B21 gearbox endfloat

[Greenfield]

With new kickstart bushes fitted, I've carried out a dry run of reassembly. With the inner case fitted without a gasket, there's significant endplay in the mainshaft. There's a thrust washer inside the inner gearbox case. Are different thickness of thrust washer available, or shims, or is there something else that could be an issue?
Many thanks in anticipation.

[militaryron]

For the M20 box, packing shims were available in 5 and 10 thou thick. I've been able to buy the 5 thou in boxes of 12 from Russell Motors. These are 3/4" ID and 1 1/4" OD. If you've never dealt with old Les at Russell's before. He doesn't do email and best to phone him Tue-Thurs 10-4. Ron

[Rupert]

The B series gearbox mainshaft has 5 washers which can effect its position in the box and its endfloat.
From the kickstart end -

There's a washer 65-3117 between the kickstart ratchet nut and the inner cover. This needs to be the correct thickness to position the shaft so the selector fork and dog is exactly in the middle between third gear and the sleeve gear when in 1st, 2nd or neutral.

Between the end of the selector dog splines and the sleeve gear were originally two thrust washers, one steel and one bronze 65-3098, 65-3104. These can be replaced with the mainshaft thrust washers from a Unit Single engine (C15 etc) as these are the same size in terms of diameters and are available in several thicknesses. The total thickness needed is found by comparing the complete mainshaft and gears with the layshaft. The total thrust washer thickness between the splines and sleeve gear should result in the space between the sleeve gear and the third gear being exactly the same as the space between the layshaft 1st and 2nd gears.
Do this job first before fitting the right thickness washer next to the kickstart rachet nut.

Between the sleeve gear and the bearing in the casing were originally two oil retaining washers 29-3858. fit a sealed bearing and replace these with one spacer washer of sufficient thickness to limit manshaft endfloat to the required 6 thou or so, from memory.

Diameters of the various shafts, gears and thrust washer are smaller than those fitted to the M series box so not much can be borrowed.
If original thrust washers were still available you'd stand a reasonable chance of it working when you fit them. Without all the
original washers in good condition it's a case of buying hardened washers of the right diameters and surface grinding them to the right thicknesses.
Not BSA's most user-friendly gearbox, this one.

[Rupert]

Small correction, 29-3858 originally fitted one either side of the bearing. Method described in previous post still applies.

[Greenfield]

Thanks Rupert. Just had a quick google for the parts nos and of course none are available.
I can remember rebuilding my B40 gearbox some years ago and playing around with these washers to get the endfloat. I have the specs of the B40 mainshaft washers, do you know the original specs of 65-3117? There are two of these in the B21 but mine are different thicknesses.
Cheers

[Rupert]

65-3117 is 0.1" thick. OD 1,1/16", ID just free on the shaft.

[Greenfield]

That's helpful. The two I have on the layshaft and mainshaft are thickness: 0.108 and 0.112", ID: 0.69" and OD: 0.175 and 0.18". As they're not undersize, when I can find some time, I'll reassemble the gearbox and concentrate on the 'inner' thrust washers.