Gearbox sprockets

Started by phutton, February 07, 2022, 05:22:27 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.


Thank you everyone for your thoughts, and for the link to Tallon. You are quite right about 18T, they do need the front pillar reducing! Looks like 16 & 17 are the favourites, with 15 an option for SV, 350s and sidecar use.



Thanks David., for your offer of help.


That sounds like a really good plan. Let me know if I can help in due course!


My 9A turns out to have a 16T gearbox sprocket. 1st gear is very short, and it will pull away in 2nd. 3rd and 4th feel about right, and as the bike stomps up the local hills in the North Downs in 4th it would probably be fine with 17T. I've owned it for less than a month though and have only managed a couple of hundred miles so far, so I think I'll make a few more journeys before deciding whether to increase the gearing.


Sigarus - yes, it does seem to make sense to renew both sprockets at once, and chain life will definitely be extended. Let me know when you're sure how many teeth are needed..!


I'd be interested in a gearbox sprocket for a 1935 4-speed box (9A) although I haven't yet counted the number of teeth on the sprocket currently fitted. It seems as though it is most likely 17T but I'll check. I'm planning to replace the rear sprocket/drum so it makes sense to change the gearbox sprocket too along with the chain.


Funny you should post this - I've just been looking in my stash of parts this evening, and find I have about half a dozen 6-spline gearbox sprockets (and no bike that uses them!) Ranging from new old stock to utterly-knacked old stock.. I was going to post them for sale.
What i would add is that the first beam I restored, a Model 8, had a 15-tooth, which I stupidly had re-toothed at the same number. Great for towing steamrollers etc, but slow on the road - I soon changed it for a bigger one. I reckon any 500 - sans sidecar and on modern fuel - should pull 17. But 16 maybe good for 350s.
I THINK I once had one re-toothed at 18, which requires the clutch bridge stud to be cut away and is too long-legged really. Or I may just have dreamed this - it was all about 30 years ago!
Incidentally Talon Engineering in Yeovil specialise in making sprockets, and will grind off old teeth and weld on a new ring; but when I last had one done they did say that if they made a batch, it would work out cheaper per sprocket. Especially if the 'oil seal' spiral is left off, and replaced with a modern seal. Good people to talk to..


Hi Paul,
for me it will be rich two gearbox sprockets with 17 teeth (1923-1931).

In the last 10 years what I have seen are the most sprockets with 16 and 17 teeth.
I beleave for the OHV bikes will be 16 and 17 teeth, for the SV bikes 15 and 16 teeth.




We are looking at the re-manufacture of gearbox sprockets, and have found there to be just two basic designs - 1923-31 and 1932-34. The trouble is, each design has the possibility of five tooth numbers, from 14 to 18 teeth.

To cover everything from 1923 to 34 would mean we would have to stock 10 different sprockets which would be a very large investment, some of which would be in very slow moving stock. We then have to think about all those sprockets for 1935! I believe that, fortunately, the Burman items are catered for by the likes of Draganfly and other stockists.

I would very much appreciate members' thoughts on which ones we should go for.

Paul H