I am using a custom machined clutch adapter that bolts to the four bolt pattern on the PTO side of the engine- and a three-shoe 77mm clutch rotor- you have to cut the crankshaft off to a stub and then key it to fit the clutch rotor. It works very well though- with the modification I did, you can then use any of the clutch housings like for the chain drive scooters- (go-ped GSR40). My gear reduction is a 9 tooth on the clutch housing to a 120 tooth on the rear hub of the bike- on the left side of the hub with a left handed freewheel of course. I can pedal, or use the engine, or both at once.
I'm using #25 chain.
Send me an e-mail address and I'll shoot you a picture of it.
[email protected]