The gearbox on my recently purchased rigid 1948 B33 is different to those that I have on my M and later B series bikes. Am I correct in assuming that this is the 1946-1948 type of gearbox? I haven’t come across one of these before with the speedo drive by the drive sprocket. Are there any peculiarities that I need to look out for when working on it?
Here are a few pictures of a spare that I got with the bike.
Cheers
Pete
This box was a further development of the light weight box fitted to pre war B Models and the 1940 B29...
As such it shares many, but not all, of the internals of that box...
Overall construction is far lighter than the later M and B type rigid/plunger boxes though the operating principles are the same...in fact it is a scaled down version of the heavier box, including a smaller main bearing..
Access to the kick start return spring is not as easy as on the later types and generally the lighter construction means they have not stood the test of time so well if they have high mileage on them..So expect to find more wear than might be expected in an equivalent age/use M20 box...
Interestingly the gear change ratchet and pawl assembly is the same as the M20...
Adjustment of the shaft end float is done by the use of differing thickness bronze and steel spacers rather than by using shims as in the heavyweight box..
If you have a spare box that is a good thing as spares are harder to source than they are for the other types..
Funnily enough I've just been offered a B33 project of the same year....
Here's a picture of the internals of the earlier version that I restored..Ian
email (option): ian@wright52.plus.com
I have some info. on the earlier box, which is essentially the same regarding set up of the shafts...Not sure if I have a 1946 maintenance manual...I'll have to have a dig through my paperwork for that...Ian
email (option): ian@wright52.plus.com
Hi Ian.
Thanks, I would appreciate any info.
The more I know before messing 
with the thing the less damage I am likely to cause.
Cheers
Pete
Here from sheet 306
"Slack off the large nut on the drive and give the end of the drive a tap with a hide mallet. Remove the locating screw.
The large nut can now be used to withdraw the drive, distance pieces being built up behind the nut until the drive is fully withdrawn."
Haven't done this myself on this box but I think you can see the head of the locating screw (hex head) on the second picture in the first post above.
Pete
I have this 46-48 gearbox if anyone is interested. Mostly complete.