Go Kart Drive Line components can be quite expensive, especially if you are thinking of making your own reliable budget go-kart. Typical transmission line component costs can range from $ 100 to $ 200. However, the inexpensive alternative to the traditional clutch and chain drive system is the belt drive.
The basic belt drive consists of a driver on the motor and another driven on the wheel or drive shaft. The belt is tensioned by moving the engine forward or by pressing a belt tensioner on the belt.
There are several important requirements for a belt drive. First, the right proportion, and second, the components of the right type.
Go Kart Belt Drive Ratio
The belt drive system to work requires a steep 8: 1 ratio. A lower ratio and the engine will stall and the go-kart will have to push it to run. (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 engine will stall or the belt will fume.
Proper selection of components
One of the big mistakes first time kart builders make is using a pulley made of zinc. These pulleys can usually be found in hardware stores; however, they cannot handle the power requirements of go-karts. In fact, if you use a pulley made of aluminum or zinc, the pulley will melt after about ten minutes of use. The pulley must be made of steel.
The next important design criterion on a motor pulley is that it should be as small as possible. A 1.75 bore is as large as possible before the ratio goes out of range and the engine stalls and fumes from the belts.
Also, the pulley will get very hot and must be held in place with Loctite and a bolt on the end of the motor to prevent it from coming off the motor. And, obviously, the pulley must be coupled to the motor to ensure adequate torque transmission to the pulley-belt.
The driven side of the kart is a completely different matter. The pulley can be made of sandwich plywood as a low-cost homemade alternative, or the pulley can be purchased at a local tractor supply store. The wooden pulley is attractive because it is very cheap and can be mounted directly to a wheel using bolts.
The belt tensioner system requires some durable tensioner pulleys. These can also be purchased at a local hardware store. The belt tensioner is basically a pulley that gets stuck in the face of the belt, causing the belt slack between the motor drive and the wheel pulley to decrease. This now taut 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 engine 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 winding; And that’s the key to belt drive – at least 180 degrees or more of belt wrapping around the motor pulley.
The idea is to get the largest gripping surface 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. Typically, a spring is used to deactivate the system, so when the clutch is disengaged, the engine does not spin the tires.
Important note about belt tensioners
This is an important note about belt clutch systems. Always have the system shut down only when no human intervention is taking place. For example, the foot releases the pedal, the clutch is released automatically. The reason for this is that if the engine is being started, the last thing you want is for it to be in gear. This will cause the kart to move forward during startup. Again, it is important that the clutch system is automatically disengaged.