The motor and drivetrain. This is a Honda GX 35 35cc, 4 stroke engine, rated at 1.5 HP. The gear reducer is from Staton Inc.. It's a bit heavy, but really well built and very quiet and efficient. I like this set up a lot because the weight of the motor and gear reducer is low, they're very sturdily mounted, the motor drive chain is easily adjusted by sliding the gear reducer back and forth in the engine mount slots, and the drive chain is nice and short. Gearing is easy to adjust by swapping different size cogs or BMX freewheels. The jackshaft is a 5/8" keyed steel shaft with special adapters from Staton Inc. to mount the freewheels on the shaft. Because freewheels are used, riders can pedal independently from each other or the motor, or not pedal at all. The motor can be used with or without pedaling.