Help required on non A g/box

[Topdad]

hi guys , hope you don't mind a non a10 question? But at least bsa orientated . my mates finally got a  frame for his rigid b31, and then discovered that the box we'd rebuilt was not going to be any use to him. Undaunted by this he only produces another box he's had for years and asked me to check it over. Can't post piccys yet new phone not playing but sure someone will know what I need.
It's mounted to frame by 2 lugs at the bottom roughly at an inverted "v"the end cover is bigger than an A and inside the positive stop mechanism is bolted to the inner cover , real work of art!  And changes gear by way of pivoted adjustable rod. I can only get 3 cogs and neutral seems to be found with the arm sitting on top of the ratchet like part. All seem to work well .So to get into the bowels do I put her in neutral as per ours ,any thing else I should watch out for and is it only a 3 speeder or just in need of cleaning etc. I hope someone ,no I 'm sure one of our single inspired members can help, thanks BobH

[Triton Thrasher]

Is this it?

[KiwiGF]

I have rebuilt a b31 rigid box and its very similar to the a box except the way the selectors are moved as you have noticed.

if its got 4 pairs of gears its 4 speed, I thought even early b31 are all 4 speed?

My advice is to check for wear on the small parts in the  gearchange mechanism and also that the neutral stop is working as it should....oh and.assemble the clusters in the neutral position.

the same sites with a service sheets have the b service sheets includ I ng those for the box.

good luck!

[Brian]

The gearbox in TT's pic is the four speed out of a C11G, most of the internals are interchangable with a A series plunger box.

There are a couple of different boxes for B31's depending on the year. The immediate post war '46 and '47 was a light weight box and the mounting lugs underneath are only 2" wide. The "later" box is of a heavier construction and the lugs underneath are 2 1/2" wide. Both boxes are 4 speed.

The adjustment of that pivoted rod is critical and sometimes it can take a couple of goes to get it right.

I'll add a couple of photos and if you look carefully you will be able to tell the two boxes apart. The silver bike is my '47 B31 and has the earlier type box, the red bike is my '49 B33 and has the heavier type box.

[Topdad]

Many thanks all of you ,that's given me more than a start! Brian it seems to be the same as on your '47 red bike (. Very nice by the way) I'll show Bruce the bikes that should get him something to aim for!! Mind if I pm you if I get stuck oh and in neutral should the ratchet sit on the top of the tooth ?many thanks to all once agin regards bobh

[Brian]

The red bike is the 1949 one, does he have that gearbox ? If you work out exactly which gearbox he has I will scan the service sheets for that model.

[Topdad]

Many thanks for your offer Brian. Sorry its taken me to days to respond no disrespect intended due solely to family presure coming before fun! If I could sort my new phone out I could e-mail some pics but that will have to wait. I'll have a good look at it tonight and e-mail you the ID on the box thanks again BobH. Ps have you heard of any other motors being fitted in a ZB frame?

[Brian]

As far as I can work out there are about 16 different models using a ZB frame, from the standard B31 through to the Goldstar.

If your mates frame is a ZB frame it will have the same gearbox as my '49 B33 (red one). The '46 and '47 frames and engines are prefixed with a X and 1948 with a Y. Z was the prefix for 1949 through to 1952.