak above 6500rpm.

Valve float like this normally has a rev limiter type of an effect. It even sounds similar to a rev limiter at times. The engine’s exhaust note will change and sound hollow, the engine will stop revving, and the carb will show excessive spit back. By the time valve float has gotten to this degree, power has probably been falling off many RPM’s before this. If your engine isn’t acting right listen for these symptoms to help diagnose a bad spring.

During the accelerated test with the reduced force intake valve, the power was also down in the mid range. (Chart 3) Most of us know the term slapper cam when it comes to the Raptor engine. Because in most classes the cam profile and lift are limited by class structure, total power output is also limited. However, if the optimum profile and spring pressure are used, the engine can actually make the cam look much bigger by throwing the valve off the lobe in the region of max lift. This maximizes the power above what is normally limited by the rules but the cams still fall into spec when measured in the tech barn. This is different than loosing control of the valve train like seen here. Most of the “valve float” problems don’t originate over the nose of the cam but actually come from the valve not closing correctly. The valve bounces off of the seat at closing and interrupts the next cycle of the engine. Remember that the valves job is to seal the chamber when shut, obviously a bouncing valve can’t effectively do this.

For the next test the weak valve spring was switched over to the exhaust side. Spring pressure now measured 12/62 lb on the intake and 5/51 lb on the exhaust. The results for this were so low that I reran the standard test again and came back to it to prove that the test was accurate. Anything after 3500rpm showed up as a dramatic power reduction. Though I am not a valve train dynamics expert, I do have a theory as to the differences between the two tests. When the intake valve is closing, the piston is on its way up during the compression stroke, this would create pressure and help the valve stay closed and minimize power reducing bounce. On the contrary, when the exhaust valve is closing, the piston is descending in the bore to induce the intake charge. So, instead of a pressure helping close it, now there is a vacuum helping induce the bounce.

*This sparks the thought that power might be had by staggering the intake and exhaust spring force to achieve the optimum balance between the two. This may warrant more dyno time to investigate the possibility of a “legal” power increase.

This makes it pretty clear that insufficient spring force isn’t going to put you into the winner circle. On the other side, what happens when an excessive amount of spring force is used to guarantee that you don’t see this power robbing valve float. To answer this question the engine had springs designed for a modified engine installed. In this situation higher spring forces are necessary because of the higher valve accelerations and increased engine speed. The intake force now measured 52.5 lb installed/ 94.5 lb over the nose, and the exhaust measured 51 installed/93.5 over the nose. In theory, running too much force will cause undo wear on the valve train, and most importantly an increase in friction. Unneeded friction is a waste of valuable horsepower. As you can see by Chart #6 the power loss is no insignificant amount, it is enough to dramatically affect your on track performance. The frictional power loss increases with engine speed until it reaches a point where the higher spring force starts to become more necessary and the loss start to taper off. The peak power loss was .4hp, or looking at it another way you could gain .4hp by getting the springs right.

This is a lot to take in, but remember this was an extreme example to prove out the theory. Simply put, running too much or too little spring force can both affect your engines performance negatively. Get it right and your engine will spin freely and still make maximum power. Remember that the cam manufacturer and engine designer have all worked this out so you don’t have too, unless you are doing something custom, listen to their advice and you are almost guaranteed success. Use this knowledge to help hear what your valve springs might be telling you or to set up your new springs and it may save you a race some day.

AXLE INSTALLATION & REMOVAL

Fri, 3 Dec 2010 10:29:30 -0500

We’ve all been there: taking the biggest dead-blow hammer available and beating the living tar out of an axle to try and remove it from a kart. And we’re not talking about a crash bent axle either we’re talking about trying to change a straight axle for tuning purposes. So why is it so difficult to remove and install an axle sometimes? Is there something wrong with your kart or your procedure for installation? Or is this just “part of karting?”

Changing an axle should not be able to be counted as a cardio workout. At a recent 2009 Kart Product Launch, we were amazed to watch the Italian “super-tuners” change an axle in eight minutes from the time the kart stopped to the driver launched back to the track! According to the manufacturer, this amazing feat was accomplished because “the axle was put in right the first time.”

Installing an axle properly before you leave for the track is something that will take a little time to do in the garage, but will pay huge dividends at the track when it’s time to change the axle. In the remainder of this article we will go through the proper steps to remove and install an axle, provide tips for making axle changes more time efficient, and help troubleshoot an axle that is being difficult to remove or install.

Why changing an axle requires a large rubber hammer:
In a perfect world, changing an axle would just require the removal of the bearing set screws, the removal of the wheels and hubs, and the loosening/removal of the brake rotor carrier and the sprocket carrier. Everything else (bearings, cassettes, cassette hangers, frame) would be perfectly aligned and free enough to shove the old axle out one side of the chassis. Often –no, rarely, does that happen.

There are a number of reasons an axle doesn’t just slide out. Most often, something is “bound up”. In other words, something isn’t straight causing the already tight tolerances between the axle and the inner bearing races to be even tighter. Questions to ask oneself about why an axle would be bound up include: was the rear of the kart crashed since the last axle change or are the cassettes equally torqued in the bearing hangers? It only takes one cassette bolt that pulls the bearing hanger and cassette slightly from the straight position (perfectly perpendicular to the axle) to bind the axle up.

A way to check for axle bind before trying to remove the axle is by installing a minimum number of bolts in the cassettes, say two each, lightly torquing them and spinning the axle. Provided the bearings are good (and that’s a whole other story) the axle should spin freely and easily for a few revolutions. If the axle is spinning free, properly torque the cassette bolts and install the remaining bolts one at a time checking the free-spin of the axle between each.

One other piece that binds quite often is the brake rotor and its carrier. The brake rotor creates immense heat while in use, and this heat is transferred down into the axle causing the two to seize slightly. Also, the load (twist) a rotor puts on an axle under braking can essential ‘pre-load’ the axle/rotor carrier causing bind. Two simple tips to try and reduce the seizure and eliminate the bind are to use a thin layer of anti-seize lubricant between the axle and rotor carrier. If it’s difficult to slide the rotor and carrier when the carrier bolt is loosened, try loosening the actual rotor from the carrier.

Another reason an axle might require a hammer to uninstall is the over-tightening of the bearing set screws to the point they dig into the axle causing burrs or flat spots (crush points). “Burrs are the big one, not just from the set screws but also from around the recesses around where the keyway goes,” says Mark Ouimet, from SSC East. “I keep a small file near by to file down set screw burrs while the axle is being removed.”

No one wants their axle to shift while on track, but it also doesn’t do any good damage it for future use. In reality it doesn’t take much torque for the set-screw to hold an axle in place. Instead of over torquing an axle set screw, try using a drop blue Loc-Tite to assure the set screw won’t back off.

“Another reason we see for straight axles being difficult to remove are the ends of the axle being ‘mushroomed’ from being beaten in or out and excess plating on the axle,” states Keith Freber owner of Margay Karts. “When removing or installing the axle used a soft faced mallet (if necessary). If you take your time and do things right, you shouldn’t need a hammer at all. Take special care with thinner wall axles. It’s very easy to distort the ends.”

However, there are certain times you need the soft-mallet and there are other times that the axle stops moving at the bearing without the axle being able to slide out. There are tools to move the axle outside the bearing. “In the past I have taken old bent axles and cut off a six inch section from the straight section,” continued Ouimet. “Then while getting a axle out if I get to the bearing I can use this piece that I have cut to push the axle through the remainder of the bearing.”

Install It Right the First Time:
Now that we know a couple of the reasons why an axle is difficult to remove, we need to understand what we can do during the install process to make changing an axle easier in the first place. With axles becoming more and more important in the tuning process, it’s becoming essential to be able to change them between on-track sessions not just at the end of the day.

As was stated earlier: if an axle goes in straight the first time, it should come out straight and easy. There are some general assumptions that need to be made before going any further with this article; we must assume the axle and the frame are straight. If either is even the slightest bit tweaked, skewed, or bent that could result in the binding affect that is encountered during installation and removal.

Click for more info on rear end adjustments
Freber reiterates the importance of “pre-installing” a new axle before leaving the garage to make it easier changing at the track: “Install the axle, tighten the set screws just enough to mark the axle, remove the axle and file a small flat where each set screw makes contact. Be sure to re-install the axle with the set-screws properly aligned.”

At this point, the axle of the kart is removed so there is no better time to clean the chassis and prepare the bearings for the new axle. “Clean, Clean, Clean while the axle is out it is a perfect opportunity to clean up the back end. Check for any imperfections, burrs in the bearings that the axle may get hung up on,” states Ouimet. One effective way to prepare the bearings and assure they are free of burrs is to use a ball hone on the end of a drill. Ball hones can be purchased in about any diameter from many industrial supply stores and specialty tool shops. Fifteen minutes with the ball hone and some WD-40 can assure the bearings are clean of burrs and of the correct diameter for the axle.

As mentioned in an earlier paragraph, sometimes the plating on an axle increases the diameter more than the manufacturer intended; this also happens on the inside diameter of the bearings. To reduce the thickness of the plating, even a ten-thousandth of an inch, karters may be required to use Scotch-brite or another very fine abrasive on the axle. “Make sure there are no burrs in the bores of your hubs. Pay close attention to the edge of the key slot,” says Freber. “Clean the bores with WD-40 and Scotch-brite.”

Once you are assured the bearings and axle are free of burrs and the diameters of the axle and bearings are correct, it should be easy to reinstall the axle. If the chassis has a third bearing, loosen that cassette for installation. Test-install the axle through the inside, third (middle), and outside bearings; assuming it slid in and out freely it’s time to try and install it with the brake rotor.

Often, when the brake rotor and carrier are added to this equation is when the axle becomes more difficult. Some tuners suggest loosening the rotor from the carrier; if you choose to try this –be sure to tighten the rotor back up after the installation is over. Another option to assure the brake rotor fits properly is to again check it for burrs on the inner diameter and use a lubricant such as WD-40 to make installation easier.

Something else to remember when installing the axle for the final time before hitting the track: don’t forget the brake rotor key or the water pump o-rings (if applicable). No matter how many times a mechanic has changed axles, every now and then even the best forget the brake rotor key or o-rings.

Now let’s look at proper axle installation in a step-by-step manner. We will begin this process with the axle free of burrs, clean, and out and the bearings and rotor/sprocket carriers cleaned and honed (or polished free of burrs).

1. “Loosen the third bearing before removal or installation,” states Freber. “And only tighten it after you have tightened the set-screws in the two outer bearings.” Additionally, consider only having three of the outside bearing carriers bolts installed in each side. Some carriers now come with up to six mounting points for added tuning; if you desire more than three, they should be installed later (see step eleven).

1. Lubricate the inside diameters of the bearings and rotor carriers either with high-temperature assembly grease, anti-seize, or a generous flow of WD-40. “It is common to use a lubricant on the axle when removing it, don’t forget to leave a spot “unlubricated” so you will have a spot for a good hand hold,” stresses Ouimet.

1. Insert the new axle from the engine side through right side and third bearings. This should be rather easy, especially with the third bearing loose.

