gearbox parts

I have bought a gearbox in bits with a bag of miscelaneous gears. Does anybody know if the later models had a physically larger 4th gear (sleeve gear)? The one I have has the correct number of teeth but appears to have a larger outside diameter when compared with one I took out of another standard 750 gearbox.

Dave

What are the sizes?

The fourth gear pair changed around 1971-on I think?

The earlier gear set being parts 04-0422 M/S and 04-0284 L/S
The later set being 06-1057 M/S and 06-1058 L/S

Service Release N61 Sept. 71 informed dealers that whenever the earlier part numbers were ordered then the later parts would be supplied and that it was vitally important that both new parts should be used together.

Thanks L.A.B., The gear in question is about 65.7mm diameter across the teeth as opposed to 64mm which is the size of the gear taken from a circa 1970 gearbox, presumably the matching layshaft cog (missing in this case) is correspondingly smaller. The good news is that I got the box on e-bay for a little over U.S.$100 and the rest of it is in good shape.
I suppose after I replace the sleeve gear I will have a spare one which could form the basis of a new project!
Dave

dave M said:

The gear in question is about 65.7mm diameter across the teeth as opposed to 64mm which is the size of the gear taken from a circa 1970 gearbox,

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I just measured up a late (MkIII) one and that is 64.50mm!! The layshaft gear being 52.28mm.

Addition

The 18/23 tooth 4th gear set was used from 1960-on so I thought that possibly the 65.7mm one could be a Dominator part? But even the early sleeve gear has the 04-0422 part number??

L.A.B., I remeasured with a vernier and the size varies from around 64 to 64.5 depending on the gear-teeth position within the caliper jaws, so we are basically in agreement on the standard size.

I note that in the Andover Norton spares catalogue they list the MK3 sleeve gear as pt# 06-5954

from your own measurements of the MK3 gear It looks like this corresponds with my earlier parts size and that this is the most common size, consequently I will get a standard gear set and I should be on my way.

Many thanks for your help.
Dave

dave M said:

I note that in the Andover Norton spares catalogue they list the MK3 sleeve gear as pt# 06-5954

Click to expand...

Yes the 850 MkIII sleeve gear does have the different part number, that's because it has an internal circlip groove, (the circlip acts as a sleeve gear bush retainer -maybe I should have mentioned that?) however the Mk III layshaft gear is the same part as the previous one (06-1058) so there's no actual dimensional difference to the MkIII sleeve gear itself as far as I am aware.

All has been revealed! I just checked the 4th gear sleeve-gear from my chum's Triton with a Dominator gearbox and the dimensions are the same as the one I have ie 65.7mm, also the layshaft 4th gear is 50.7 mm so it looks like the gears were changed before or for the launch of the Commando.
Dave

dave M said:

All has been revealed! I just checked the 4th gear sleeve-gear from my chum's Triton with a Dominator gearbox and the dimensions are the same as the one I have ie 65.7mm, also the layshaft 4th gear is 50.7 mm so it looks like the gears were changed before or for the launch of the Commando.
Dave

Click to expand...

Roy Bacon does mention (in his 'Norton Twin Restoration' book) that the 1968 Commando "....had a revised sleeve- gear and first gear-gear pairs plus an amended layshaft second gear...."

Although there does not appear to be any change to the sleeve (or layshaft) gear part number until two years later!!

Roy Bacon also says that the bush retaining circlip sleeve gear was fitted from 1974 and the sleeve gear was modified again for 1975, although that doesn't appear to tally with the BSA Regal (Andover Norton) parts list (unless it was introduced at some point during the 1974 production run?) The later 065954 now being the recommended replacement part.
The sleeve gear I checked (stamped 'AH') only appears to have only one circlip and groove (at the outer end), so possibly this part is the intermediate one or the earlier (longer) plain bushes are fitted covering the inner groove (and there's no way I can see unless I were to remove the bushes)?
As the MkIII parts diagram shows two circlips and the MkIII bushes (three fitted) are shorter?