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G: Gearbox Burman lube questions...


brian gains

Well Known and Active Website User
VOC Member
The same spec' so I'm giving this a go with no ominous signs so far.
1579902798593.png
 
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Bill Thomas

Well Known and Active Website User
VOC Member
A while ago I striped out a box that had been sitting for 20 years plus, Could not change gears,
It was just the old grease turned solid !.
 

vibrac

Well Known and Active Website User
VOC Member
And I had a Douglas gearbox that would not work because the grease was packed in to tightly (it now has Penrite in it)
 

Colin

Well Known and Active Website User
VOC Member
Oh Tim!
One of the great pleasures of the Comet is brewing your own lube and slurping it in
To quote, or strictly, requote, MPH 381 "But Comets,ah, Comets are Heavenly"
 

vibrac

Well Known and Active Website User
VOC Member
Oh Tim!
One of the great pleasures of the Comet is brewing your own lube and slurping it in
To quote, or strictly, requote, MPH 381 "But Comets,ah, Comets are Heavenly"
I think I can forgo that pleasure along with cooking linklife for rear chains and plasticene baths for cable lubrication:D
 

erik

Well Known and Active Website User
VOC Member
The Landrover product contails everything to withstand high pressure.I believe that in the defender axle there is more torque and pressure than in any burman box.Since mor than 10000 miles no problem.Regards Erik
 

Marcus Bowden

Well Known and Active Website User
VOC Member
Mobil SHC (132?) fully synthetic, about 25 or more years ago the company introduced synthetic oils, Starting Air compressors use to give big troubles with carboned up v/v plates & Rarus synthetic stopped it completely, the wear on Westfailure crown wheels & pinions was regularly changed every six months, when changing to Mobil SHC they lasted 2 years plus. But if I leave the "A" running on its side stand it tends to drip out constantly, stripped too many Burman's with dried out grease around the edges, 'tis a wonder they lasted so long.
 
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Matty

Well Known and Active Website User
VOC Member
I once had the "screech " problem some years ago when I used ordinary LM grease in my Burman and was in the Isle of Man for the Manx.
I added a small amount of engine oil which fixed it straight away.
However I have since used PENRITE which I buy on line from Classic oils at about half the price the Voc spares charge !!!
Matty
 

druridge

Well Known and Active Website User
VOC Member
On a previous thread I mentioned dismantling a Burman B52 box (actually on an AJS scrambler but nearly the same), filled with 50/50 gear oil (eg 90 grade) and grease. After years of running, nearly all the grease was found flung out into the outer reaches of the gearbox casing, with the gears happily immersed in the oil somewhere in the middle. In this case , at normal operating temperatures I dont think the grease melted.
I cant see how leaving any grease in these remote corners can do any harm; it does require you to refill/ top up the oil to the correct level though, rather than just measuring out the correct amount and tipping it in.
 

Matty

Well Known and Active Website User
VOC Member
Hi
This is probably too much information but is a summery of our findings from work done some years ago.
My box has now done many thousands of miles since this rebuild with no problems at all.
The only work carried out since was a pretty successful attempt to stop the leak from the gearchange shaft by adding some O rings and doing a little work on the bearing using some information and drawings from a member from I think from Austria.
This information is on the forum somewhere and I will try to find it but have the drawings of the modification which I will copy and attach to this when I have the time.

Series C Comet Burman Gearbox Rebuild



Way back in 1957, just after having bought the Comet in 1956, the gearbox destroyed itself when a tooth broke off one of the mainshaft gears. This bent the mainshaft, layshaft and severely damaged the casing when it got between the teeth.



I was a poor 21 year old apprentice so had to buy a new mainshaft sliding gear, but straightened the bent mainshaft as best I could on a flypress and persuaded the welder at work to patch up the cracked gearbox casing.



This has lasted until 2 years ago, when 3rd gear gradually became more noisy and grease began to leak onto the chain in unacceptable quantities. I changed both 3rd gears and the layshaft – which I found was also bent and replaced the seal for the sprocket output shaft. After a 1200 mile trip to the Manx Grand Prix, the grease still leaked out over the chain and 3rd gear was no quieter.



