Burman gearbox GB52 problem

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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David1977
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Burman gearbox GB52 problem

Post by David1977 »

Hello, I have G9 almost for 5 years. I have problem with the gearbox from the begining . I can not shift from 4th down to 3th gear without problem. I am not sure where should I look at and how to solve this ? Last year I removed outer and inner cover for gear inspection and found out that gear sprocket 21th has broken one tooth so I managed to get new old stock so I put all together but shifting from 4th down to 3th hasn't changed .
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Groily
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Re: Burman gearbox GB52 problem

Post by Groily »

As no-one has come back on this, here are a couple of thoughts . . .

You don't tell us whether the problem getting from 4th to 3rd was 'a nasty crunching noise' or a 'won't change gear at all' thing, so there could be several things.
We must assume that the main and layshafts are correctly assembled and straight, with all the right bits in all the right places, according to the book?
And that the shafts turn freely in the gearbox when it is in neutral.

There are two particular areas I would look at. First, check that the selector rods and forks are not bent, that the 'pegs' that engage in the barrel cam are free to slide around their grooves and that the grooves themselves are not damaged.
Then I would look at the rear of the barrel cam and the state of the 'detent' plunger that sits in the 5 holes on the rear face. Wear there can make it hard to find gears sometimes (but shouldn't cause graunching noises in my experience, rather a refusal to change gear). New plungers and springs are available - but beware the fact that some of them (all of them even?) may be a bit too 'pointy' on the end to allow smooth selection and may need rounding off to get a smooth fit. (Don't ask me how I know - I have just been there with one of mine!) Check also that the bushings are 'ok' on the inner and outer ends that support the cam.

I would also look at the gear selector return spring blade. A worn one can cause the non-return of the lever to the central position for finding the next gear. That is usually evident if you CAN change gear after just touching the gear change lever in the opposite direction to the one you want to go next. Ie touch it on the upper side before a downchange or the underside before an up-change.

Others know these things far better than me, but unless you actually have a bent mainshaft or layshaft,, I can't see what else might be causing the problem.
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David1977
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Re: Burman gearbox GB52 problem

Post by David1977 »

Thank you for explanation. Sorry I did not mention that There is a crunching noise when I switch from 4th to 3th . I will split up the gearbox for inspection and I will come back If I need advise.
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ajscomboman
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Re: Burman gearbox GB52 problem

Post by ajscomboman »

There are few possible issues but as I'm just about to leave for the jampot Rally I don't have time to go through them. If it can wait till I return on Tuesday I'll try to post pictures of the different thickness gears etc, mainly located around the sleeve gear and corresponding cogs.
SPRIDDLER
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Re: Burman gearbox GB52 problem

Post by SPRIDDLER »

David1977 wrote: Thu Aug 18, 2022 9:42 am I will split up the gearbox for inspection and I will come back If I need advise.
Welcome to the club, David.
Several engineering and exploded diagrams and articles on stripping and refurbishing the B52 gearbox in the Archives.
See here:
http://archives.jampot.dk/technical/Tra ... on/Burman/
'There is a tide in the affairs of men
Which taken at the flood............'
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David1977
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Re: Burman gearbox GB52 problem

Post by David1977 »

Hello guys. Today I opened the gearbox for inspection I did not find brouken tooth of any gear . But there is a litle play on innternal gearing and I am not sure If it could cause crunching noise when I change from 4 up to 3 gear . Is there any chance to get new gears ? I coul not find any available .[img]
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