My little brother got an old 2.5hp 2t snowblower for free, it was too small for us to use, so it sat in our barn until he got the idea to mount it on a small bike. He mounted the motor inbetween where your legs would go. He made a shaft to go into the petal housing. I pressed in some old bearings so the shaft would turn, he welded a bicycle sprocket to the shaft, and then a spacer to the outside of the sprocket. He Drilled and tapped the spacer and bolted on a lawnmower pully. Hooked up the old bicycle chain and then bought a belt to hook straight up to the motor. It was geared to high tho. It worked really good, he even rigged up a clutch using a brake cable and a lever to dissengage the belt using an idler pulley, like on a lawn tractor. Just slip the heck out of the clutch and go! It still sits in the barn if I recall. It was a lot of fun and a good project for a 12yr old.