ok,
Now i feel like an idiot.
I can't find a search feature to search previous posts.
Maybe it's hiding in plain sight.
Here's my situation/questions:
I've been thinking about motorizing a mountain bike or 2. If I do this my wife will want one.
I'd like a 4 stroke to minimize noise, smoke, etc.
I don't know how well a friction drive would work for me, we have lots of sand-gravel roads.
I may look at a chain or toothed belt drive.
It seems the easiest way is to mount a chainsaw to the rear rack and use the existing clutch (I have an old 75cc echo in my garage). Not very elegant. Really loud. Can't start it with inertia.
I've been looking around at 4-stroke weed-eater type motors. Will the 40cc briggs handle a cantilevered pulley or sprocket (or friction wheel) or do I have to fab an outboard shaft bearing? Is there some reason to avoid this engine?
Also, Is there some simple, cheap manual mechanical clutch available that can fit on an output shaft?
As far as a motor mount, I've been planning on converting a blackburn 4-point aluminum rack. I've got a couple around from years ago, and if it will hold 4 cases of beer (don't ask) it shouldn't have any trouble with the weight and loads from a small engine.
I've also been thinking about fabricating a really long flow path (quiet without too much restriction) muffler, but that will come later.
Thanks again all.