[Ratters]

I like to remove everything from the gearbox shell during shimming.
The first gear (spur) generally uses a very thin shim to keep it from bottoming out against the shell

Then you can build the shims on top, put the gearbox together, hold it firmly together or screw it snug and do a push test on both shafts through the bearings

It's OK to have a fraction of movement

[Don't forget to clean out the old grease and feel for metal, if there's metal inspect your gears closely and your piston rack, cut off lever, anti-reversal latch]

Repeat with the second gear, (sector)making sure it just clears in mm the bottom gear, again, build it up, screw together, check for lateral slop, shim accordingly

gears slightly different, depending on the motor gear and drive gear, motor gear and drive gear teeth or mesh heights can vary

I like to put this gear up against the motor gear to see what type of mesh depth I get

This last gear (Bevel) can sometimes benefit from a few more shims under it, opposed to above it to help motor gear engagement be more integrated

Once these are all in and you've screwed the shell together use a thin dowel or screwdriver to check for free spinning. Slight resistance is ok, spinning with very little resistance is ideal providing lateral shaft movements are in the thousands

Now open it and put your piston in, close it up and make sure it's moving freely, not binding between the shell halves

If it's good do the same with the tappet plate

If all of this goes well you've got a smooth moving gearbox, reassemble, be aware your motor height is now different so test and adjust accordingly

You can also do an AOE mod at this point, or not

You should now have a gearbox that will give you reliability for a long long time

While the motors out its also wise to check for wear on your motor brushes and commutation

Hope this helps