This is specifically aimed at 1 cylinder and /2 gearboxes.

If you’ve tried everything and you can’t figure why the gearbox shafts do not turn freely, you can use following very time consuming method  🙂 to determine the cause:

Instead of putting all 3 shafts in at the same time, put in 1 shaft at the time.
Remove the input shaft seal from the gearbox: the seal makes it harder to rotate the input shaft, making it difficult to assess whether the shaft is running freely.

Remove the idler gear and kickstarter gear segment.
Whenever you install (and remove) one of the shafts, you need to warm up the gearbox and gearbox cover. (up to 80 C)
The assembly of a shaft or the cover must be done as quickly as possible so that the bearings can set themselves freely.
If the bearings (especially in the cover) get stuck during assembly, the 2 opposite bearings will be pushed towards each other, which will lead to (slight) jamming of the shaft.
If it does happen, lightly tapping the front of the input shaft and the back of the output shaft with a hammer may help.

Make sure all bearing seats are completely clean.

1. Heat up the gearbox, install the input shaft, without any shims. Make sure the bearing is fully seated in the bearing seat.
While heating up the gearbox cover, let the gearbox cool down.
Put the cover on the gearbox, including the gasket. Tighten all nuts of the gearbox cover.
Let the gearbox cover cool down.
If the shaft turns freely, you know it’s not the bearings that are too tight in the bearing seat (gearbox case and gearbox cover)
2. remove the gearbox cover and add the shim thickness that you calculated or that was originally installed.
3. put the cover back (including gasket) and tighten all nuts. Let the gearbox cool down.
4. check if it still rotates freely.
5. remove the cover and replace the shim with the next thicker shim. Repeat steps 3 and 4.
6. keep replacing the shim with a thicker shim until you notice that the shaft does not turn freely anymore. The last shim that allowed the shaft to turn freely is the correct one.
7. repeat the steps 1 to 6 for the other 2 shafts. Since the output shaft is not installed, you can reach the intermediate shaft via the hole for the output shaft in the cover
8. When done, install the input shaft and the intermediate shaft together. Check if they rotate freely
9. Then remove the input shaft and install the output shaft. Check if the intermediate shaft and output shaft rotate freely.


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