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International Karting Industry Buyer's Guide

GO KARTING!
A Guide To The World's Most Popular Motorsport.

Kart Expo International

ATTAINING MAXIMUM PERFORMANCE FROM A CENTRIFUGAL CLUTCH ON A FUN KART
By James F. Donovan

Just what is a centrifugal clutch? A clutch is an automatic transmission which is attached to the crankshaft of an engine that activated by the increased RPM of that engine. 

Under correct conditions, a clutch should not engage when the engine is at idle speed. Each engine manufacturer sets the idle speed of an engine at the factory. The idle speed of an typical 4-cycle engine is normally around 1,650 RPM +/- 200 RPM. 

However, there are several things that can cause a clutch to engage at idle. Because the fun kart manufacturer does not start each engine after the kart is assembled, it is important for the dealer or kart owner to take a couple minutes to read the owners manual and review the recommended procedure when starting or servicing a new kart. 

Throttle linkages can bend while riding or in transit to the dealer. It is highly recommended to always start a go-kart with the rider sitting in the drivers set with his/her foot on the brake pedal - you know, the one on the left! 

An important reminder: pedals on go karts are in the same position as in an automobile:  the throttle pedal (GO) is on the right, the brake pedal (STOP) is on the left. 

If a driver must start his/her own kart, then place the front end of the kart against a stationary object like a tree or fence post. Once in the kart, you can roll it backwards to get into the kart and in a position to drive it. 

During assembly at a kart factory, it is possible that too much tension was placed on the throttle linkage causing the engine to idle above 2,000 PRM which is the engagement speed for 4-cycle centrifugal clutches. In other words, the kart will begin to move without your foot on the throttle pedal.

Think and stress safety!

When you start the go-kart, be in a position to quickly shut off the engine, if the clutch begins to engage, i.e., the kart starts to move by itself.  Most karts have two shut-off switches (typically called “kill switches”). One is on the steering column near the steering wheel and the other in on the engine itself.  If the clutch wants to engage itself, turn off the engine and try to verify what is causing the problem - stuck throttle linkage, bent throttle rod - any number of reasons. If you can’t determine the problem, bring the kart back to the dealer where it was purchased or to a good lawnmower shop. The mechanic should be able to use a tachometer on the engine to verify what is causing the problem and adjust the idle speed to the proper setting.  Note: You cannot verify the idle speed by listening to the engine and concluding it is too high or too low.

Some driving habits that can ruin a clutch are:

DRIVING TOO SLOWLY

A clutch starts to engage around 2,000 RPM and will lockup around 2,600 RPM. Driving at full throttle gives the clutch a chance to cool down. Full throttle locks the shoes in the clutch against the drum. When the clutch is not “locked up”, the shoes slip against the drum causing tremendous heat which does a number of disastrous things. 

First, The tremendous heat generated will dry up the lubrication in the oil impregnated bushing which will quickly lessen its life and secondly, the heat will anneal the spring which is the heart of the clutch. If the shoes turn blue or purple from excessive heat more likely the clutch is ruined and the spring is no longer capable of pulling back the shoe at idle speed.  The longer you drive a full throttle, the better off it is for the clutch because it gives it a chance to cool off before the next engagement.

DRIVING WITH YOUR FOOT ON THE BRAKE

This is a common problem with new drivers who are unsure of themselves. When riding a go kart for the first time, try to find a open area that has no obstacles that you have to maneuver around until you get used to the brake (remember, the pedal on the left) and throttle (the pedal on the right). The driver must first be able to build up his/her confidence on the kart before obstacles are in their path. A small back yard is not a good place to learn to drive a go-kart. In my opinion, a minimum of ¾ of an acre is the size area to learn to drive a go-kart.  Teach your child to drive with one foot on a pedal at a time - be it the brake or the gas, but do not press on both pedals at the same time. You either want to go or stop but you should not do both at the same time.

CHANGING THE SIZE OF YOUR TIRES

Putting on tires that are larger diameter than came with your kart will also result in clutch problems. Tires exceeding 13” in diameter stress out a clutch if the kart is not properly geared for the larger tires. If you are driving on smooth flat terrain then you may be able to by with 14” tires, but once you get on hilly terrain, deep grass, then you are again putting additional strain on the clutch, which will cause premature wear. Big tires look neat on a go-kart but you create new problems changing to a bigger tire when the clutch isn’t designed to handle them.

WEIGHT

A centrifugal clutch is designed to be able to move a certain amount of weight, Once the weight limit is exceeded, then the life of the clutch will be shortened. A good rule of thumb is the kart and the driver (and passenger when it is a two seat kart) should not exceed 400 pounds.  The kart weighs around 150 pounds, add to this a driver (and passenger weight, again if the kart is designed for two people). If you know ahead of time that you will exceed the 400 pound weight limit, then I would suggest purchasing a kart equipped with a torque converter. This will avoid any problems with burning up a centrifugal clutch by asking it to do more that is was designed to do. 

GEAR RATIO

The sprocket on the engine clutch  and the one on the rear axle should have a ratio close to 1:6. This means for every tooth on the clutch drum, there should be 6 teeth on the rear sprocket. (Examples: 10 tooth clutch sprocket/60 tooth rear sprocket or 12 tooth clutch sprocket/72 tooth rear sprocket). 

A torque converter has a variable speed system between the driver and the driven pulleys so it can improve upon this ratio, which gives the torque converter an advantage over a straight clutch system. It improves the ratio by approximately 3:1 and can turn larger tires and drive at slower speeds without doing any damage to the clutch system. A torque converter is a more expensive system initially, but it will last longer and is more trouble free when maintained properly.

