Transmission, or gear box for 40cc 4-stroke motors. Comes with the stock 11-tooth pinion gear attached.
Typical symptoms that indicate a gearbox:
- Your bike started making a terrible rattling noise in the engine.
- Rear wheel is locked up, when pulling on the pull start the back wheel immediately starts spinning.
To replace the gearbox, you have to remove the four screws that hold the transmission housing on to the engine. Use an 8mm socket wrench to remove the bolts and wiggle free the transmission case.
While you're in there, look at the clutch. Sometimes the spring in the clutch breaks. Sometimes, the nut from the gear box falls off, and damages the clutch in the process.
If your spring broke, make sure you look carefully inside the engine cavity to make sure there are no pieces of the clutch spring remaining, before installing the new clutch.