Hi everyone,
I'm currently working on getting a 1946 B31 back to life.
The early B31's had a different gearbox to the later ones (after 1949, I believe) which became common with the M range. I've had very little luck finding parts or indeed a complete gearbox for my bike. Unfortunatetly the later gearbox does not fit the earlier frame as the distance between the plates increased.
My question is if the internals of the later box also changed, or if they could be used in the earlier cases. Are the bearings, shafts, gears, etc the same, or is everything completely different?
Thanks,
Gui
Hi Gui,
There are differences, check here its a good comparison:
https://www.draganfly.co.uk/product-category/bsa/sparesparts-for-bsa-a710-b3133-c101112-m202133/engine-gaskets-gearbox/gearbox-abcm/b-m-group-1938-62-plunger-rigid/
I was supplied a 1946-48 gearbox for a 1953 season bike. Due to the difficulties getting spares I have obtained a 1949-62 box, once I have rebuilt it the earlier will go on Ebay. I will let you know when this happens (waiting for the weather to warm up, its too cold in my garage).
Best wishes...
Hi GUI
If i were you I'd go on the Draganfly website and study their exploded diagrams of gearboxes.
They often give date / type details and practically all the OEM part numbers - so you can work out what you have and what you need.
Pete
https://www.draganfly.co.uk/product-category/bsa/sparesparts-for-bsa-a710-b3133-c101112-m202133/engine-gaskets-gearbox/gearbox-abcm/b-m-group-1938-62-plunger-rigid/
Thanks,
Yes Drags is a big help, but I was wondering if purchasing a complete gearbox might be easier. Of course, only if the majority of the internals are the same.
But if someone has one of these earlier boxes, do let me know. Keep me in mind Bess!
Cheers,
Gui
Hi Gui,
Okay will do, this is what I have. The gear change linkage is missing but available from Draganfly.
I just need to make sure mine is okay first, in case I need to use the later as a donor (I used the linkage). I doubt I will need anything further as bought new springs, bushes, shims and clutch lever ready to start the rebuild. Once I'm ready I will list what's missing so you can decide, I've PM'ed you so we are in contact.
Best wishes...
I have a gear change assembly if it is like the dirty brown thing in top right of picture, it's yours for free, it's been soaking in a fuel/oil mix for 2 years, should be ok, might need new return springs.
I rebuilt one of these gearboxes last year. I bought a B31 at auction, supposedly running well. It wouldn't select 2nd gear when running.
Due in part to too much end float in the shafts. The main problem though was the spacer on the selector shaft was missing. I found when the box had been rebuilt earlier that the 4 screws that fit the front cover from the rear( hope that makes sense) were cap head screws. I couldn't get them out with the gearbox in situ, as the Allen key wouldn't turn enough to undo them . They need to be hex head screws, as you may need to make adjustments to the linkage, which means taking the front cover off. The kickstart spring is a challenge!
Apparently it is possible to fit a later gearbox to the 46-48 frame if you are prepared to modify the gearbox lugs so that it fits between the narrower mounting plates.
I am considering this for my 1947 B33 as, despite a full rebuild, I am still having minor problems selecting 4th gear and the clutch is a pain. Although I have had no real problems with a B31 fitted with the 6 spring clutch (once set up with a dial gauge!). Cases for the late boxes are not in short supply so even if it doesn't work out it won't be a major financial investment.
You can only use a 6 spring clutch on the 46-48 gearbox due to the different mainshaft, the later mainshafts allow the fitting of the 4 spring clutch. Also the winters are long here in Germany and I need something to do!
Of course the main advantages of switching to the later gearbox would be not having to deal with the #*@ing kickstart spring ever again!!!
The clutch hub on the earlier box is different as the shaft taper is shorter and a different angle.
If you fit the later box it is very awkward to get the box position adjuster to fit in place.