Just built these motorized bicycles one is a Mongoose Manuver the other is a Specialized Milano. The Mongoose has a 49cc 4-stroke with a Grubee gear box, rubber mounted engine, custom exhaust. Specialized has a 48cc grubee Star-fire slant head rubber mounted engine, head reversed, head gasket removed, wide crank arms. The Specialized needed the front motor mount trimmed to fit the frame.  Find out more about motorized bikes visit http://www.greenspinner.com