1. Install water pump o-rings if applicable.

1. Position brake rotor in caliper (double checking the direction of the rotor as this matters for proper key placement with some axles).

1. Continue guiding the axle through towards the brake rotor carrier and gently begin to push it through the rotor carrier. It may be easier to turn the axle as it goes through the carrier to help assure it goes on straight and not slightly cocked at an angle.

1. Align and begin to move the axle through the left side bearing. If excessive force with a rubber mallet is required at this point, chances are there is an alignment issue (slightly bent frame, ride height difference, etc.) that requires immediate attention.

1. Don’t forget the brake rotor carrier key!

1. Assuming the axle is through all three bearing carriers, rotate the loose axle to align the previously made (see above) flat-spots for the set-screws. Also, at this point the axle needs to be measured from each outside bearing to the axle tip to assure it’s centered in the chassis.

1. With the axle centered, it’s time to install the set-screws in the outside bearings. Using a drop of blue Loc-Tite, install and tighten all the outside bearing set-screws –but don’t over tighten them and damage the axle!

1. With the outside carrier set screws in place, it’s time to tighten the third bearing if applicable. Tighten the third bearing carrier bolts, one at a time, while spinning the axle to assure no bind is being added to the chassis. Also at this time, if you desire more than three bolts to hold in the outside carriers add them one at a time. Be sure to keep checking the axle’s free-spin to assure none of the addition bolts are adding bind.

1. Install the third bearing’s set-screws (if desired) in the same method as step 10.

1. Center and tighten the brake rotor carrier.

1. Double and triple check the axle spins as freely as it did when it was just slid through the two outside bearings!

Reducing drag in the axle is like adding horsepower to your engine, and usually a lot cheaper and easier. Proper axle installation is essential for minimizing drag and for ease of removing the axle –one of the strongest tuning tools karters have at their disposal. Possibly the best a karter could take regarding axle installation comes from Freber: “Take the time and pre-install all of your axles. This should help you avoid the embarrassment of asking your pit neighbor for a larger hammer!”

Click for more info on track width

AXLE KNOWLEDGE

Fri, 3 Dec 2010 10:26:29 -0500

There was a time when kart axles were pretty much all the same. Initially 1” in diameter and solid, axles eventually evolved into 1 1/4” and then, briefly, 1 3/8” tubular materials. The gains in torsional stiffness and flex control took advantage of emerging tire technology and opened the door for tire manufacturers to develop tires with even greater performance capability.

Since then, axles have not only continued to get larger, 40mm and now 50mm, but an entire subset of axles has emerged. Axles are available labeled “Hard,” “Medium,” “Soft,” “Extra Soft,” and “Extreme Soft.” Couple that with Short, Medium, and Long rear hubs and you have 15 different combinations to try, each with its own performance characteristics. For the less experienced tuner, it can be a bewildering process. Let’s look at each factor and how they affect chassis performance.

Axle manufacturers can tailor the dimensions and materials of their axles to provide a wide range of characteristics. The 2 biggest concerns to the tuner are torsional stiffness and beam deflection. Torsional stiffness is defined as the resistance of some element, in this case a tubular axle, to twisting between any 2 points along its length. In a karting context, it is the force required, for example, to twist the axle under braking between the brake disc hub and the rear wheel hubs. Beam deflection is the bending of an element, like an axle, by applying some linear force, up, down, forward, back, or any combination, perpendicular to the length. By varying the steel alloy, the heat-treat tempering, and the wall thickness of each axle, they can deliver axles with a wide range of flexibilities, both torsionally and in beam deflection.

For most karters, the torsional stiffness of their axle is of little concern. The higher speed and higher weight machines might sense some improved stability under braking with a stiffer axle, but in most cases is will be undetectable. Beam Deflection, however, can be part of every chassis tuners bag of tricks. John Kozubik of Kart Warehouse reminds us that the driver and engine on a kart are the “sprung weight” and represent the majority of the mass that goes across the scales. How that “sprung weight” puts leverage on the chassis and how the chassis responds to it is what determines how the kart handles. Let’s imagine, for example, that you are entering a medium-speed right-hand corner. As you turn the steering to the right the caster and other front-end geometry jacks weight to the left rear corner of the kart. Some of that force wants to “roll” the chassis to the left, putting a great deal of pressure on the left rear tire as it compresses on the track surface. The softer the axle is the more of that force gets absorbed in axle beam deflection. This lets the right rear tire unload even more without overloading the right rear. This makes the kart “looser” in the back and induces more oversteer. Conversely, a stiffer rear axle absorbs less of the beam deflection force and transmits more force to the left rear, making it “bite” more, making the kart “tighter” with less oversteer.

Click for info on exit oversteer

But, hey, doesn’t this do exactly the same thing as moving the rear wheels in and out? Well, sort of. Moving the rear wheels in and out does change the nature of the understeer/oversteer equation, but in a different way. Moving the rear wheels out changes the angle that the force from the chassis exerts on the contact patch of the tire without changing the amount of that force. Changing the axle stiffness increases or decreases that force without changing the angle of the force. The results are similar, but the feel is entirely different. Some drivers describe the change in axle stiffness as more “transitional.” Changing from a harder to a softer axle may help the kart rotate into the turn with less understeer while not sacrificing grip from the middle of the turn to the exit. In contrast, widening the rear track, while it might help initial rotation, reduces grip throughout the turn and might induce oversteer. Mark Dismore Jr. describes it this way:
“Adjust the rear width to get the kart to feel the way you want, then use axle stiffness and hub length to get the level of grip you need.” It’s a tricky balancing act, but the dedicated and well-prepared tuner can get the best from using both adjustments.

One more thing about axles: what’s better, 40mm or 50mm? That’s the subject of plenty of debate. Lots of chassis manufacturers and their dealers will tell you that 50mm axles are dramatically better than 40s. Certainly there are karters out there winning at the highest levels with 50mm axles, but are they winning because of the 50mm axles, or would they be winning anyway because they are on the latest and greatest rides? From a materials standpoint, it shouldn’t matter if the axle is 40mm or 50mm. There are tiny torsional stiffness increases in a 50mm tube versus a 40mm tube of the same wall thickness, alloy and temper. And, again from a materials standpoint, there isn’t anything in beam deflection stiffness that the manufacturers can do with a 50mm axle that they can’t do with a 40mm one. Experienced racers have reported that the larger axles ride a bit smoother, particularly over bumps. Most likely the 40mm vs. 50mm debate is like necktie widths or skirt lengths. It’s hot, it’s trendy, and it sells more new karts. That’s not to say that the new karts, with their 50mm axles, aren’t better than the older karts. Improving technology and development makes everything better, including karts. But it may be that the 50mm axles are not what make them better.

Related Articles
Axle Installation & Removal
Too Much Grip
Rear End Adjustment

Earlier we mentioned rear hub lengths as a tuning tool related to axle stiffness. How does that work? If you think about the axle being able to deflect between the bearing and the point where it is encased in the hub, then you see that you can change the effective axle stiffness by moving the hub in or out. Moving the hub in makes the axle effectively shorter and, thus, stiffer. Moving out makes the axle effectively longer and softer. But what if you want to stiffen the axle slightly without changing the rear width? What if you like the way the rear end transitions between grip and breakaway but you want to move that point a little more towards the grip side of the equation? Changing to a longer rear hub shortens the distance between the bearing and the hub, making that part of the axle effectively stiffer, without changing the location of the contact patch of the tire and the resulting force angle acting on it. Pretty nifty, huh?

Finally, a word about axle materials; right now WKA mandates that axles be made of steel alloys. And as we said, most manufacturers produce axles of varying stiffness by adjusting the alloy, temper, or wall thickness of the tubes. But at least one manufacturer is using thin-wall tube axles with changeable inserts to adjust the stiffness. Another manufacturer is promoting carbon fiber composite axles using the same insert approach to change stiffness. Be sure to check with your local sanctioning body to make sure you don’t invest in an axle (or axles) that you can’t legally run.

Properly used, different axle stiffness and different rear hub lengths can be another valuable tuning tool for the karter intent on getting the most out their set-up. But, as with so many things, just buying the pieces and trying them “on the fly” won’t get you very far. The best approach is to devote plenty of dedicated testing time to learn what each change does. You won’t get that kind of time on a race weekend. You’ll have to get out there by yourself when you can commit enough hours to learning what these tools can do for you. Once you have a grip on how each change affects your kart’s handling, then you can use them on race weekends to put your very best package on the grid. See you next time.

GEAR RATIOS

Fri, 3 Dec 2010 10:24:03 -0500

Gearing a kart is an issue that many new karters don’t try to deal with. Most people will ask around the local track to see what everyone else is running and run that gear. However, what if you are testing at a new track and don’t have any locals around?

Moreover, how do you know that the gear they give you is really the optimum one for your situation? This month I am going to review some rules of thumb based on my experience, which will give some insight on the task of establishing the optimum gear for a kart.

The first thing to remember, obviously, is the goal the whole exercise is to obtain the minimum lap time. It is not necessarily trying to get to maximum RPM at the end of the longest straight. Depending on the track, the gear that gives maximum RPM at the end of the longest straight may not give the minimum lap time. I’ll get back to that point later.

First, some background. Let’s assume a dyno pull shows that peak torque for the engine we’re gearing is about 10,300 RPM. Although it does not officially have a redline, we will use 15,000 RPM as our redline figure.
Also, when you are running a gear test you need to have the carburetor tuned for race conditions and be sure to keep in tune with race conditions throughout the test. The test will still work with the carburetor set a little rich as long as it is consistent during the test, but the closer to optimum setting the better the test will be. Pick a point at the end of the longest straight to look at your RPM gauge (preferably on the data download to assure consistency).

Remember, if you are looking at peak RPM for each lap there will be some variation as the peak RPM is dependent on the RPM at the beginning of the straight: the more RPM at the beginning of the straight the more at the end of the straight. This is why many beginning karters find themselves dropping down to smaller gears as their driving skills improve. While a beginning driver might find that a certain gear gives a good maximum RPM number on the straight, an experienced driver might come on to the straight with more RPM and find that the same gear gives them too much RPM at the end.

So pick a gear, based on another similar track or a local recommendation and run some laps. Let’s say that the maximum RPM at the end of the longest straight is 14,300. Next, drop two teeth and try the test again. The reason I say to always drop teeth is because the biggest error I see is running too big of gear. Contrary to what you might think, running a bigger gear does not always result in increased RPM. I have found through experimentation that if the initial gear selection is way too big (defined as approximately five teeth more than optimum) most engines will not pull more RPM. In fact, going to a smaller gear can cause the RPM to increase.

The concept of a larger gear not allowing for more RPM at first blush seems incorrect. Remember that we are talking about a starting gear that has been incorrectly selected and is about 5 teeth bigger than optimum. The explanation involves the horsepower curves of the motors. All kart motors achieve their maximum horsepower at less RPM than they are capable of running. The higher you try to rev the motor the less the horsepower. Think of the horsepower it takes to maintain 60 MPH. If it takes 15 horsepower to run at 60 MPH and you are geared to be at an RPM (higher) that gives you 14 horsepower at 60 MPH you obviously won’t achieve 60 MPH thus not reaching as much RPM. You can prove this to yourself by adding 3-5 teeth to your normal gear and seeing the affect.

