drive shaft

For friction drive...

Was planning on rigging a weedwacker engine to my bike, but not sure how to rig the chain up. How do you direct drive people do this, without any welding?

I'm using a 25cc weed eater motor (poulan). After removing the plastic casing and pull start, I see the drive shaft. But there is a disc at the base of the drive shaft that spins with the shaft. It has a magnet piece that rotates by a little black box. The black box has the spark plug wire...