dismantling 1930's four speed gearbox - advice appreciated

[Ian Dabney]

I am having problems selecting 1st gear on a heavy weight 4 speed gearbox (attached to a S6) and would appreciate help as to how to take it apart, ideally with the box in-situ on the bike. I have removed the gearbox front cover, bendix style kick start mechanism, removed the 3 retaining screws holding the middle case and loosened the selector shaft gear off its keyway. The middle case is loose to move a little, but will not come off. Do I need to remove the primary and drive chain sprockets or any other items? Once free to open, should I expect it to come out in one bit or 10's of bits dropping on the floor?
many thanks
Ian

[Doug]

Ian,

The intermediate cover should come off along with all of the gears and the shift cam drum. Once you have taken out the countersunk screws (including the one behind the rack), remove the detent plunger for the cam drum, and the input sprocket from the main shaft. Then it should only be the lay shaft journal with a light press fit in the layshaft ball bearing holding it in. There is no need to remove the shift cam drum pinion.

The attached photos are from a 1936 Aero 4-speed, but the S6 gearbox should be quite similar.





-Doug

[Ian Dabney]

Doug,
Many thanks - the photos are also a great help, will give it a go today,
regards
Ian