Click for gear ratio chart

When in doubt as to add or take teeth off: always drop two teeth. As a rule of thumb, I look for a decrease of less than 200 RPM per tooth when reducing teeth or an increase of less than a 200 RPM per tooth when adding teeth when you have made the right choice.

There is a trade-off involved with gearing. The lower the gear, the closer you are running to the peak torque number. However, the bigger the gear the better the acceleration off the slow corners. The layout of the track will define the optimum maximum RPM. For example, at a relatively fast track here in the northwest, our best lap times correspond to a maximum RPM of 14,700. We have found if there are no tight turns to slow the engine down than it is best to operate a little closer to the peak torque number. At another, tighter track, our best times correspond to a maximum RPM of 15,300. At the tighter track we allow our maximum RPM to get farther away from the peak torque number in order to pick up some acceleration off the slow corners.

To recap, pick a gear and drop two teeth. Keep dropping two teeth until less than a 400 RPM drop is recorded. Play with that final gear plus one tooth to figure out which gives the optimum lap time. If the first two tooth drop results in less than a 400 RPM decrease, be sure to add two teeth to the original gear to be sure that original gear was not too small. If that increase results in less than a 400 RPM increase than the original gear was close. Try it plus and minus one tooth to find the optimum lap time.

EXIT OVERSTEER

Fri, 3 Dec 2010 10:23:08 -0500

One of the most common problems I encounter at the track while driving my equipment, watching others drive, and while helping others tune their chassis is an oversteer off of the exit of the corner. It often makes applying throttle at the apex a difficult task and zaps valuable forward thrust that is needed to propel your kart down the following straightaway. In this article I will discuss theories pertaining to the causes of an exit oversteer as well as several other aspects of the condition.
As a driver coach at BeaveRun in Wampum, Pennsylvania I work with many young and developing drivers. One of the biggest hurdles developing drivers face is how to establish what are good chassis handling characteristics and what are not. Confusion often results from what might be a very comfortable setup and thus easy to drive for a driver who is not 100% confident. From my experience comfortable almost invariably means a kart that is too “tight.” I like to define “tight” as a chassis that gives the perception of having a greater proportion of rear grip than front grip and as a result is not balanced.

One common outcome of a tight chassis is an understeer. Understeering karts tend to be more predictable under braking and may inspire more confidence through high-speed corners. However, understeer often results in a snap oversteer off the exit of tighter corners which can destroy speed entering straightaways.

In this scenario the cause is the entry understeer and the effect is the exit oversteer. In karting circles this is often known “push-kick” or “push-whip.” The most common theory, and the one that I personally subscribe to, says that the entry understeer prompts the driver to increase the amount of steering angle to compensate for a chassis that is not approaching the apex at a quick enough rate. At some point in time after the steering angle is increased the front tires achieve enough load or slip angle to turn the kart. However, the wheels are now at a greater steering angle than should be required for the turn. The instance that grip is achieved happens very quickly. The final result of this quick increase in steering traction is a snapping or whipping of the rear end of the kart or what I am calling an exit oversteer.

It has been established that the effect is an oversteer and cause is the understeer. So in theory if we correct the cause we will also correct the effect. Effectively, we should be able to kill two birds with one stone. I must also note that fixing an entry understeer is done differently than correcting an exit understeer. Keep in mind that an exit oversteer can exist on its own with different causations than we are discussing here.
Related Articles
Axle Knowledge
Axle Installation & Removal
Too Much Grip
Front End Adjustment
Rear End Adjustment
Before going straight to chassis adjustments I will also say that my own tuning strategy is based on what I call “123 ABC theory.” Practically speaking, if you get the kart right in the first part of the corner then it is more likely to perform correctly at mid corner and apex. If the kart performs correctly in the first two parts of the corner then it is again more likely to perform correctly in the third and final part of the corner.

One final thing, before I make changes to the chassis setup I like to evaluate overall chassis neutrality. For this I evaluate the karts current setup and decide if the kart is currently set to any adjustment extremes. An extreme for me includes low rear ride height, really high or low castor settings, and extremely stiff or extremely soft axles. This list will be different for just about everybody and it is important to note that some chassis will be setup towards extremes a lot of the time. Many Yamaha Can class karts are good examples of this. Use my list only as a consideration of potential areas of chassis setup that might represent extreme outliers and as a result could be obvious causations of an entry understeer or any other handling ailments you may come across.

At this rate you probably thought I was never actually going to get to chassis setup. An entry understeer is 99% of the time is the result of a kart that is not able to transfer weight quickly enough. Take this literally. All the evidence I have collected says that a kart begins the initial turn-in sequence on the inside front tire. This is a direct result of the castor built into the front-end geometry of the chassis. Simply put, if weight is not applied in great enough quantity or instantaneous enough to the inside front tire an entry understeer will likely exist.

For the “newbies” out there I will give a quick explanation of castor and its application to kart dynamics. Castor angle as well as scrub radius causes the inside front tire to drop and the outside front tire rise when the steering wheel is turned. This is due to the castor angle or the leaning of the top of the kingpin towards the rear of the kart. This effect is often called “jacking.”

Ultimately this means that at the instance the steering wheel is turned a percentage of weight is placed on the inside front tire and a large percentage of weight is removed off of the outside front tire. Furthermore, if the steering wheel is turned and weight is not being added to the inside front tire at a fast enough rate or in great enough proportion the chassis will understeer. For practical purposes I will ignore factors like weight distribution in this discussion as that factor would add thousands of words to the article. Suffice it to say however, more often than not more front weight increases the rate at which the chassis will turn initially. Ignoring weight bias there are several other options to increase the karts ability to turn-in and reduce entry understeer.

The biggest of all adjustments would be the addition of castor. This means leaning the top of king pin further back. This increases the rate at which the inside front wheel drops as well as the rate at which the outside tire rises. The results being a quicker weight transfer onto the inside front tire and in increase in the karts ability to turn-in. Increases in positive camber can also help increase turn-in. Positive camber involves the movement of the tops of the front wheels away from each other. Increasing positive camber means that at turn-in the inside front tire, the one turning the kart in, has a greater lean towards the apex of the corner. This is the same principle as leaning a motorcycle. Leaning the tire towards the apex produces what is known as camber thrust and actually causes the tire to drive towards apex without additional steering angle.

Front torsion bars can also help. Putting the front torsion bar in stiffens the frame across the front of the chassis and creates a more positive or efficient transfer of “weight jacking.” Another adjustment to look at is front width. Increasing front width increases scrub radius. Scrub radius is the distance from the center of the wheel to the center of the kingpin bolt. Speaking simply, the greater the scrub radius the greater the jacking effect. This works very much the same as increasing castor angle. However, on some softer chassis increasing front chassis width might actually have the opposite effect. This can be attributed to the relation between increase in scrub radius and the resulting increase in leverage that the wider width puts on the chassis. Greater leverage can create the symptom of what boils down to the softening of the chassis and thus may negate the added jacking effect gained by greater scrub radius. I mean this in a mechanical sense not in the terms of actually softening the materials the chassis is comprised of. As far as front width is concerned my experience says the majority of 30mm and 32mm chassis will turn-in quicker with greater front width while some 28mm chassis might actually turn-in better with a narrower scrub radius. Testing will establish this for your given chassis but generally the rule above appears to hold true.

For finer adjustment I may attack the rear width. Narrowing rear width can have the effect of making weight jacking slightly easier. This is due to several factors. A narrower rear track has less leverage over the front of the chassis and thus making weight transfer easier. Moreover, a narrower rear track effectively raises overall center of gravity, which can help unload the inside rear tire and allow the kart to turn. Rear track adjustment is a small tuning tool when considering turn-in. I recommend using it as a fine-tuning tool.

There is a lot of information in that paragraph above so I would like to boil all of it down to a few main points. Castor adjustment may create the biggest change to the karts turn-in characteristics. Front width is a finer adjustment but is where I recommend starting if castor is seen as too big of an adjustment. Camber is a good tool also and I have found it to be highly effective in “green” track conditions but be aware that camber adjustments have many side effects in other parts of the corner. The front bar is always a solid choice but again be aware of the side effects. Rear width is effective for small adjustments to turn-in characteristics but narrowing the rear can be detrimental to the braking stability of the chassis.

We got through the most common cause of an exit oversteer but there is at least one other scenario that has not been discussed. This scenario is far less common but I do come across it from time to time and find that it is especially frequent in rain conditions. One of the goals to going fast in a kart is unloading the inside rear tire. This inherently means that you are turning on one rear tire. Sometimes the rear tire remains unloaded for too long. Yes, it actually can happen. If it does occur it can result in a kart that has a tendency to exit oversteer. Usually a good characteristic of this scenario is that the kart turns-in correctly but once you apply the power the kart rotates excessively. The bottom line here is that you are attempting to turn and accelerate forward on one tire. The basic strategy in this situation is much the opposite of the strategies I presented for the “push-kick” scenario. In this situation you are looking to set the inside rear tire down a bit sooner. Once you get both tires on the ground you will find that you no longer have oversteer. This however is a fine line to walk. You need to set the tires down just enough so that you eliminate the exit oversteer and gain forward traction but not so much as to “bind” the chassis up.

The theory being applied is the reduction of weight transfer. Remember however that we are attempting to go in small adjustments because an exit oversteer is leagues better than an exit understeer. Slight decreases in castor through either direct adjustment of castor or through reduction in scrub radius (reduction in front width) are obvious adjustments to try. Slightly lowering weight transfer through a slightly wider rear width (effectively lowering the center of gravity) can help get your inside rear wheel back on the tarmac a bit sooner. If the exit oversteer is extreme then lowering the rear ride height may also be a step in the right direction. Very extreme over transfer conditions can be customary with taller and bigger drivers who may have relatively higher mass.

Again I will review the adjustments and try to sum them up in terms of usability. Castor can be adjusted in large or fine adjustments depending on the adjustability of your specific chassis and can help fix the problem immediately if adjusted correctly. Front width is a smaller adjustment and as a result is less risky. If the exit oversteer is small then start by narrowing the front width by a spacer. Rear width is a fine adjustment and by going a touch wider that last little bit of exit stability might be found. Rear ride height is a big adjustment in my experience. If you are feeling like the kart has more than enough mid-corner grip but is exit oversteering badly this is a good adjustment to try. Before using any of these adjustments one must always consider possible side effects of each chassis change and pick the compromise that will maximize benefit and minimize negative side effects.

In this article I explained the theory behind two different types of exit oversteer conditions and discussed several potential chassis adjustments. While I find this theory to be reliable and repeatable under most circumstances there are always conditions in which it may be proven wrong. Additionally, there are adjustments that I ignored so as always I recommend that you keep on testing.

