Burman B52 conundrum

[enigmas]

Hi I'm new to the forum and have signed up to try and get some clarification on a Burman B52 gearbox I was sorting out with a friend. The bike, a 500 twin, swingarm, rear jampot suspended AJS is a partial bitsa that has been seemingly reliable for the last couple of years that I'm aware off. The problem is that recently it has had difficulty selecting 3rd & 4th gear. It's not the clutch.

We removed the box and disassembled it finding that both selector forks were bent and blued. Neither of them turned freely in their engagement slots on the dog clutches. I straightened the forks with my oxy/acetylene set and linished the fork fingers. So both now operate smoothly.

Once reassembled' the box changed through all the gears on the bench satisfactorily. We then refitted it to the bike. Upon riding it 1st & 2nd gear went in readily but 3rd & 4th seemed absent unless the gearstick was given a second push down after a pause.

These are my queries: There's a large U shaped leaf spring fitted to the box behind the gearstick cover. Part no. 36-11-1.


1. Do the open ends of the leaf spring fit over the fork that rotates the gear quadrant selector spool?
2. Is its purpose to centralise this fork and return the gearstick mechanism to its central 'at rest' position?

The ends of this leaf spring appear to be opened up/stretched open too far to provide any sort of viable function.

Any assistance and/or clarification on this matter would be most welcomed.

~ Vince (in Oz)

[SPRIDDLER]

Welcome, Vince.
This may help you.

http://archives.jampot.dk/technical/Tra ... ebuild.pdf

[enigmas]

Ok, scratch my query/reply below. I just checked an exploded diagram and the light spring (3746-52) is fitted correctly between the selector fork and the inner face of the outer case.


Thanks for that PDF Spriddler...the pictures help considerably in seeing where the components fit. Now I don't believe that the leaf return spring was incorrectly fitted as we didn't remove it from its place in the outer cover.

With reference to the 7th image 'VIEW ON THE INSIDE OF THE OUTER KICKSTART CASE' one of the text box indicates with an arrow the location of the gear selector drum coil spring 3746-52.

Does this light spring fit between the selector fork and the face of the outer case or on top of the fork where the small dowel locates in a hole drilled in the inside of the main case.

~ Vince

[enigmas]

I think we now know what caused the bent/blued selector forks and the original gear selection issues. Apparently the box original symptoms were difficulty engaging 3rd and 4th gear sometimes and then refusing to stay in 4th.

From my reading of tech literature about the B52 box, this seems to indicate a well worn mainshaft bearing behind the sprocket. Could someone chime in and verify if this is the correct conclusion.

One further question, can this bearing be removed and replaced with the gearbox in situ, but with the complete primary drive side/clutch basket removed?

[1608]

Hi Vince, I've just re-built a Burman GB box, I think they are the same in principle. If Spriddlers pics are of a b52 then both boxes are very similar.
To answer your question, yes the spring is to return the selector quadrant to the central position. And fits exactly as in the pics.
False neutrals and difficult gear selection and the dropping out of gear ( normally 3rd) is sometimes caused by either wear in the selector drum, but usually the two dowels that fit into the end of the forks. Also, if there is too much end float on the selector drum when the outer cover is fitted. Without wishing to go into egg sucking mode, sloppy problems with gear boxes is an accumulation of many parts that are a bit worn culminating in an aggregated problem. Sum of the parts and all that!
Having re-read your post, the 'u' spring you mention should be strong enough for the two ends to be stretched over and located on the pegs moulded on the inside of the outer case. The gear change selector fork that works within this spring acts on and rides over the pegs on the selector drum/cam. That selector is pressed in place by a spring btn it and the outer cover. Being new to this site have you searched the menu yet and found the 'Tech articles' at the top of the page. See under gear boxes, b52 is the last item under gear boxes. Good luck.

[enigmas]

Thanks for reviewing my initial question again 1608, but as I'm not a paid up member just a guest on the Forum, those files aren't accessible to me and are locked off!

Inerestingly, I've posted several other queries trying to clarify this issue, but these don't appear on this Board or topic either?

I don't believe there's a stack-up of clearances causing the poor lack of engagement in 3rd & 4th...and the return springs are fitted in the correct place now that you've clarified it.

If the mainshaft bearing at the sprocket end is worn would that under load cause either difficulty in engaging 3rd & 4th or cause 4th to disengage? (the dog clutches to move out of mesh)

[Groily]

Having just recently broken the selector return spring on one of mine, replaced it, and had some similar difficulties (in my case, 3rd to 2nd and second to neutral sometimes needing the 'second prod'), the only thing that I could add over the 'sum of the parts' point made already, is to check the gear indicator shaft isn't binding due to incorrect assembly of washers etc. If this shaft is sticky in the outer cover, it can also hinder operation.
But the main issues are the state of the blade spring, the state of the barrel cam and the selector rod pins that engage in it, and the endfloat. It really is a question of several things sometimes.
I seem to recall once having to use a thicker outer cover gasket material to get a few more thou clearance, which transformed matters. I have also had, once, a problem with the tails of a split pin on one of the selectors getting out of shape and fouling (which taught me to make sure the tails were trimmed to the correct length!).

[robcurrie]

Non-members will not have access to the technical section.

Rob C

[1608]

Vince, the tech article I was refering to covers the point of jumping out of gear. This is sometimes caused by the gear not selecting fully. This can be caused by wear in the cam/drum but also more commonly with the dowels that are fitted in the end of the fork spindles and too much end float on the selector cam/drum. This can be aggravated by a too thicker outer gasket . Dropping out of gear can be caused by
badly worn plunger that locates in the dimples on the rear of the drum or a broken plunger spring. The dogs will want to separate under load if they are badly worn that is why the previously mentioned worn parts add to the problem. I don't think wear in the main bearing would cause these problems. Is the main bearing badly worn. If the shaft can wobble that is just as likely to be the sleeve bushes. I was told by a gear box know-all that the accumulation of worn parts adds up. So just replacing one suspected part is a false economy I'm afraid. Its worth replacing the main suspects whilst the box is apart. When the outer casing is fitted how much end float is there (with the indicator disc is removed ) try pushing it in.

[enigmas]

Hi Rob, I'm just trying to repair a gearbox for a friend...not trying to steal anything!

Thanks again Grolly and 1608. We had most of the gearbox apart but didn't remove the gearbox sprocket as that looked and felt ok, but perhaps I didn't look hard enough. All the rotary selector mechanism looked fine but what didn't, were the 2 bent and blued selector forks that moved the dog clutches. Seeing these, I presumed that these were the primary cause of the faulty operation.

I like to run the bike on a stand with the back wheel in the air so there's no 'real' torque loading on the mainshaft sprocket and see if it selects 3rd and 4th more easily. After that test refocus on wear in the selector mechanism.

We refitted the the outer cover using anerobic sealant so there is no gasket. The original was very thin and I did read some tech literature stating to leave it out to reduce tolerances on the gearchange mechanism. The box does select 1st and 2nd fine.

Perhaps the indicator mechanism is binding (nut too tight or not enough clearance when tightened, but I doubt it as 1st and 2nd are fine.)

It worked fine on the bench so I 'd say the issue has to do with torque loading.

As 3rd and 4th are the most used gears I'd like to revisit that particular dog clutch as I did notice the tapers on the engagement segments of the dog were rounded.

I also read that reducing the distance this dog clutch moves by placing a thin spacer behind one of the gears can cure the engagement issue on 4th.

Any observations on these considerations?