Hi, I live in Belgium and I have a question about my M20 gearbox.Excuse me for my English language but I hope it 'll be clear for you.
I'm going to rebuild an M20 gearbox. It was a spare gearbox and I don't know if he was in working order.
I stripped all the parts and I inspected the parts. They don't look worn.
But I have a question:
-When I place the layshaft into the gearbox shell and close it with the inner cover (4 screws)there is a side play of about 2 mm on the layshaft. I can move the shaft 2 mm between the bearings. (with my hand in the inspection cover)
-When I put the mainshaft in the shell it's the same side play of 2 mm. I can move the mainshaft 2 mm when I pull on the shaft.
-The gearbox control shaft (with forks) has no side play.
Is this side play on these shafts important and what is the correct side play?
I hope someone can help me.
BSA regards from Belgium.
Eric

email (option): ericvangils@skynet.be

eric
heb ook juist een gaerbiox in elkaar gezet en heb geen speeling op de hooftas eric.ook van uit belgie.

Hi Eric, the end float on all three shafts should be around .005"-.010". To reduce the end float on the lay and selector shafts place shims behind the bushes. On the main shaft shims can be placed between the fourth gear and the main bearing. At the kickstart end shims can be placed between the bearing retaining washer and first gear.
Check the side of the selector forks and the groove in the selector dogs for wear or blueing and make sure that when the box is assembled that the selector dogs sit centrally between the gears when in neutral.

Thanks Matty for your advice. It's very interesting for me. Do I have to use a paper gasket between the inner shell and gearbox shell or only use some compount?(silicone)
Greetings, Eric

email (option): ericvangils@skynet.be

Hi, they do have a thin paper gasket on the end cover, both the inner and outer covers but there is nothing wrong with using silicone if it helps to get the end floats correct

email (option): davmax@ntlworld.com