FRONT TRACK WIDTH

Fri, 3 Dec 2010 10:17:16 -0500

Front track width is a function of at least four different factors. For new karters, front width is adjusted by moving the wheels in or out on the front stub axles. Changing the width alters at least four separate factors. These four aspects are vertical center of gravity across the front of the chassis, scrub radius, the leverage on the chassis exerted by each wheel, and finally the dynamic change in wheelbase across the inside and outside of the kart when the steering is turned.

For all intensive purposes I am going to flat out ignore the dynamic change in wheelbase. To be honest, I have not fully explored this factor and cannot venture even a guess on how it changes chassis characteristic. For now I will focus on just the first three factors.

By decreasing or increasing your scrub radius through adjustment of overall front width you are also changing the amount of jacking effect created by the front end geometry of your kart. Scrub radius is the distance from the center of the tire to the kingpin bolt. Combining scrub radius with caster angle is what allows the inside front wheel to drop and the outside front wheel to rise when the steering is turned. A chassis with zero scrub radius will have a zero net gain in wheel height change even with excessive amounts of castor. Additionally, a chassis with zero degrees of castor and an infinitely large scrub radius will again experience zero net gain in wheel height change when steering input is changed.

It has been shown those scrub radius and castor angles are both directly related to jacking. As a result, it can be concluded that across a certain amount of steering input the inside front wheel will drop a given amount and that the outside front wheel will raise a certain amount. Through observation of the kart on the stand this jacking effect can be further confirmed.

The amount that each wheel changes height is thus a function of castor angle, scrub radius, and finally kingpin inclination. Kingpin Inclination (KPI) is best described as the angle at which the kingpin either leans towards the center of the chassis or away from the center of the chassis. Other than the previous short blurb I will largely ignore KPI in this article. Suffice it to say that KPI is also very important in controlling the rate at which the wheels raise or drop.

You are probably now wondering how does changing front track width or scrub radiuses alter chassis handling and what might the driver feel when making these changes? As was already demonstrated, wider front track width creates a greater amount of jacking effect across the front of the chassis and narrowing does the opposite. I have found that the majority of the time this creates the feeling of quicker turn-in and conditionally greater mid-corner grip. Theory regarding turn-in revolves around the speed at which the inside front tire drops.

Given the amount of steering input (steering angle) and the speed at which the steering wheel is turned remain constant the inside front wheel will literally drop quicker than an inside front wheel that is set to a shorter scrub radius. Remember that because the inside front wheel drops and the outside front wheel raises it can be deduced that karts must at a minimum create initial turn-in force using the inside front tire.

Practically speaking this should result in a kart that tends to turn-in faster. Moreover, this outcome can to a degree be associated with a slight compounding effect. Not only should increasing scrub radius help the kart turn-in more positively it should also require less steering angle from the driver.

Though, this is where we must consider the increase in leverage exerted across the front of the chassis. Imagine taking a very long lever and lifting on the inside front of the chassis. If the lever is extremely long it will be easy to not only lift that side of the chassis up, but it will also be easy to deflect the frame.

The paradox that karters experience with front width is that as you increase front width you also increase wheel leverage on the front of the chassis. Leverage on the frame effectively decreases the frames ability to translate jacking effect efficiently. At an unknown and completely chassis dependent point the creation of a larger scrub radius to increase jacking will produce quickly diminishing returns. Simply, the point at which any chassis experiences this is dependent upon the almost infinite variables built into each brand. Theoretically, this phenomenon can happen to every chassis though the point at which the phenomenon can occur may be outside of the karts built in adjustability.

Furthermore, narrow front widths tend to translate jacking effect more efficiently into the frame. Keep in mind that wider front widths effectively soften the chassis. To make this situation more easily understood here is a theoretical explanation. Imagine a chassis that is 100% stiff. This chassis no matter how much load you place on it will never deflect. Turning the steering will then translate 100% of the wheel height change through the chassis. Now if the chassis is only 5% stiff and the steering is turned the result will be that only 5% of the total jacking effect will be transferred across the chassis. This means that the soft chassis deflects and in doing so absorbs 95% of the jacking effect.

Drivers with experience driving soft chassis, often comprised of 28mm tubing, call the point at which increasing front track width no longer produces greater turn-in “going soft.” This phenomenon can also occur with other stiffer chassis too, though, they are less likely to do so unless you are running very extreme front width settings.

If you have established that your chassis goes soft you may then experience that the kart actually experiences better turn-in characteristics by going narrower. I stress that this in most cases is experienced with very soft frames or when you are running extremely wide front widths. If you find yourself in this dilemma and you feel that the kart needs to turn-in more positively you may need to approach the entry understeer with different devices (hint: narrow the front and add castor).

Related Article:
Front End Adjustment

Finally, we must discuss the effects of center of gravity across the front of the chassis. When we look at a kart and imagine the center of gravity we try to view the point at which the mass is centered around. This point exists in three dimensions. By widening or narrowing the front width we primarily change how the vertical dimension or the height of the center of gravity interacts with the two front wheels. A wider front track in effect lessens the amount of leverage that the vertical center has over the two front wheels.

There are two different theories that I have explored regarding the vertical center of gravity and front width. I believe each theory to be true but to be conditional depending on the characteristics of the chassis at any given time.

The first theory says that karts require weight transfer onto the outside tires to generate grip from the tire. If this holds true then narrowing the front width should gain mid-corner and exit grip. In this scenario the narrow width allows the weight to transfer with greater force to the outside tires.

The other theory says that a wider track lowers the center of gravity allowing the mass of the kart to be carried more evenly across the two front tires. The wider width does not literally move the center of gravity to a lower position but rather lessens the amount of leverage the existing center of gravity has over the chassis. Effectively, this is the same as lowering the center of gravity. Dispersing the mass of the kart across two tires should better than one and once again this theory should increase mid-corner to exit grip. However, this relationship is a bit more complicated. Remember that wider scrub radius also increases the rate at which the inside and outside wheels change height. As a result you get an effectively lower center of gravity and a mechanical situation (weight jacking) that also places weight on the inner front tire at a greater rate. Further, if you increase track width very far and as a result increase jacking to an extreme you may experience a paradoxical effect where the mechanical jacking actually takes paramount over the effective reduction in center of gravity. Thus you begin to overload the inside front and under load the outside front tire. It is a tricky situation indeed.

Before I review take a second or two to digest the previous paragraph. Put more simply, the wider track width tends to resist lateral weight transfer to a greater degree than a narrower one. Then, due to greater wheel height change a greater amount of weight is put on the inside front tire. These factors may interact with each other differently depending on which end of the spectrum you are on.

How these two factors compliment each other is extremely dynamic. Regarding on track characteristics I boil both of these theories down to two factors. These being tire loading and tire temperature. If you are running in conditions where tire temperatures are on the low side a good strategy for increasing grip may be to generate greater load on just one of the tires. In this scenario you may be looking to get weight on the outside front or the inside front and this may help to generate better tire temperatures and the feeling of increasing front grip. Conversely, if you are understeering on a day where front tire temperatures are normal to hot you may find that attempting to spread load across the two front tires will produce the feel of greater front-end grip. This philosophy however is largely qualitative and before you live or die on these words I suggest you engage in extensive testing.

I contend that both theories regarding front track width hold water, however, it is important to remember the complexity and conditionality of kart tuning. For example, if the track at the moment is yielding high levels of grip. Weight transfer may then occur in greater quantities than opposite track conditions. As a result it may be possible to actually overload the outside front tire and under-load the inside front tire. It may then be true that reducing weight transfer either via front track width or by other means may increase the sensation of front grip.

As always with karting it is important to remember that adjustments are almost always conditional. Moreover, in condition-Z making track width change-B will produce effect-1. Conversely, in condition-Y making track width change-B will produce effect-2. This applies not only to track condition but also what phase of the corner you are attempting to effect. In summary, karts are fickle instruments to tune. Making one chassis change often results in several changes in handling characteristics. Always make sure to evaluate the environment in which you are tuning before making a chassis adjustment. Finally, test chassis adjustments regularly and evaluate the results of the adjustment being sure to consider the condition that any given result was found.

KARTING BRAKES

Fri, 3 Dec 2010 10:15:12 -0500

From the very beginning, karters seemed to focus more of their attention on the go portion rather than on the stopping portion of kart racing. Brakes have seemed to take a back seat to the power plants and chassis in the search for speed. This all started to change as tires became better and offered the karter more grip. Then in the middle to late 1970’s and early 1980’s when European karts manufacturers invaded the domestic racing scene, brakes began to get more attention.

From a historical perspective, karts have evolved from utilizing braking systems that were a simple scrub brake (a metal plate that was pushed into the tire to slow it down or the deluxe versions, used a metal plate with an old tire bolted to the plate so there was a rubber to rubber contact area to generate even more braking friction), to the four wheel hydraulic brake systems we have now. If you have been in karting for any period of time, the brake systems have seen a level of development and improvement over the past 5 years that has out paced the development over the past 35 years. From a braking perspective we are in braking Nirvana.

As the need for better, more performance oriented brakes was more and more apparent, there was a progression from the scrub brakes to the next step which was the Bendix Drum brake. This was a smaller version of the drum brakes that were on the cars back in the day. They were still very large, about the size of the brakes on a VW Beetle, the old beetle. They were simple, heavy, chrome and they worked a ton better than the scrub brake. The brake consisted of a rotating drum attached to the axle and the shoes and backing plate were attached to the frame through some simple bolt on brackets. The two shoes in the brake were forced into the drum via a mechanical linkage. That’s right the brakes were mechanical just like the scrub brakes or brakes on a Model A. The next quantum leap in brakes, were disc brakes. The first disc brakes were a mechanical disc brake. These were manufactured by the Airheart who later became Hurst-Airheart and is now just Airheart again.

These brakes started out life as a part of a large industrial turning machine, we are more accustomed to calling them lathes, but these brakes were originally used to stop lathes. But for a number of years the Hurst Airheart brake was the standard in the industry. They made two different sized calipers a 150 and a 175 (larger of the two sizes). By today’s standards these brakes are not even in the same league. But at the time when Mac’s were the engine of choice they were the standard and they were cutting edge.

The next revolution was the brakes offered by Enginetics, they offered a very simple well made and very robust caliper. The racer could adjust the gap between brake pads and the disc by adding or removing shims that would either move the caliper halves closer together or further apart. This was a quantum leap in adjustability for the karter. Now we could adjust the spacing between the disc and the pads to “tune” the brake for the feel that the driver wanted. This brake was the standard for every American made kart with the exception of Invader who made their own caliper out of bar stock and used modified automotive pads. But the Enginetics master cylinder seemed to be on every kart at the track through the end of the eighties.

This was followed by Martin Custom Products, another American company, started by an ex-employee of Enginetics. Paul Martin decided he could build a better product than his former employer, which he did, and he was off and running. They now seem to dominate the American karting market, especially in the dirt and oval market. With a very well made system that gives the karter a very large series of options, pads, disc types and they have also a front brake system.

