Hey gang, a quick update - took us a full day and a half to build it, but she's done and runs great! Took it to work this morning, and I'm hooked. My son wants one too, so I told him in a month or two I'll see about getting another engine for his OCC Stringray, which would be sweet (I was tempted to snag it for this build, actually, but I knew he'd be pissed LOL).
OK, someone asked if a trek 3700 would work. If it's got an aluminum frame with the fat downtube, forget it. You have to drill a hole to mount the motor on that frame and it'll probably crack on ya with time. We had that problem with the trek, and we solved it by using an old Diamondback Wildwood my dad had laying around instead of the Trek. When we stopped by walmart and target for the additional stuff I needed, we looked at the bikes they had there - nearly all of them have these fat downtubes now. You need the normal size ones like what you'd find on a tenspeed or something unless you want to fabricate your own mount or drill holes which I don't recommend doing on an aluminum frame. If you know someone with a welder, that's an option I suppose - don't know about that.
Also the directions that came with this motor should be labeled "suggestions" instead. Jeez, what a mess! These are better: http://www.usabikemotors.com/download/enginemanual.pdf
but even with these, it's best to have someone with mechanical aptitude to help if you're a total small engine noob like me. The extra pair of hands comes in handy too.
I'll be posting pictures later in the week in the Mountain Bike section, so everyone can see how it turned out. Pretty cool, overall. My son's stingray will be even cooler looking when we get that done. Great hobby! Love it!