Advice on buying an engine kit... anyone?
Hey all, my son is 15 and I'd like to get him an engine kit to make a motorized bike. Problem is that neither he nor I know anything about them. He's got 2 nice mountain bikes, so we only need the engine... but which one should we get? Are the cheaper ones worth it? What should we stay away from? Any input would be really helpful seeing as this is my first foray into mechanics.