The Modern Era
With the advent of the very large penetration of European karts, mainly Italian made karts, the number of brake choices for the karter is even larger. Every brand of kart seems to have their own take on brakes and the parts are not interchangeable from one brand to another so for the kart shop owner this is a positive from a sales perspective, but a negative from an inventory perspective. For the karter, this means that he or she may need to keep more parts in their own selection to support if they have more than one brand of kart they use in their racing arsenal.

The science of brake design and developing brake technology is more about the materials used in the manufacturing of the brake rather than any new or fundamental changes in the mechanics of the brakes. The basic design parameters are pretty much set for the karter. There is the possibility of using a brake pack similar to what is used in large airplanes. Think of a design very similar to a Horstman engine clutch, but instead of being designed to transfer power to accelerate the kart the same type of clutch pack is used to slow the kart. The problem is that the materials required for that type of clutch would be much more expensive than the simple cast iron and composite friction materials and aluminum castings used today. And this type of brake system has some other shortcomings. They require a good bit of maintenance. Where one of the greatest assets that the brakes on karts have is the “almost” maintenance free designs. It is truly amazing the amount of abuse and lack of care brakes on the modern kart have been known to take. Some karters have never been known to never work on their brakes until there a real pressing need, such as they no longer work. It is not uncommon that a kart that is raced 25 to 30 times a year receives very little maintenance to the brake system. This is a true testament to the level of material selection and design work and resulting robustness in the modern karting brake. It may not point to a very good maintenance program, but sometimes the truth is the truth. The fact of the matter is that the kart chassis may be well past its duty cycle long before the brakes wear out or require any replacement of the mechanicals.

There are multiple well known automotive brake manufacturers that have made runs into the karting market. Some of these companies are very well known automotive racing brake manufacturers. Companies such as Brembo, Wilwood, Alcon and Kelgate have all made forays into the karting market. These are companies that are more recognizable or known for high end automotive racing brakes rather than for applications suitable for the kart racing community.

The one common thread between the automotive and motorcycle braking world that is completely transferable to karting is that tires are the weak link in the braking chain. If you are running a hard tire, the brakes will not be able to perform to their maximum performance levels. It is much easier to develop a much greater mechanical load in the brake system than the tires are able to contribute grip. It is very easy to overpower the tires with the brakes. Push the pedal too hard and you will lock up the brakes. There are ways we can control the power to the brakes, the simplest is to not push as hard and use the onboard computer under your helmet and modulate the brakes based on the feedback you get from the pedal and the sensation the kart gives you via the seat when the tires lock up. When the tires lock up the ability to slow the kart in a controlled method go right out the window. By balancing the sizes of the bores in the master cylinder and the slave cylinders in the calipers we can tune the brakes to give us more control. This is usually accomplished by the kart maker, but the option still exists for the karter to look around and play with different master cylinders and calipers to custom tune the brake system to the driver.

The disc is another component you can tune to tailor the brake system to suit your individual needs. Karters have made discs out of everything from Detroit wonder metal, Cast Iron, Steel plate, Aluminum and even exotic metals like Titanium and Beryllium. But the material of choice seems to always gravitate back to Cast Iron. Nothing seems to be able to beat this material for it ability to under go many heat cycles without distorting. It is relatively inexpensive and it has great wear capabilities. Carbon-Carbon was even tried for a short time. It offered great performance and it was incredibly light often the disc would weigh less than the nuts and bolts used to hold the disc to the hub. But it was very expensive; really expensive, a single disc could cost $200.00 to $500.00 dollars depending on the application. The Carbon-Carbon disc also required special Carbon-Carbon brake pads so the cost was really astronomic, but they did work very well in heavy high powered Sprint Karts like shifters, that would really place a real strain on the brakes especially in street races.

But no matter how much things change, they still seem to be the same. Cast Iron is the material of choice and that holds true in 90% of the racing series around the world, not just karts. You will only find the esoteric Carbon-Carbon brakes in the highest formulas racing today like Formula 1.

For the most part, the brakes that were delivered with your kart as new will perform beyond your expectations, last longer, and provide trouble free service over the life of your chassis with a very little care and or maintenance. Today the karter is getting a better more completely designed product than they have in the previous years. It does not matter if you are using a domestic or an imported brake you can expect many seasons of dependable trouble free high performance braking. Keep the fluid clean, the pads in good condition, the hardware secure and in good condition, keep and route the brake lines away from the track surface or any other moving surfaces and the brakes will probably out last the chassis. If you follow those some simple maintenance steps you will most likely never have any real issues with your brakes. Remember take it in deep, trust your brakes and we will see you on the podium.

MAXIMIZING YOUR BRAKES

Fri, 3 Dec 2010 10:10:04 -0500

Often overlooked until an issue arises, your kart’s brakes are a key component that needs attention on a regular basis.

Most karters have left our karts in a cold garage over the winter, ran the same brake fluid for two seasons, or used double the manufacture’s recommended brake pad shims to extend the life of the pads. But to what extent are we jeopardizing safety and losing performance by not paying attention to our brakes? We’ll ask a couple of brake experts and go over rebuilding and maintaining the brake system in the remainder of this article.

Robert Sollenskog, former Toyota Atlantics driver and inventor of the full-contact Thor Brake (see sidebar for this story), describes the fundamentals of what is occurring under braking: “Braking is the simple creation of friction between a brake pad and rotor.”

“For any given semi-metallic brake pad and steel brake rotor to “work” properly, the brake rotor must have friction material transferred to it from the adjacent contacting brake pad. Friction between the two like materials during a brake event has the effect of decelerating the vehicle.”
Click here for more about brakes!
Essentially, kart brakes work the same as any car disc brake or racecar brake. However, there are some differences in pressure ratios, pedal travel, and pad return.

“Brakes are brakes,” declares Paul Martin of MCP Brakes, America’s leading kart brake manufacturer. “Kart brakes are basically the same in design as any other disc brake system, whether it be on your family sedan or your race car. One difference that many kart brake systems have versus auto brakes is the spring return brake pads.”

All shifter karts (and some others) run systems that require dual master cylinders and bias adjusters. These items also need to be inspected for functionality and safe operating on a regular basis.
“Back in the 70’s, the spring return brake pad system became the most common brake because it offered a brake system that didn’t have any brake drag like automotive systems or previous kart brake designs. Larger racecars and your family auto cannot use a system that has mechanical brake retraction because the hydraulic ratios are very different.”

“The master cylinder on your car is nearly the same piston size as our kart brakes but it has to feed four calipers that have very large caliper pistons. This ratio is well in excess of our typical 5:1. If each brake pad pulled back from the rotors .030” of an inch, the brake pedal would have tremendous travel before the brakes would come on. You can see this would never work in the average auto and certainly not a racecar. This does put a little friction in the system but is never noticed because the engines are so powerful. In many karts with only five horsepower engines, this drag can be a big detriment to top end. I call it “free horsepower” because if you don’t take it away with drag, you have it to use to go faster!”

Sollenskog concurs with Martin and continues a step further, “A proper racecar brake has three main characteristics:
1. A stiff pedal that can be used to modulate the brake pressure and thus the stopping force.

2. A short stroke pedal. Perhaps a _” to _” of travel until the brake pads contact the rotor. Traveling at those speeds drivers do not have confidence in their brakes if the pedal needs to travel 2” to slow down. Without confidence they cannot maximize their braking.

3. Brakes are set up to provide good stopping power without losing drivability. By this I mean that the brakes cannot be over sensitive and prone to locking up.

Many kart brakes do not offer any of the characteristics of a formula racecar brake system. The full-contact brakes that we (Elevation Engineering) offer do perform like racecar brakes are meant to: giving the driver a short, stiff pedal allowing he or she to modulate their brake pressure giving them the performance to out brake other karts.”

Common Kart Brake Issues:
But many karters don’t even know the signs a brake problem is about to arise until the brake pedal is pushed to the front bumper with little or no stopping power. However, most brake problems can be prevented with a little preventive maintenance and routine inspections.

“Routine inspection of the brake system should be part of every track day experience, whether racing or just practice,” says Martin. “I start with the obvious mechanical connections starting with the brake pedal and back to the master cylinder. All pivot points should be checked for excessive wear and be sure the safety restraint (cotter pins, quick pins etc.) are in place. I then check the caliper and disc for all physical connections to the frame and axle. Again, looking for loose caliper or disc bolts and being sure the cotter pins are in place.”

Martin continues to explain how this inspection time is also a good time to check for excessive pad wear and leaks, two of any brake system’s most common problems. “This is a good time to look at the brake pads for unusual wear or any cracking or ‘debonding’ of the friction material from the backing plate. Examine all line connections for any signs of leakage. Follow the brake line back to the master cylinder being sure that at no time are the lines able to contact the track or pinch points on the frame. This could cause a catastrophic failure on track. Once back to the master cylinder, again examine the condition of the fittings and be sure all is dry with no sign of leakage. If all of this is in good condition, there is typically no reason to expect any brake problems.”

In addition to routine inspections for leaks, most brake experts will recommend changing the seals in the master cylinder and caliper during the off-season. “I have always recommended that if the kart is used for a full season of racing, the brake system should be part of the winter maintenance schedule,” states Martin. “It would be appropriate to disassemble the system, clean and inspect all the components. I would recommend rebuild kits for both the master cylinder and caliper.

Sollenkog elaborates, “Brake fluid tends to dry the seals out. As a seal begins to dry out it creates more friction in the bore in which it travels. The friction causes the return travel to slow down. A slower brake return can cause momentary reduction in acceleration out of corners. A leaking seal happens at the end of the cycle not the beginning. If you wait until you have a leaking (bad) seal you have already suffered through weeks if not months of ill performance.”

“The second main reason is dirt and dust. Road grime will cause seals to deteriorate much like brake fluid will. At minimum, maintenance between race meetings should involve pulling off dust covers and flushing dirt and dust out with a quality brake clean solvent on both the masters and calipers. A WD-40 chaser is good to maintain lubrication on the piston bore. Replace all dust covers.”

For a heavily glazed rotor, carefully sanding the shiny/glazed look off with a medium grit sandpaper and a sanding wheel can save time.
Occasionally, even with all the preventative maintenance and inspections problems do arise in well prepared racing equipment. One problem that many karters encounter at some point in their racing careers is “glazed brakes.”

Brake “Glazing” and Proper Pad Bedding:
“Glazing of the brake pads is a term used to describe the condition of the friction material when it looks very shiny. This depends largely on the type of friction material. Many years ago, the brake material of choice had asbestos in it,” states Martin. “That type of friction material was very prone to glazing over. When this happened, the brake pads just wouldn’t grip the rotor when the brakes were applied, literally giving the driver the impression he had no brakes at all. As asbestos was phased out and better friction material of carbon metallic compounds became the norm, the glazing problem is not the same.”

Sollenskog continues, “Glazing happens when the friction material on the rotor and pad get overheated. The glazing acts like a surface hardened condensed coating that has reduced coefficient of friction on the contacting surfaces. Brake efficiency is reduced causing brake torque to be reduced as well (ie. The brakes do not slow the vehicle down like they are supposed to).”

