Idle Gear 40 teeth 2nd gear / 4-speed gear Simson

Transmission gears

The gears of the transmission must be in excellent condition so that the gears can shift smoothly.
If you have problems shifting gears, it is possible that the gears are damaged. If the gears are worn, you will find metal shavings in the oil when you change the oil. If a gear breaks off completely, the transmission will lock up.
When you open the engine, you can check the condition of the teeth and see if they show any grinding marks or are rounded instead of sharp.

The easiest way to change the gear ratio is to replace the rear and front sprocket, but of course you can also replace the complete gearbox (e.g. for 50cc bikes with AM6 and Derbi engine).

Repair gears or buy a new one?

Repairing gears is not that easy. You need the right tools, and you need to have sufficient knowledge about the materials to repair the gear so that it is robust enough to do its job. Just use new gears instead!

Transmission does not work

It's not necessarily the gears that are responsible for a gearbox failure. It is best to check the shift drum, gear selector fork, bearings, etc. as well.

Our exploded views will help you find the right spare part.