Grease Leaking From Burman gearchange Shafts

Matty

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VOC Member
Hi
This I know is an old problem which I have always had on long runs from the Burman gearbox on my Comet.
Had the bike 60 years and it always results in grease over the exhaust system.
Gearbox has been rebuilt several times with all the latest mods bearings and bearing seals and has no other leaks.
Have had some advice on another post which was primarily about another subject so have copied the relevant bits from the other post as below. Apologies if they are not attributed to the right people, my computer system has had a nervous breakdown and its brains are a bit scrambled :-

Apply the seals (o-rings) to the block, not the shafts.

clevtrev, Yesterday at 9:22 PM
#45
Thank You Reply




chankly boreVincent H.R.D. Owners Club Member

Grind a taper on the mouth of the gear shift hollow shaft, then install a very thin "O" ring to the selector shaft. It should leave a very small gap between the two shafts when assembled, or else too much tension will inhibit the action of the mechanism. The hollow shaft is very hard, so I find using a small grinding stone in a Dremel works best.
Click to expand...
Burman did make a step on the outer side of the selector shaft on early gearboxes and fitted a tiny felt ring. If you have this type you can fit a very skinny "O" ring. Otherwise, go with the accumulated wisdom above.

chankly bore, Today at 3:33 AM
#48
Thank You Reply


  • MattyVincent H.R.D. Owners Club Member
    Thanks for the replies about the leaking gear selector and change shafts. I was already using semi fluid grease, which is hopefully thixatropic grease by the way from Penrite.(ie. only liquid when agitated)
    I feel however that this is a bit of a diversion from the original problem of engine oil use so have started a new topic.
    I have not fully understood where to put the O rings or grooves on the gearbox outer case so will start another thread about the Burman leaks in a day or two with some pictures of gearbox parts.
    Matty

    Matty, Today at 10:09 AM
    #49
    Reply
  • Here is a photo of the burman gearchange bits and pieces with some writing on it which I hope will help me to understand what to do if anybody can explain please.
  • Sorry the jpg photo will not upload for some reason - it is about 500K large - is this too big.
  • Now reduced it to 125 K but it will still not go !!!
  • Basically I do not know where to put the Orings.
  • Do I grind a taper into the outer end of the hollow shaft bearing for an Oring on the shaft to fit into.
  • Or do I grind a taper into the inner end of the shaft bearing which the hollow shaft fits into with an Oring on the inner end of the shaft.
  • For the smaller inner shaft do I again grind a taper into the outer or inner end of the hollow shaft.
The picture would have made it much easier to explain.

Matty
 

chankly bore

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Non-VOC Member
Matty, go to page 11 of your Rider's Handbook. Where you need to relieve slightly for a thin "O" ring is the inside periphery of the F.C.L. bush, i.e. the r.h. side as illustrated. On early BAP gearboxes, the ratchet sleeve was machined for a felt seal at the splined (l.h.) end as well. A bit of searching at your local bearing shop will get you the THIN "O" rings you need. They can't be thick, otherwise they will stop the springboxes working. Philanthropic grease does help. Cheers mate.
 

Black Flash

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Just a thought. Make sure you have a small venting hole probably in the filler plug. Gearboxes get quite warm in use so venting is a must.
Merry Christmas to all of you
Bernie
 

chankly bore

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Just a thought. Make sure you have a small venting hole probably in the filler plug. Gearboxes get quite warm in use so venting is a must.
Merry Christmas to all of you
Bernie
Not necessary. Even if there was pressure built up, it would only force lubricant back along the clutch cable-a desirable and obviously well-designed feature! HO,HO,HO.
 

Matty

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VOC Member
Thanks
The above has made things much clearer and a thin O ring on the ratchet sleeve inner along with a small tapered relief for it in the inner end of the ECL bush to seat into may well do the trick.
I have always made sure that the vent hole in the filler plug was clear because even as a young apprentice 60 years ago I thought that pressure in the gearbox when hot could make the grease ooze out - but I was probably wrong about that even !!
However I still probably have some small leakage from the sector spindle.
Pity I shall have the messy, greasy job again which results when you remove the outer casing of the gearbox. Maybe I'll have a quick look after lunch on Christmas Day !!!

A few years ago some of us in the Club looked in detail on some nasty selector fork melt down problems with Burman boxes which were shown to be due to end float in shafts caused by a combination of production tolerances and wear.
I think the results of our investigation and some fixes, were published either on the forum or in the magazine around 2011 if anybody is interested.

I was a professional electronics circuit designer, Radar research Engineer and Defence Systems Salesman for many years, but always loved mechanics best, particularly cars and bikes - the work results in motion and noise.

Merry Christmas to All

Matty
 

chankly bore

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One reason for selector meltdown is the interference of the moving gear indicator with the travel of the footchange lever. Third and top gear are usually affected. Sometimes the output gear needs shimming immediately inside the output bearing as well. The original footchange lever was shaped such for a good reason.
 

Matty

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VOC Member
Thanks Yes I found out about the gear indicator contacting the gearlever and just holding the gear not properly quite into 4th many years ago. You have to move the gearlever round one spline to be sure.
Matty
 

Martyn Goodwin

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Hi Bernhard,

In the drawing it looks like there is a washer (its RED) that holds the "O: ring in place. Is that so? What is the dimentions of the washer?

Also do you suggest a second "O" ring on the outside between the case and the change lever?

thanks.
 
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Bernhard_Austria

Forum User
VOC Member
Hi MartinG,

The red washer is a standard hard gasket which was on stock in my workshop. It´s possible to replace it to metal one. Yes, it serves as a distance for the O-Ring, and it´s necessary due to the chamfered edge of the block. For the assembling process, the distance ring and the o-ring will be fitted on the shaft, so there is no damage from the spline.

I replaced the block to a new one because the hole was worn out.

I my gear change lever is a "pocket" on the inner side to the block. There was enough space for fitting a second O-Ring. But this one is only a protector against dust.

Bernhard
 
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