“You can see glazing with the eye and feel it with your brake foot. A mild case of glazing can be fixed with sandpaper. By hand sanding or with a small power sander, sand the glazing off the rotor and pads. After re-installing the pad components bleed the brake and bed in the pads and rotor.

For bedding in we suggest:
1. 10 stops from at least 80% full speed using 50% braking.
2. Park and let cool for 5-10 minutes.
3. 10 stops from at least 80% full speed using 75% braking.
4. Repeat step 2
1. You should be ready to use brakes as normal.

If you are an aggressive driver on the brakes or on an aggressive braking track; consider adding a cooling tube to feed air to the brake.”
Paul Martin has never seen the MCP carbon metallic material ‘glaze’ in severe testing, but has had customers over the years tell him they have experienced glazing. “I have always found that when this appears to occur, there were other reasons the brakes were not operating properly. Typically, this has been a poor brake pedal setup that just doesn’t allow the driver to apply the amount of physical force on the system to provide adequate hydraulic pressure to the brake pads.”

“In other words, the driver may be pushing with a tremendous amount of effort, but that doesn’t necessarily relate to system pressure. The entire brake system is nothing more than a means to convert and multiply the drivers pedal effort into the motion that squeezes the brake pads against the brake disc. The multiplication of effort starts with the mechanical advantage of the brake pedal, added to the mechanical advantage of the typical master cylinder, then added to the hydraulic advantage of the master cylinder over the caliper. As an example, the MCP brake system has a normal recommended pedal leverage of 2:1 to 3:1. The master cylinder has a range of 1.5:1 to 2.5:1 ratio. The standard brake system has a 5:1 hydraulic advantage. When multiplied, the system recommendation offers a range of 15:1 to 37.5:1. As you can see, this is a fairly wide range. This allows any driver to find the brake effort and feel he likes the most. The adjustment of these mechanical advantage points is crucial to setting up the brake system.”

“I’m a little off subject, so I’ll get back to the glazing. How to prevent it is to be sure you have the systems setup to provide crisp and relatively easy brake action when the pedal is applied. The previously mentioned adjustments are how to obtain that. Most people would “de-glaze” the brake pads and rotors if they think it has occurred. De-glazing is normally done by removing the pads and sanding them until the “glaze” is removed. Likewise, the rotor can be sanded until it appears dull in appearance. This should offer at least a short-term fix to glazing. I am convinced if the driver would set the system up correctly, this will not happen with today’s brake pads.”

Brake Fluid - There is a difference:
Probably the root cause of the majority of brake problems karters encounter are a result of moisture in the brake fluid (that is assuming the brakes are bled properly and completely of air). Unless you can bleed your system in a moisture free clean room, as soon as the bottle of brake fluid is opened moisture absorption begins.

“Like all fluids in a high performance vehicle, brake fluid should be changed at the start of a new season and every couple of races. Brake fluid begins to deteriorate as soon as the seal is broken on the bottle exposing it to the moisture in the air. All those open bottles that you have in your garage that are older than 2 months or have been sitting without the top securely fastened: throw them out!” decrees Sollenskog.

“Changing of fluid color is never an accurate indicator of fluid freshness. Brake fluid “goes bad” when it absorbs even the smallest percentage of water. The vast majority of brake problems can be directly attributed to “bad” brake fluid. Change your brake fluid in regular intervals and when in doubt.”

Sollenskog continues, “The minimum brake fluid that should be used is DOT 5. All the DOTs are glycol-ether based except for DOT 5.1, which is silicon based. Dot 5.1 is problematic in high performance applications. Silicon has a much higher rate of expansion than the glycol-ether based fluids. Unless you are willing to run a wider brake pad air gap to compensate for the loss of gap due to DOT 5.1 expansion, stay away. Remember the larger the air gap the longer the pedal travel!

Since our full-contact brakes are designed with minimal pedal travel we found out in testing DOT 3, 4, and 5.1 wouldn’t work for us. After initial fluid problems and an extensive fluid study we chose to use synthetic NEO 610 with our brakes. The right fluid is worth it and that is why we supply a bottle of NEO 610 with all our brakes. The 600 series is above DOT-5 and removes all doubt.”

Paul Martin agrees, but offers a counterpoint concerning the advantages of using DOT-5 silicone based brake fluid: “Most American built karts using the MCP/Enginetics systems use DOT-5 silicone brake fluid. This fluid is non-hygroscopic, meaning it does not collect moisture. In its original form, the fluid is clear but a purple dye is added to give it color. If using nylon brake line, the sun’s rays will bleach this color out and the fluid returns to near clear. This has no effect at all on the properties of silicone brake fluid.”

“Standard DOT-3 and DOT-4 fluid are extremely hygroscopic,” continues Martin. “They are very prone to absorbing moisture, especially in a humid environment. When subjected to moisture, these brake fluids absorb this moisture and the consequence is a lowering of the boiling point of the fluid. This is why most racing brake systems suggest changing the brake fluid every race day. DOT-5.1 fluid is a synthetic fluid with properties more in line with glycol based DOT-3 and DOT-4 fluids. It has a high boiling point but not as high as silicone fluid. Every brake fluid has it good points and bad. Go with the brake fluid recommendation and you should be fine.”

Maintaining the Pad and Rotor Air-gap:
Along with faulty, or the wrong brake fluid, the air gap between the pad and rotor are another point of contention for karters to concern themselves with. For obvious reasons, karters don’t want the pads and rotor to make contact when they’re not applying the brakes (for example, while under load exiting a corner). This will rob the kart of horsepower as easily as choking the motor. However, there is a trade off; too much air gap will give an extra long pedal throw which isn’t optimal for performance.
“Air gap for the pads to rotor clearance is another of the many adjustments available to the user. If the driver likes a long brake pedal stroke, then he/she will use a fairly large pad gap,” explains Martin. “Obviously, the opposite is in effect if the driver likes a short pedal stroke. If you start out a race with a short stroke and the stroke increases noticeably during the race, your pad gap will be much larger and need attention. The only reason a “too big” air gap might cause the brakes to lock more easily will happen more because the pedal ratio will change as the stroke gets longer.”

Sollenskog elaborates on the changing pedal ratio: “Many karts have different linkage pick up points on the brake pedal and master cylinder to change the kinematics. In effect by changing the mechanical advantage in the linkages you can increase the volume of fluid relative to the pedal travel. Keep in mind however that when this is done, the effective line pressure to the brake pads is reduced. This creates less brake force. It is a tough balancing act and most racers just deal with a long pedal.”
“Brake rub as many racers have experienced happens in corners as the chassis flexes allowing the inside rear wheel to lift off the ground. As a rule of thumb the longer in overall length the brake pad is, the more air gap is needed to compensate for brake rub. The increased air gap leads to an increase in pedal travel to achieve a braking event.”

One rather new (at least to karting) concept to eliminate brake rub is the concept of the floating rotor. Used in formula cars for years, many of the top European manufacturers at least offer a rotor system with some degree of free-float. Some of the new full-contact systems, such as the Thor Brake, have over six degrees of free float, which according to the manufacturer allows for a rear wheel to be up to 3” off the ground under chassis load without any rubbing.

Karters do have a few options in reducing (or managing) air-gap. Most karting systems require a thin aluminum shim to reduce the air-gap. Some manufacturer’s systems, such as CRG, are self-adjusting via a free-floating pad that knocks back the caliper piston when the rotor flexes against it. MCP has a simple system that allows for adjusting the air-gap with an Allen wrench while in the pit/garage.

“The shims are generally thin sheets of aluminum that do not hold their flatness. These stacked together will act like a spring giving the driver a spongy feeling at the pedal,” states Solleskog.

Martin explains the use of shims in a bit more detail, “There are two ways to use shims. The American systems of the past used shims between the caliper halves to adjust pad gap. There was no reasonable limit to how many shims could be used in this manner. The European style of using shims puts the shims directly behind the pad between the brake pad and the caliper piston. There will be a limit to how many shims can be used in this manner because as shims are added, the amount of stroke is being limited. It would be possible to add so many shims that the return springs reach a coil bind state. As shims are added, the feel of the brake is effected somewhat because the return springs are being compressed more every time another shim is added. Although the springs don’t have a lot to do with pedal effort, you can feel how much is required just to push the springs as this is the pressure required up to the point the pads make rotor contact. This effort will increase as the springs are forced to start from a more compressed position.”

Rebuilding the Master Cylinder & Caliper:
As Paul Martin suggested earlier in this story, it is a good idea to rebuild your caliper and master cylinder annually. Brake fluid is a very harsh chemical and dries seals out, especially when left sitting for a prolonged period of time causing leakage and a loss of pressure. In the following paragraphs and photos, we’ll examine the disassembly and replacement of the brake seals.

Step one is to break the line and drain the old brake fluid –trying to keep it off the kart’s paint. Remove the brake line from each mounting point on the master cylinder and caliper, and blow out an excess fluid with a compressed air nozzle. The next, and obvious step, is to remove both the master cylinder and caliper from the kart.

For this example, we’ll assume the caliper is of the traditional type (this excludes the Birel “banana” caliper, which uses an external piston design). Assure that all the fluid is drained before; this might require not only remove the lines but venting the system by removing the bleeder screws. Next, remove the brake pads. As mentioned earlier, most kart calipers use a system of retainer bolts and return springs to; these will need to be removed for the pads to be removed and eventually the caliper pistons.

With the pads and brake fluid removed, it’s time to remove the caliper pistons. Over the years, many karters have tried twisting, pulling, and prying the pistons out. This is 100% the wrong thing to do! It is essential not to scratch the piston or cylinder wall; this could cause a leakage of fluid or failure to build enough pressure to stop the kart at all.

To properly remove the caliper pistons, the first step is to seal off the bleeder screws and all but one of the brake line fittings. If the caliper has two brake line fittings, it is likely they operate independently and you will not need to seal off the opposite one. Using a very low air pressure and increasing it slowly, place a rubber tipped air-nozzle in one of the brake line fittings and “blow” (slowly!) the piston out. You may even use a small piece of wood where the brake rotor would be to stop the piston if it shoots out quickly.

Behind the pistons or on them (o-ring) is the piston seal. Typically, anytime the caliper pistons are removed, the seals are replaced. Also, take a look at the caliper cylinder walls for scratches to assure no debris got by the piston and seals.

At this point, the pistons need to be inspected for brake dust and other buildup that has not allowed them to return fully into the cylinder. Often there is some residue from brake pads, grease, and “track dirt” that build up around the outer edge of the piston. To remove any buildup, wipe off with a brake parts cleaner soaked shop rag.

Clean all pieces thoroughly with brake parts cleaner, and begin to reassemble with new seals. When installing the new seals and pistons, lightly coat both with the manufacturer’s recommended brake fluid. This will help ease reassembly and assure a better seal.

At this point, it’s time to move to the master cylinder. Most kart master cylinders are very simple, and not that dissimilar to any other racecar’s master cylinder –with the exception of the volume of brake fluid. The lever that joins to the brake rod, and eventually the pedal, pushes a piston –which is usually backed by spring.

