Go Kart Drive Line components can be quite expensive, especially if you are thinking of making your own reliable cheap go kart. Typical costs for drive line components can be in the range of 100 to 200 dollars. The cheap alternative, however, to the traditional chain-clutch driven system is the belt drive.
The basic belt drive consists of a driver on the engine and a driven on the drive wheel or axle. The belt is tensioned either 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 proper ratio and second the proper type components.
Go Kart Belt Drive Ratio
The belt drive system in order for it to work requires a steep ratio of 8:1. Any less of a ratio and the engine will stall and the go kart will require pushing in order for it to go. (This 8:1 ratio assumes the wheel is 12 inches in diameter.) The rule of thumb for the pulley size is that the driven pulley needs to be as large as the tire. Any smaller and the ratio will be too little and the engine will stall or the belt will smoke.
Proper Component Selection
One of the big mistakes that first time go kart builders will make is to use a pulley that is made out of zinc. Typically these pulleys can be found at hardware stores; however, they are not able to handle the horsepower requirements of go karts. In fact if you do use a pulley that is made out of aluminum or zinc the pulley will melt after about ten minutes of use. The pulley needs to be made out of steel.
The next important design criteria about an engine pulley is that is needs to be as small as possible. A diameter of 1.75 is about at large as you can go before the ratio becomes out of range and the engine stalls and smokes belts.
Additionally, the pulley will get piping hot and needs to be held in place with Loctite and a bolt on the end of the engine to prevent it from coming off of the engine. And obviously the pulley needs to be keyed to the engine to ensure proper torque transmission to the pulley-belt.
The driven side of the go kart is an entirely different matter. The pulley can be made of sandwiched plywood as the low cost homemade alternative or the pulley can be bought at a local tractor supply store. The wood pulley is attractive because it is very cheap and can be mounted directly to a wheel via bolts.
The belt tensioner system requires some durable tensioner pulleys. Those too can be purchased at a local hardware store. The belt tensioner is basically a pulley that is jammed into the face of the belt causing the belt clearance between the engine driver and the wheel pulley to lessen. This now tensioned belt grabs much better and causes the wheels to 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 up belts. The way to look at a belt is to view it as a glorified rubber band. The belt stretches as it passes the engine pulley.
The tension side will always be tight, but the tensioner on the slack side encourages full belt wrap; and that is the key to the belt drive: at least 180 degrees or more of belt wrap around the engine pulley.
The idea is to get as much surface area grabbing the belt so that it efficiently transfers load through and to the remainder of the drive system.
The tensioner system can be activated by a lever arm or a cable. Usually a spring is used to deactivate the system so that when the clutch is unlatched the engine is not spinning the tires.
Important Note About Belt Tensioners
This is an important note about belt clutch systems. Always make the system deactivate by itself when no human input is being done. For example, the foot releases the pedal, the clutch automatically releases. The reason for this is if the engine is being started, the last thing you want is for it to be in gear. This will cause the go kart to lurch forward during start up. Again, it is important to have the clutch system deactivate automatically.