Gearchange stuck on B52

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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magnusk750
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Gearchange stuck on B52

Post by magnusk750 »

I've had my B52 apart. Changed ball bearings and glands. Box generally speaking in good shape to my understanding, though I'm new to Burman boxes and I've never used it, belongs to my 55 G9 being built from parts.

Gears and shafts came together nicely, outer cover with it's gear change mechanism not so. I can turn the cam - barrel, feels like it moves quite freely, but I cant turn it with my fingers, need a screwdriver as a lever. Also the gear pedal shaft and fork attached to it moves quite fine, even if there is some play in the bushing. When assembled the gearchange will not move at all. I've tried to put the axle in the outer cover and attach the pedal and then mate it to the gearbox, and I've tried to put it onto the cam-barrel and then the attached the outer cover. Read somewere that it the position of the cam-barrel shuldn't matter. Is that true?

There's quite a lot of info on how to take the gearbox apart, much less on how to put it together. F W Neill writes only that assembly is reverse to taking apart.

All input welcome!
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Groily
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Re: Gearchange stuck on B52

Post by Groily »

I don't think you would normally be able to change gear on the barrel by hand - there's quite a lot of 'oomph' needed to get the selector forks moving in their tracks and the gear dogs etc engaging and disengaging, if you think about it.

The position of the barrel does matter, to the extent that the plunger has to be in the right indent for the gear the 'box is in, or for neutral. If you throw it together any old how you may get a couple of gears, but not the proper range. Many B52 owners, me included, will have got the T shirt on this the hard way over the years.

People do the re-assembly different ways I know, but I usually set the gear cluster to neutral using the selector rods, and fit the barrel with the plunger in the indent that is the 'neutral' one - ie the second indent from one 'end' of the arc of 5, with the smaller gap between it and its neighbours. The single indent to one side of the neutral indent is 1st gear, the three the other side are the other 3 gears. I think others maybe select a particular gear and follow the same general principle, ensuring the barrel cam is in the right spot for the one they've chosen.

If the thing is solid when the cover etc is fitted, it's usually owing to lack of end float on one or other shaft. Gasket thickness comes into play here - sometimes a thickish one solves the problem. It's another T shirt waiting to be awarded. If you slacken and then gradually retighten the outer cover screws, does it work until they're nearly tight? If so, that's almost certainly where the problem is.

I'm assuming that the contents of main- and lay-shafts are as intended by the makers (and the right way round!), and that bearings and bushes are fully home in their housings.
magnusk750
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Re: Gearchange stuck on B52

Post by magnusk750 »

Thanks Groily. I'll have to get out and check. Is there a figure on what endplay there should be in the shafts?
Groily
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Re: Gearchange stuck on B52

Post by Groily »

magnusk750 wrote: Sun Dec 19, 2021 8:06 am Is there a figure on what endplay there should be in the shafts?
Not that I know of, but someone better informed may be able to give a figure (and better advice too).
I'm just happy when everything works smoothly to be honest on mine. When set up right, with a well adjusted clutch, they are simply jewel-like in operation - absolutely silent into first even, which I never quite get with my AMC boxes.)

If you have any doubts about the state of the detent plunger and spring, by the way, replace it with new. Cheap and easy . . . they can cause missed gearchanges if worn I have found, especially at high rpm and under heavy load.
magnusk750
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Re: Gearchange stuck on B52

Post by magnusk750 »

Detent plunger is ok. Obviously I'll have to play more with positions of barrel and gear.
magnusk750
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Re: Gearchange stuck on B52

Post by magnusk750 »

Problem solved. O-ring on the outer shaft of the selector drum was too big, from the OC btw. Didn't seat properly, jammed the whole thing. Changed for a smaller one, will see if it starts weeping.
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ajscomboman
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Re: Gearchange stuck on B52

Post by ajscomboman »

magnusk750 wrote: Thu Jan 06, 2022 10:16 pm Problem solved. O-ring on the outer shaft of the selector drum was too big, from the OC btw. Didn't seat properly, jammed the whole thing. Changed for a smaller one, will see if it starts weeping.
You mean the rubber sleeve that fits under the indicator. Used plenty from the club and never had this at all ever! You don't seem to be having much luck.
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ajscomboman
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Re: Gearchange stuck on B52

Post by ajscomboman »

Just looked at your picture showing the selector, you do realise that the rubber seal doesn't fit where you have it. It fits on the shaft after the cover has been fitted.
magnusk750
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Re: Gearchange stuck on B52

Post by magnusk750 »

ajscomboman wrote: Fri Jan 07, 2022 9:21 am Just looked at your picture showing the selector, you do realise that the rubber seal doesn't fit where you have it. It fits on the shaft after the cover has been fitted.
Ajaj, Checking the exploded view again. No wonder there wasn't really room for the seal inside. A: My apologies to the owners club! B: bugger, I'll better remove that homebrewed o-ring I fitted, tried also without, and gearchange was smoother.
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ajscomboman
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Re: Gearchange stuck on B52

Post by ajscomboman »

magnusk750 wrote: Fri Jan 07, 2022 6:00 pm
ajscomboman wrote: Fri Jan 07, 2022 9:21 am Just looked at your picture showing the selector, you do realise that the rubber seal doesn't fit where you have it. It fits on the shaft after the cover has been fitted.
Ajaj, Checking the exploded view again. No wonder there wasn't really room for the seal inside. A: My apologies to the owners club! B: bugger, I'll better remove that homebrewed o-ring I fitted, tried also without, and gearchange was smoother.
Not a problem, I couldn't understand why you'd needed to fit the thinner ring till I saw the picture. :beer:
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