The master cylinder piston is usually held in by a snap-ring. By removing this snap-ring, the piston, seal, and spring can be removed. Both the seal and spring should be replaced (springs can become compressed and reduce pedal pressure). Clean out the master cylinder and assure no debris scratched the cylinder walls. Reassemble as it came apart with similar procedures used on the rear caliper. Most master cylinders have a dust shields at the lever to keep dust out of the piston area; assure these shields are in place and free of tears.

In this example, the piston & dust ring ride in front of the seal. As pressure forces fluid against the seal, it pushes the piston out. The piston is returned when the spring pressure from the pad retainer springs/bolts exceeds that of the hydraulic pressure coming from the opposite direction.
Reinstall the calipers, master cylinder, and brake lines. Finally, you will need to bleed the brakes using the manufacturer’s recommended fluid. What’s proven best to bleed kart brakes time and time again is a gravity fed bleeder that screws into the master cylinder. This style bleeder essentially pushes the air out the bleed screws, almost doing the work for you. Be sure all air bubbles/pockets are out and test the brakes before hitting the track full throttle!

Conclusion:
With the exception of full-contact brakes such as Sollenkog’s Thor Brake line, the future of karting brakes appears to have reached an evolutionary period. Carbon fiber pads and rotors made a brief appearance around the turn of the millennium; however, cost issues legislated them out.

“Carbon/carbon systems normally require a fair amount of heat to work properly. This is hard to achieve in the short time karters go out for qualifying sessions or the first few corners of a race. Most carbon metallic systems work instantly regardless of temperature and therefore have prevailed. I don’t think exotic materials have a place in karting in my opinion. This doesn’t mean they won’t appear,” explains Martin. This being said, some karts are arriving from Italy with optional ceramic-based rotors.

Your kart’s brake system is as important a part of the overall performance as it is a safety item. Today’s kart brakes come in a variety of shapes, sizes, and pad compounds giving drivers the opportunity to tune their brakes to their personal preference. But no matter what combination is best for your personal driving style, it is well advised to follow the manufacturer’s recommended maintenance schedule and use only their recommended fluid to assure safe and consistent performance.

NKN would like to thank Paul Martin of MCP Brakes in Dayton, Ohio (www.mcpbrakes.com phone: 937-228-0370) and Robert Sollenkog of Elevation Engineering (www.thorbrake.com phone: 317-459-4010) for their contributions to this article.

INSTALLING A SEAT

Fri, 3 Dec 2010 10:06:55 -0500

So you have that new chassis and you now need to mount the seat. Mounting a seat can be a painful experience, and if not done correctly, can lead to problems on the track. I have mounted a number of seats over the 10 years I have been in karting and I have developed a simple step by step process that includes some hints to help prevent issues down the road.

Watch the Seat Mounting Video!

First of all, you have to make sure that you have a seat that fits you properly. The best way to choose a seat is to actually sit in one before you buy it. Fiberglass seats are made in high production volumes and the tolerance in sizes can be larger than you think. Go to your local kart shop find a seat you like, put it on a carpeted floor and try it on. The seat should be snug but not tight. Your upper torso should also fit deep enough into the seat that your sides are supported and not on a pressure point that could cause rib soreness or even injury. As you sit in the seat on the kart shop floor, you need to keep in mind that the seat will flex less after it is mounted to your chassis so if it is a little tight now it will be too tight after mounted up.

After you have made your seat selection you will need some seat mounting hardware. Many of the bigger name seat manufacturers sell seat mounting hardware in a kit with everything you need. If you choose not to go that route you will need some basic hardware.

HARDWARE
4 – Flat head Allen cap bolt (usually 8 X 25 mm) for the upper seat mounts and seat struts
2 – Flat head Allen cap bolt (usually 8 X 80 mm) for the lower seat mounts
6 – Conical washers to fit the bolts you’re are using (I recommend plastic)
6 – Large fender washers
6 – Large rubber washers at least as big as the fender washers
6 – Regular washers to fit the bolts
6 – Nylon lock nuts

I recommend the plastic conical washers because the surface of the fiberglass seat is not at all flat. Using an aluminum conical washer will eventually dig into the fiberglass and with the vibration from the engine, will crack or wear through the seat itself. I also use the rubber washers and fender washers for the same reason. Use the rubber washer between the fender washer and the seat to keep the fender washer from digging in. Use the fender washer to provide enough mounting surface for the seat struts and seat mounts to disperse the load over a large enough area of the seat.
As for what tools you will need, I recommend using some sort of seat mounting jig that holds the seat at the correct height from the frame rails. I use a nice seat jig specially made for this, but you could use a piece of wood taped securely to the bottom of the frame rails. Since most seat bottoms are flat these days, you can take advantage of it. That flat surface makes it easy to set the seat in place. I also use another small jig to hold the seat back relative to the rear axle. Again, if you don’t have the jig, you can make something out of wood. These jigs, while not required, will make the seat mounting job much easier to do. Other tools you will need:

TOOLS
Large rubber mallet
Electric Drill with proper drill bits
Measuring tape (I prefer metric, fractions are too hard on my brain)
Permanent marker
Wrenches

Ok now you have your seat, your tools and hardware. You are ready to go right? Wrong. You need to get with your chassis manufacturer and have them tell you the recommended seat mounting locations for your chassis. This may sound unnecessary, but when your chassis was developed one of the things that was tested and dialed in was the seat location. Having the seat in the proper location will not only help the chassis behave like it was designed to, but will also ergonomically fit you better. All of the major chassis manufacturers have this information available. Just give them a call. If your manufacturer doesn’t have it or if you have an old chassis that is no longer supported, follow these simply rules of thumb:

1. Set the bottom of the seat even or just slightly higher than the bottom of the frame rails. This will keep the seat from bottoming out on the track when you go off.
2. The center of the seat will most likely need to be slightly offset to the left relative to the steering wheel. This is to make room for the engine on the right side and help balance out the corner weights on the scales.
3. Set the chassis on the ground and put the seat approximately where it will mount and sit in it. Grab the steering wheel and tilt the seat fore and aft until you find something that feels comfortable. Have someone measure that location relative to the rear axle and the steering upright. This will be a decent starting point.

Now that you know where to mount your seat, you will need to start to fit the seat in place. This is a somewhat tedious process but if you take your time and do it right the rest of the process will go much easier. Attach the seat jig or piece of wood to the bottom of the frame rails. This will define the height of the seat relative to the frame rails. To adjust, I simply tape a small block of wood to the flat portion of the bottom of the seat. This will also help to define the seat back angle as well.

Use a rubber mallet or dead-blow hammer to bend the seat attachments in or out as needed.
You will need to bend the welded upper seat attachments in or out to accommodate your sized seat. As a rule of thumb only bend the left side one. The one on the right is set to make room for the engine. Moving that one outboard will cause clearance issues when you put the engine on. To bend the seat attachment simply hit it with a large rubber mallet or dead blow hammer. Be mindful not to bend these large amounts or bend then in and out multiple times as that can cause cracks in the steel. Continue to adjust the attachments until the seat sets on the seat jig and snuggly between the seat attachments.

With the seat sitting on the lower frame jig and the attachments snuggly holding the sides of the seat, you can begin to set the exact location of the seat in the kart. Most manufactures will give you measurements from the front kingpin to the rear centerline of the seat as well as the distance from the rear axle to the lip of the seat back. Moving your seat around, resetting the attachments as needed measure and re-measure until your seat is right where it is supposed to be. Carefully look at the overall location of the seat and make sure it makes sense. Is the bottom of the seat too high or too low? Does it look offset too much relative to the steering wheel? Is it rotated in place relative to the steering wheel? Again take your time and do it right.
How to Repair a Kart Seat
With the seat now set and in the recommended location, mark where the holes need to be for the upper seat locations. Do not drill yet! Now you need to do some fine tuning to make sure the seat sits in place without binding or having unnecessary pressure points that can eventually crack the fiberglass. To do this notice the mounting tab orientation relative to the seat itself. You need to make sure the tab sits as flush as possible to the seat. Adjusting this is a matter of using an adjustable wrench and twisting or bending the tab to make it mate flush with the seat. This again will take some trial and error but if done correctly you won’t be driving with a cracked or broken seat halfway through the season. Now with the tabs properly adjusted it is time to drill the holes for the upper attachments. Make sure the marks are still correct after you adjusted the tabs. If they are, simply drill the holes in the locations you have already marked. If not, remark and re-measure to be sure. Remember measure twice, drill once.

OK, with those two holes drilled you can put in some bolts. Using the shorter of your mounting bolts slide the bolt through the plastic conical washer and then through the seat. Put the rubber washer and fender washer between the seat attachment and the seat. Make sure to put the rubber washer between the seat and the washer. This will keep the fender washer from digging into the fiberglass. Repeat this for the opposite side. Use a small washer between the nylon locknut and the seat attachment and tighten until just barely snug. You will still need to move the seat around slightly for future steps.

Now for the easy part, with the seat supported by the two side bolts, and still being held up by the lower seat jig it is time to work on the lower seat attachment points. These are small tabs welded to the frame right behind the steering upright. Like before you will need to use the adjustable wrench to bend or rotate the tab to be parallel to the seat surface. This will provide a more stable and secure platform to support the seat. You will likely need to come up with some kind of spacer between the tab and the seat to make up the difference in height. The most common practice here is to use a bunch of large washers or aluminum spacers. I use simple grey 1/2in PVC plumbing pipe cut to length. It’s lightweight, inexpensive and easy to work with.

If you are using a clear fiberglass seat, marking the holes for the lower attachments is simple. I put a pencil through the attachment point until it touches the bottom of the seat. Make sure the angle of the pencil is perpendicular to the tab and seat. Now since the seat is somewhat transparent you will be able to see the erasure end of the pencil though the seat to mark the hole. Now simply drill the hole from the seat side. If you are using a black or opaque seat you will need to mark the holes from the bottom side and take the seat out to drill the holes.

Use the same hardware attachment technique as with the upper attachment. Make sure to put the rubber washer between the seat and the fender washer. Then put the spacer in place. Tighten all of the seat bolts down and you are basically done. Don’t over tighten the bolts to the point you hear cracking. Fiberglass, no matter how strong, can’t match the strength of the steel bolts. If you hear too much creaking, you might need to look at the orientation of the tabs relative to the seat again. They need to be parallel and mate at closely as possible to the seat.

Now with the seat bolted in place, it is time to consider seat struts. Seat struts are a tuning tool than are standard equipment on 99% of all karts. They are simple semi round tubes that attach to the seat and the axle bearing cassettes. These provide additional stiffness to the upper seat structure and add stiffness to the rear of the kart. Again contact your chassis manufacturer about how many seat struts to use and where to attach them. Use the same techniques as the seat attachments to put the seat struts on as well. If your axle cassettes are threaded. be sure to use a thread locking compound to keep that bolt from loosening out on the track.

So that is the simple step by step process to mount a seat. Remember to use rubber washers between the seat and the washers, bend the tabs so they mate with the surface of the seat and always measure twice and drill once. Using these techniques and taking the time to do it right will help make sure you have a successful karting season.

