Full Z155 Gearbox swap and modification Video coming soon

The Zongshen Z155 has a reputation for jumping out of 3rd gear. There are a few ideas of what to do to stop it or at least minimise it happening.

The gear dogs are not machined and have a radius at the root of the dog. This makes the gears spread under load and increase wear on the selector forks massively. Three of our 4 bikes have had this modification done and the only one not done is the totally stock demo bike. All of the tuned bikes have had this done. My own personal bike had between 5 and 7 hours on the engine before it started to jump and need to be swapped. The engine now has about 12 more hours on it with no issue. I rarely use the clutch for gear changes and know over winter it will need a new set of gear selector forks which cost less than £8.00 if you just swap the forks and not the selector drum too.

You can see in this video how far the gears will be pushed sideways under load before the modification. Once the modification has been done there should be zero sideways movement.