Motor bike idler re-design

The idler kit for these cheap motorbike kits is pretty lame. Notice the clamp that grabs the chainstay and the slot the idler pully has to move up to tension the chain. This setup seems to let the chain loosen up after about 5 minutes of riding time. The nylon pulley is probably not nearly as satisfactory as an idler sprocket would be but that upgrade will have to wait for later. My current effort has been centered around the mounting and adjustment portions of the idler system.

Here is what I came up with. The new unit uses a swing arm pivoted from the bottom rather than a slot for moving the pully against the chain. Note the welded on tab on the chainstay and on the seatstay where an adjustment screw can be hand tightend and then locked with a wingnut to pull the chain into the desired tension. I'm thinking that having the tensioner setable without tools will enable the chain to be removed from the sprocket out on the road, making the bike much easier to roll back home should the motor quit (hope for the best, plan for the worst).

4 stroke bike

This project came about when my son sent me home with a bike motor kit and asked me to turn it into a motorbike. The motor is a 48cc 4-cycle with centrifugal automatic clutch. A friend gave me an old Phillips 3 speed frame and I had a heavy duty fork in the shop as well as some steel 26" wheels and some extra tires. The motor is fairly smooth and quiet and pulls up hills pretty good, which is fortunate as there was not room enough for pedals to be installed. The gearbox generates some whine and the chain idler will need some improvement but the finished product shows promise as a fun little motor bike.