Go Kart Drive Line components can be quite expensive, especially if you are thinking of making your own cheap and reliable go kart. Typical driveline component costs can range from $100 to $200. However, the economical alternative to the traditional chain clutch driven system is the belt drive.
The basic belt drive consists of a drive on the engine and a drive on the drive wheel or axle. The belt is tensioned by moving the engine forward or by pushing a belt tensioner on the belt.
There are several important requirements for a belt drive. First, the right ratio, and second, the right kind of components.
Go Kart Belt Drive Ratio
The belt drive system requires a steep 8:1 ratio to work. Any less and the motor will stall and the go kart will need to be pushed to get it going. (This 8:1 ratio assumes the wheel is 12 inches in diameter.) The general rule of thumb for pulley size is that the driven pulley should be as big as the rim. If it is less, the ratio will be too small and the motor will stall or the belt will smoke.
Proper selection of components
One of the big mistakes first time go kart builders will make is using a pulley made of zinc. These pulleys can usually be found at hardware stores; however, they cannot handle the power requirements of karts. In fact, if you use a pulley made from aluminum or zinc, the pulley will melt after about ten minutes of use. The pulley must be made of steel.
The next important design criteria for a motor pulley is that it should be as small as possible. A 1.75 bore is about as far as you can go before the ratio goes out of range and the engine stalls and smokes the belts.
Also the pulley will get very hot and needs to be held in place with Loctite and a bolt on the motor end to prevent it from coming off the motor. And obviously the pulley must be coupled to the motor to ensure proper transmission of torque to the pulley belt.
The driven side of the go kart is a completely different matter. The pulley can be made from sandwich plywood as an inexpensive homemade alternative, or it can be purchased at a local tractor supply store. The wooden pulley is attractive because it is very inexpensive and can be mounted directly to a wheel using bolts.
The belt tensioner system requires some durable idler pulleys. Those can also be purchased at a local hardware store. The belt tensioner is basically a pulley that is stuck to the face of the belt, causing the belt clearance between the motor driver and the wheel pulley to decrease. This now tightened strap grips much better and makes the wheels turn.
It is important to be on the slack side of the belt when using a tensioner; otherwise you will be fighting the motor and constantly burning the belts. The way to see a belt is to see it as a glorified rubber band. The belt stretches as it passes over the motor pulley.
The tension side will always be tight, but the slack side tensioner encourages full belt wrap; and that’s the key to belt drive: at least 180 degrees or more of the belt wrapped around the motor pulley.
The idea is to get the largest gripping surface area for the belt so that it transfers the load efficiently through and to the rest of the drive system.
The tensioning system can be activated by a lever arm or a cable. A spring is usually used to deactivate the system so that when the clutch is released, the engine does not spin the wheels.
Important note about belt tensioners
This is an important note about belt clutch systems. Always have the system turn off only when no human intervention is taking place. For example, the foot releases the pedal, the clutch automatically releases. The reason for this is that if the engine is being cranked, the last thing you want is for it to be running. This will cause the go kart to lurch forward during startup. Once again, it is important that the clutch system disengages automatically.
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