RESTRICTIONS

Don’t try to reduce a go-kart speed by limiting the travel of the gas pedal or by putting a restrictor plate in the carburetor to limit full RPM. Either of these methods will result in the clutch slipping, which is self-destructive. A clutch needs full RPM to lock up as quickly as possible to be able to start to cool down. To slow down a go-kart you would need to purchase a gear reduction unit, which is like “training wheels” for a go kart. It will enable the driver to get used to how a go-kart handles at slower than normal speeds.  A gear reduction unit can reduce the speed of the go-kart about 50%.

PROLONGING THE LIFE OF A CENTRIFUGAL CLUTCH

Now that you understand some of the “don’ts of owning a go-kart, what must you do to prolong the life of your centrifugal clutch? Do some preventative maintenance, so the kart can be driven rather than be in the repair shop all the time. How? Oil the busing that is located inside the sprocket at least after every 2 hours of driving time. Where do you oil it? Right where you see the snap ring on the sprocket at the end of the clutch. 

CLUTCH LUBRICATION

There is a bronze bushing behind the snap ring that needs lubrication. With the engine off, squirt several drops of oil while the bushing is warm. At the same time, oil the chain. What oil should be used?  Any good automotive oil like 10w30 or straight 30 weight oil is good. Once the chain gets kinky or rusty from lack of lubrication, it should be replaced before it does damage to the clutch sprocket. A new chain is a lot cheaper than a new clutch. If you keep the clutch and chain lubricated, you should get years of use out of both. Oiling the chain after it get dried out is a waste of time. Remember this is preventative maintenance, which means “before the items are ruined”.

Don’t put oil inside the clutch. The holes in the drum are to let hot air out of the clutch. Do not squirt oil in these holes! When oil gets inside the drum portion of the clutch it will cause excessive slippage, which means undue heat will be generated.

If your kart has a grease fitting in the crankshaft for lubrication, then a shot of grease once a month should be sufficient lubricant. The grease is coming from the inside of the sprocket outward, which is a better way to lubricate the clutch. The key way in the crankshaft acts as a reservoir for the grease, which cuts down on the frequency needed for maintenance compared to oiling the snap ring area. 

CHAIN MAINTENACE

The chain needs to be lubricated frequently to keep it from kinking. There are some excellent chain sprays available that are waxy and will not let sand and dirt adhere to them. Dirt and sand will wear that chain as well as the sprockets. 

All chain stretches over time. When the chain starts falling off the sprocket, it’s time to check chain alignment or move the engine forward or backward to take up the slack in the stretched chain. First, with the engine shut off, lift the rear end of the kart off the ground and safely set blocks under the rear bumper to allow for the rear wheels to turn freely. Now with an open-end wrench and socket wrench (most likely a 9/16” ) loosen (do not take them out completely) the four bolts that secure the engine to the engine mounting plate. Now pull back the engine until you take up the slack in the chain. Snug down the four bolts, but don’t completely tighten them quite yet. 

Before you tighten the four bolts completely, you need to check the alignment of the two sprockets - clutch and axle. You don’t want the sprockets out of alignment because this will cause the chain to continue to come off or cause excessive sprocket wear. With a straight edge (ruler, yardstick, length of key stock) set flatly against the rear axle sprocket, move it toward the clutch sprocket. It should line up exactly.  If the straight edge cannot be kept flat against the rear sprocket when trying to meet up with the clutch sprocket, twist the engine a bit until it does.

When this is completed, your just about ready to tighten down the four engine mounting bolts leaving about a ½” in play between the top and bottom of the chain. Don’t push or pull the engine so far as to get the chain as tight as you can get it.  An over-tightened chain also puts unneeded friction on the clutch bushing or roller bearing (if so equipped) which could cause it to engage when the engine is idling and can cause the kart to move with one in the seat. An over tighten chain will also cause excessive wear on the chain, sprockets and bushings.

Now, with the rear of the kart still on blocks, off the ground, rotate the rear wheels (and the sprocket and chain) by hand to check the tightness of the chain. Since no rear sprockets are 100% perfectly round, there may be a high (tighter) and low (looser) spot. You will find this area while rotating the rear sprocket. The tightest spot is where you want to adjust the chain to the ½” chain play as previously mentioned. 

Now, after you have a) aligned the sprockets, b) have found the tightest spot in the chain and c) adjusted the chain to ½” play, it’s now time to tighten the four motor mount bolts very tightly. When this completed, once more turn the rear drive by hand and make sure everything is working correctly. Now you can remove the block under the kart frame and you’re ready to go.

EDUCATE YOUR KIDS

Teach your children how to do the maintenance on the kart and accept responsibility for its upkeep. Good maintenance idea: Every second tank of gas is a good time to remember to oil the chain and the clutch bushing. If your child learns to do this preventative maintenance , the go-kart should be problem-free for many years. 

CLUTCH WARRANTY

How long will a clutch last? If the clutch is put on the crankshaft properly, without using the “magic hammer” to pound it on, using the correct length and style of key stock (1/2” in length x 3/16” square) and observing all the hints that are discussed in this article, a clutch should last many years. But, if it is improperly installed, driven in abusive conditions (sand, steep terrain, excessive weight in the kart, and others), the clutch might last only 20 minutes. 

As a clutch manufacturer, I will tell people to send us a clutch for review but if the shoes are blued (discolored from excessive heat), not to bother since we didn’t sell the clutch with blued shoes. If the clutch was misused or abused the tell tale signs will tell us what the possibly caused the problem. If you have a legitimate problem with your centrifugal clutch, contact the manufacturer. Most will be happy to try to analyze the problem and repair or replace your clutch. 

The author, James Donovan, is the owner of Max-Torque LTD, Melrose Park, Illinois. Phone: 708-574-7022. E-mail: info@maxtorque.com. Web: www.maxtorque.com.
 

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