REPAIRING A SEAT

Fri, 3 Dec 2010 09:47:01 -0500

Kart seats are the one of most abused parts on a kart.
First, it gets numerous holes drilled in it to locate it in the chassis and find that “sweet spot” to make your kart handle like it was intended. Then more holes are added to find the proper rain setup and yet another to let water drain out when it finally does rain. Let’s drill some more holes to mount lead ballast, and maybe a few more to mount some of the all important accessories for our shifter karts. Next we’ll drive straight over that 4” tall curb during a qualifier lap or maybe by “oops” during a race. By mid season, your new seat is looking pretty hammered and the scrapes on the bottom of the seat are deep enough to see the track surface below.

Fiberglass repair…yuck. It’s nasty, it smells bad, and well, when done wrong can make your expensive seat look like your hippy neighbor’s home-built camper shell. Fear not. Fiberglass repair doesn’t have to be a nasty job, you just need a little instruction and some quality materials. Here’s a step by step approach to help you do a quality repair job with a lot less mess or hassle than you anticipated. Along the way we’ll learn just enough about composites to make you ready to tackle your repair job with confidence.

You will need:
• Latex or vinyl gloves
• Dust mask or respirator
• 36 and 80 grit sandpaper
• Sanding block or a piece of nice flat wood
• Disposable plastic cups
• Stir sticks
• Small disposable brush
• A plastic squeegee (cut up pieces of a milk jug will work in a pinch)
• Sharp scissors
• Masking tape, 2” width
• Lacquer thinner
• Woven fiberglass cloth.
• Polyester or epoxy based resin and hardener.

Get organized
Make yourself a clean, clutter-free workspace. Do not begin this task with your engine disassembled on the workbench nearby. Fiberglass dust will find its way into everything close by, so take a few minutes to put away critical tools, instruments and equipment. Lay out some newspaper on a clean workbench surface. Tape the paper to the bench and organize your supplies.

Assess the damage
Clean the seat with some lacquer thinner to remove any grease, rubber marks, etc from the damaged area. Tape off an area a few inches larger than the damaged area with masking tape. Begin sanding the damaged area with 36 grit sandpaper, removing any splinters completely. A die grinder with a sanding pad works great for this but a little elbow grease and some patience works just as well. Don’t be concerned if you sand all the way through the seat, it’s more important to remove all of the damaged material.

With the damaged area fully exposed and the surrounding 2-3 inches scuffed properly with 36 grit sandpaper, its time for another round of cleaning. Wipe the area thoroughly with a clean rag and some lacquer thinner. If you’ve cut all the way through the seat during the damage removal process, flip the seat over so the inside is facing you and place a few layers of some two-inch wide masking tape over the hole. Masking tape does a remarkable job of acting at a temporary barrier that resin will not stick to when cured. The tape will more or less take the shape of the seat and will act as a temporary mold to support the repair job.

Select proper materials
Here’s where most folks go wrong with their repair job. They purchase their fiberglass cloth at the home improvement store simply because it’s convenient. Convenient, yes, if you were fixing Aunt Thelma’s bathtub on a Sunday evening. But that’s not what we’re doing here. We’re fixing a racing vehicle, so the repair needs to be strong and lightweight. Do yourself a big favor and purchase the right stuff for the job. Among the most important choices is the type and pattern of fabric. We won’t get into engineering mechanics, but here’s basically what you need to understand about composites. Fibers need to be placed in the same direction as the load that is being placed upon it. Think about gluing 5 Popsicle sticks together side by side to make a flat assembly. Breaking the assembly apart is very easy along an axis perpendicular to the stick’s glued edges. That’s because we’re only relying on the strength of the glue to keep the assembly from breaking. Now consider breaking the assembly along an axis parallel to the stick’s edges. It’s considerably more difficult (See illustration, page 55). Imagine you were building an airplane wing from Popsicle sticks. Which direction would you orient the sticks?

Now that we understand the importance of aligning our material with how it will be loaded, it should be pretty obvious that you want to avoid the chopped strand matted material. This material is easily identified by the tows of fabric going in every direction with no apparent care for uniformity. True, these types are less expensive than a woven cloth, but they also do not offer the same strength to weight ratio as a woven cloth. To make up for its haphazard construction, the chopped strand mat fabric must be considerably thicker, and therefore heavier to obtain the same strength as a proper woven cloth. Save the chopped strand mat for Aunt Thelma’s bathtub.

Instead, purchase a woven cloth worthy racecar or airplane construction. Contrary to what you might think, you won’t have to spend a fortune either. You should be able to purchase enough cloth to do several repair jobs for less than $15. Aerospace grade fabrics come in a myriad of patterns, but for our project a plain weave will work just fine. Plain weaves are just what they sound like, one tow of vertical fabric weaves above and below each passing horizontal tow in a 90 degree pattern. These types are used most frequently for relatively simple shapes or flat panels and they are a great choice for the bottom of our seat because it will support the load (of your body) uniformly. Other weaves include twill, crowfoot, satin, and leno, wherein the patterns that skip over and under corresponding tows in a repetitive fashion. These can be more flexible than plain weaves and are good for complex contours and tight radius parts.

Aircraft Spruce and Specialty Co. supplies have a nice selection of aerospace quality materials at a competitive price - even in small quantities. Good deals can also be found on the web, but beware that many web-based suppliers who offer seemingly good prices per square yard will make you pay a premium for their “cutting” or shipping charges. Though there are many good choices available from Aircraft Spruce, the Rutan bi-directional fiberglass cloth is a great choice for its price, strength to weight ratio, and easy of workability. It will also lay down nicely into a pretty tight radius when laid up at 45 degrees to the woven pattern, so it can be very versatile when required.

Prepare your materials
Cut up some fiberglass strips in varying sizes to fill in the void. The key to a sound repair is to start with small strips barely big enough to fill the cavity and gradually increase the size of the strips until you have the void completely covered with maybe an inch or two larger than the damaged area. Starting with small strips allows the glass to lie down nicely into the void, reducing the chances for air entrapment during the lay-up. Air entrapment is the biggest enemy in composite construction, so take your time to make strips that fit nicely into the void and place them in order on your workbench from smallest to largest.

Now that you have your fiberglass strips neatly arranged, let’s go over the basics of the resin system. Resins are typically comprised of two separate parts, the liquid resin and a catalyst (hardener) that are mixed together in proper ratios to form a solid. In composite construction, the resin is merely the bonding agent that does little more than hold the fiberglass cloth in its proper orientation. Resins have very little strength compared to the fiberglass cloth, (Popsicle sticks example, below) so don’t get fooled into thinking more resin will make a stronger part. Excess resin only adds weight to the part and can make a real mess.
How to Install a Kart Seat
When selecting a resin system, consider the environment it will be used in, temperature and humidity, time it takes to cure, mixing requirements, and cost. There are many resin systems available. Most of us are familiar with the polyester based systems. These are the inexpensive types found at hardware stores and produce the familiar odor that we associate with boat repair shops. Polyester systems are pretty thick (viscous), and don’t “wet out” the cloth as easy as some of the epoxy based systems, so you end up with a heavier repair job. They can also cure very quickly – sometimes in a matter of minutes making them a good choice for performing emergency trackside repairs. Epoxy systems produce stronger bonds than polyesters, and are designed for higher performance applications. We selected the West Marine epoxy resin #105 and #206 hardener for our project because it’s a high quality system that is aerospace proven and easy to use for even a novice. The West System utilizes a mini pump kit that precisely meters the proper ratio of resin and catalyst without the need for expensive scales. Epoxies are much more sensitive to proper ratios than polyester resins so follow the manufacturers’ mixing instructions carefully.

Regardless of the type of resin you use, keep in mind that once the resin and catalyst agent are mixed, the mixture has a specified amount of “open time” before it begins to cure. Ambient temperature can change the amount of open time so be sure to follow the manufacturers instructions carefully. Once you’ve mixed your resin, the clock starts ticking, so it’s important to have all your tools and materials ready and organized ahead of time.

Do the lay-up
Having followed these easy steps, you are now ready to start the lay-up. Disposable, lightweight, latex or vinyl gloves are an absolute necessity from this point on. Meter out the proper ratios of your resin system in a plastic cup and mix thoroughly with a wooden stir stick according to the manufacturer’s instructions. Avoid stirring too quickly so as to “whip” air bubbles into the mixture; we’re not making an omelet here. Stir the mixture uniformly while occasionally scraping any resin off the sides of the cup. Also, it’s always preferable to mix up small amounts or resin at a time and make new batches as needed. Mixing up one large batch of resin that fills up the cup full will often cause an “exotherm,” a chemical reaction that generates excessive heat and causes rapid, premature curing of the resin system. Exotherms can ruin your lay-up, and can even be a fire hazard in extreme cases. For small projects like this, a good rule of thumb is to only mix up batches that are about 1/3 the cup’s capacity.

Using a small brush, apply enough resin into the cavity of the seat to lightly cover the repair area. Begin laying your fiberglass strips into the cavity, starting with the smallest piece. Press the glass into the cavity with a series of light dabs from the brush. This technique is called “stippling” and is intended to push the glass into the void while forcing out any trapped air. Make sure the glass is uniformly covered with resin and that there are no white areas visible in the glass. The glass should be completely translucent when properly wetted out. Continue adding the layers of glass using the stippling effect on each layer. As you work your way out with larger pieces of glass, you can begin using the squeegee to draw out excess resin from the lay-up while forcing the glass down against the seat and further removing any trapped air. Continue using the squeegee until you can no longer see any “waves” of resin being pulled out in front of the squeegee.

Examine the repaired area for any remaining air bubbles or for any areas of the glass that still appear white, indicating dry areas that will have to have some additional resin added by stippling action. Allow the lay-up to fully cure according to the resin manufacturer’s instructions. Avoid the temptation to poke at the lay-up. Be patient. If you want to get an idea of the curing progress, check the leftover resin inside the mixing cup.

Finish the repair
After the lay-up has fully cured, remove the masking tape and use your sanding block to smooth the repaired area. There will likely be some very sharp daggers of fiberglass out at the edges of the repair, so be careful handling the seat until you have the area sanded smooth. Be certain to use a dust mask or respirator while sanding. The sanded particles are very fine and can become airborne while sanding, causing you to inhale them. Keep in mind that the seemingly harmless fine particles are actually tiny shards of glass and resin. Start sanding the area with course sandpaper to remove excess material quickly and work up to some finer sandpaper to provide a nice smooth surface. Once sanded smooth to your satisfaction, wash the seat with warm soapy water to remove any leftover sanding dust. Finish the repair by applying a protective clear coat such as spray painted lacquer, or enamel based clear. Clear coating the part will restore the discolored repaired area to its original glossy finish to match the rest of the seat.

Fiberglass repair doesn’t have to be a real mess, take your time, use proper materials and methods and you can take satisfaction in keeping your seat looking and performing like new.

Sources:
Aircraft Spruce and Specialty, (877) 4-SPRUCE, www.aircraftspruce.com
Rutan bi-directional fiberglass fabric, West Marine, (800) 685-4838, www.westmarine.com