B52 gear box problem

[JDFS79]

Hello everyone ! I'm having a problem with my gear box(g3ls 1952) , when in 4 gear "on the road" it jumps and engages again over and over!!!! Before i hit the road i have made a test in the garage with the rear wheel off the ground and it was ok (beside a neutral between 3 and4, and not always) i achieved full throttle in 4. But with some load the problem appeared.. What could it be? All the others gears work good.

[Andy51]

Assuming the gear teeth are in good condition, the main cause of jumping out of gear is the spring-loaded plunger (G-42-1) underneath the cam assembly (018337) in the outer case. If this is worn or sticking gears can jump out of engagement. The good news is that you can get at this by removing the outer cover (tie the kickstart to the gear lever with wire to stop the spring unwinding); the cam lifts out to reveal the plunger. Check for wear (the nose should be fairly pointed, not worn down to a rounded shape) and free movement, then reassemble. Spare plunger and springs are, I believe, available. Hope this helps, Andy

[JDFS79]

Thanks Andy, but i believe that is not the problem the plunger and spring are new and the gears where ok .
When it jumps the gear lever doesn't move, but the kickstart lever yes ....

[oldandsmelly]

Hi, I don't know if you've solved this yet but I thought I might add a comment and suggestion to try and help.

I've rebuilt B52's a number of times and they are very simple and basic boxes which, in my opinion, is a good thing as there is less to go wrong. If the box is jumping out of 4th only, one possible cause is that the 2 bushes on the high gear are badly worn which allows the high gear to slop around a little on the mainshaft which has the effect of the bike wriggling out of 4th under load. Normally, if this wear is there, oil will tend to leak by the 2 bushes when the bike is on the side stand and appear to be coming from the gearbox sprocket end although this probably isn't a guaranteed test. The good news if this is the fault is that these bushes are aavailable and easy to fit although you will need some hand reamers to get a good fit finish.

As has been mention above, the other possible cause is the selection mechanism . Other than the selection pawl and spring wear or the failure mentioned above causing selection problems, the V-shaped plate that registers on the selection drum can wear on the 2 "ears" that do the actual turning of the selection drum. Also, the spring behind this V plate can weaken and fail which means that the selector drum doesn't get turned fully to its next position leaving it likely to leap out of gear. Having said all this, selector faults tend to affect interemediate gears as well and not just 4th. To test the selector bits, you could select 4th gear and then take the outer gearbox cover off and see if the selector drum is where it should be.

hope this helps - good luck!

[JDFS79]

Thanks i will change the bushes, that's the problem for sure, Now i will need courage to took the box apart again...

[56G80S]

I used an old tea chest as a small spray booth and even rigged an old vacuum cleaner to suck away from the open end; not sure thyat was a good Idea but I thought so at the time (25 years ago).

Johnny B

[JDFS79]

I have order the bushes today from the club spares. So next week i will start the job. Where can i find some good hand reamers for this job?

[oldandsmelly]

I think I bought my hand reamer set from Axminster tools which are on the net.

Taking the gearbox apart for the first time can be daunting, but the good news with B52's is that you cannot reassemble them wrong as everything only goes back one way. There's also no stress about indexing gears as the selector drum and forks arrangement is sort of self indexing in that you don't need to line up indents and pawls etc like on some boxes.

If any of the intermediate gear bushes are worn, these are also very easy to replace. I bought mine from Draganfly as I don't think the club stocks them. One tip for an easy life when replacing the bushes is to get hold of some freezer spray meant for plumbing work ( I get mine from B&Q) and to spray freeze the new bushes to shrink them slightly just before you push them in. I've never found them difficult to get in, just tap them home gently then ream to fit the shaft. I've only ever found a light reaming is necessary for a good sliding fit so it shouldn't be a long job.

[JDFS79]

When i recently change the main drive bearing i should have paid some attention to the bushes, i notice that they were not as a work shop said they should be ( with a free space between them ) and mine were close together with some free space to the gear box sprocket ... Now i will learn the hard way ... Do it all over again i think i can do it with the box in situ !! Or am i wrong?

[oldandsmelly]

I have pondered why the gap between the 2 bushes on the high gear. I've assumed it's to hold a reservoir of oil because maybe if it was one long bush, insufficient oil would get to the sprocket end? For info, I always tap the sprocket end bush in so that it's flush with the end of the high gear.

You can do the work with the gearbox shell still in place but you need of course to remove the primary drive bits to be able to remove the gearbox sprocket. Removing the large gearbox sprocket nut can be troublesome sometimes, the quickest and least stressful way I've found is to use an impact gun just to give it that initial loosen.

When you remove the high gear, it's worth checking the internal teeth on the end which engages with the second sliding gear that slots into it. Don't worry if the high gear and second gear seem to rattle together loosely when you put them together but check if the external engaging teeth dogs on the two gears are not badly worn away from the squarish profile they would have been when new. If they are, this certainly helps the bike leap out of gear when under load especially when combined with worn bushes. Some rounding of these dog teeth are to be expected with bikes of this age but it should be clear if they are badly worn - they will taper from square to round profile from inside to out.

As far as I know, Burman gears aren't available new anymore. If you do find that your high gear or second sliding gear are too far gone don't despair; I have these gears in my 'come in handy' stash in my shed and can let you have them if things get desperate.