I am putting together an older doodlebug mini bike and need a new clutch for 3/4" shaft. My question is what amount of teeth on the clutch is needed for the bike which already has a 70 tooth sprocket on the rear? Any thoughts? I know it most likely has to do with ratio and either low end torque or top end speed, but what would you recommend for a basic mini bike build?
All of the information I will give here is based upon the common DB30/Predator 212 swap.
The engine that bike came with did not have a lot of power. That is why the 70 tooth rear sprocket was used. When we add power to that bike, you will have a wheelie machine with the standard 12 tooth clutch. A 12 tooth clutch will be good for engines with 5HP or less
If you are using a 6.5HP OHV engine, I would recommend the 14 tooth clutch to give you a 5:1 drive ratio. This will give you a "happy medium" for take-off power and more speed...and tame the wheelies!
You will also need a key.
We don't want to use set screws on these clutches. It is easier on the clutch and chain if the clutch is allowed to "float" on the crank. It will self align. Use this clutch bolt for cranks that are drilled and tapped. The only time we use set screws is with cranks that are not drilled and tapped