homemade gearbox? sorta?

you might be onto something let us know how it turns out .

I cut the 3 speed trans out of a broken Royal Enfield 125cc years ago planning to use it with a Whizzer motor on a Schwinn. Had flat mounts welded to it but never used it. I removed the kicker and sealed the hole for a pedal start. It has a dry clutch hanging on the left side. I'll dig it out and take another look at it soon.

Great idea!
I've always wanted to find a small manual clutch trans for a bicycle.
Very interested in how it works out!

Hmmmmmm....... Mah gears be a turnin!

Rick,
I would think that as long as the transmission has a dry clutch it would work OK. My understanding always was that they went to the one piece engine-transmission combination because that it was cheaper to combine the two to make and to install them all in one piece rather than have two mounts to deal with when they were putting them into the frame.

It will be interesting to see what you come up with.

Steve.

Remember our gears are 15mm bore, if you want to use a 17mm bore (more common with moped cranks), you can use 6003 bearings, they'll slip right in and give you a better balanced crank, possibly a larger wrist pin and maybe a longer conrod (might need a spacer), but some mopeds have gears so the 17mm would be your best bet. problem is... the spacing between the clutch gear and the drive gear likely wont line up. I've been trying to think of a way to do a transmission; direct bolt-on for our motors, but I'm not familiar enough with the gearing and clutch system of... well basically anything, it would have to be workable either with foot pedals or with a bicycle gearing system, and would more than likely cost more than the SBP kit but for the solid gears and ease of use, it may be worth it.