Are you asking if you can put a chainsaw or weed eater engine on a bike, *using* a chain drive? or are you saying you want to put the engine on a bike that has a chain drive from the pedals to the back wheels? Every bike I've ever seen has a chain drive for the pedals, so I think the answer to that question, can I put a chainsaw or weedeater motor on a bike, is an overwhelming yes. If you want to do a chain drive from your motor to your back wheel, you'll need a fairly large sprocket, nearly the size of the back wheel.