Help needed with Friction roller

You might try that's dax

http://thatsdax.com/KIT_FRICTION_DRIVE.html

Deacon is the expert on these things, you might get some ideas looking
at his old posts.

The Dax kit requires a 76mm clutch bell. His clutch looks like it could be smaller.

Homemade Dax type drive using trimmer clutch:
http://www.motoredbikes.com/showthread.php?15845-Full-build-details-on-my-home-made-friction-drive

Hi Peter, I have been using an 13/16 socket that I rough up with some sand paper and hack sawed some x-shaped grooves into it, so far it doesn't work to bad.

Hi peter,

If you want to use the existing weedwacker clutch make sure you pedal up to a fair speed before applying throttle, these clutches use metal-on-metal contact and are not intended to slip while transmitting power. You need a clutch with friction material on the shoes to start from a standstill. The all-metal clutches will either weld themselves together or wear out very quickly while making a deafening screeching noise

Also keep in mind that, if you homebrew your roller & mounting bracket, that the roller needs an outboard bearing--just putting a roller on the crankshaft and letting it stick out is asking for trouble. Ideally, the roller has its own 2 bearings, one at each end, with the tire between them, and the engine's crankshaft sees no radial load from the contact pressure of the roller on the tire. You can use a timing belt to drive the roller from the engine's crankshaft, this gives some pre-reduction which allows a much larger roller diameter, giving a larger contact patch between roller and tire--reducing wear and 'chewing' of the tire.

Have fun

Ian