I decided that at the end of 2011 I would try to finally fix the gearbox, 55years and 60,000miles or so after the “explosion”.



I looked on the forum to try to find a new casing, because mine was cracked near the output bearing and the flange casting inside the bearing housing had been largely broken away during the 1957 “explosion”. Whilst looking on the forum for a replacement box, I found that two other members had had a serious problem recently, when the top-gear bronze selector fork had welded itself to the sliding gear and broken up.



The question was why this had happened and I felt I would like to know the answer before I rebuilt my box, to ensure that I did not have the same problem. So began a 7 page thread to investigate what was called “The 4th Gear Meltdown”. This debate involved Vic Youle and Tatty500 who had had the problem and several others including Clevtrev, all of whom made valuable contributions to the discussion.



Vic’s broken parts were passed around using long and complicated routes and it could be seen that the dogs into 4th gear were tapered and only engaging by about 1mm – this would have put much pressure on the bronze selector in that gear, causing it to overheat and weld itself to the sliding gear – despite both gearboxes being filled with the correct lubricants.



Clevtrev found me a good gearbox casing and fitted new bronze bearings. With a new output bearing and seals fitted to the gearbox, my 4th gear’s dogs engaged about 3.3mm with all the parts – shafts, selectors, gears etc moved into the worst case direction. Vic’s old parts including selectors gave a similar reading which should not have caused him problem. So the missing 2mm or so was probably due to differences in his and my casings.



However to make sure I would not have a problem, I have put some shims of about 1mm total thickness between the main driving gear output and the inner of the bearing, which gives the dogs 1mm more engagement. NOTE the output gear had about 2mm of clearance from the bronze selector in 4th gear and I have “stolen” 1mm of this. It is very important that the shims - 1.5” internal diameter, must be not greater than 44mm outside diameter, to ensure that they will not foul the inner diameter of the aluminium flange behind the output bearing. Check that they do not foul after putting the chain sprocket on very tight and before assembling the rest of the gearbox, mine just scraped and a bit more had to be taken off the outside diameter of the shims.



I believe that my 4th gear dogs now engage by around 4mm, even though I had never had a problem with mine.



Another reason that the gear dogs might not properly engage can be end float on the selector shaft and wear on the selector pins. On my gearbox there is only a few thou wear on the pins, so I have not renewed them. However when I put the end casing on the gearbox, WITH THE PAPER GASKET which acts as a spacer to give suitable end float for the layshaft, I found more than 1mm end float on the selector shaft. So I removed the steel bush which the rollers fit into and put it back with a suitable shim behind it, making sure that there was still about 10thou float left when assembled.



To add to the above, it has been pointed out, that in the past the bronze bush on the output gear which the mainshaft runs in sometimes works loose and moves inwards. This then prevents the 4th gear dog on the sliding gear from fully engaging and hence can cause wear on the dogs, excessive friction on the bronze selector and ultimately meltdown. Unfortunately this information came a year too late for me to check this on my gearbox, but it seems OK, so I hope I do not have this problem.



The other change I have made has been to the output bearing which the chain-sprocket gear runs in.

This bearing is a very strange size by the way, 72mm outside, 1.5” inside diameter and 17mm wide and I obtained mine from Peter Barker Engineers. It was sealed on both sides and I have left the seals in – sealed bearings seem to work for years in Alternators on cars, so I think they should be OK and will doubly ensure no grease leaks from the gearbox



This bearing should be shrunk into the casing (at 150/200degC) down to the flange and was originally held in with an oil seal, a spacer which looked like a piston ring, some crinkley washers and then a large circlip.



This arrangement has worked well and is fine if the “crinkley washers” keep pressure on the bearing and oil seal, otherwise the output gear could move out and reduce the 4th gear dog engagement.



However there is a new and better part (BA 1948-52) obtainable from Draganfly which is a spacer with an oilseal in it which replaces the old oil seal and “piston ring” spacer. The inner of the new oilseal still runs on the sprocket spacing collar between the chain sprocket and bearing. The oilseal spacer has the same outer diameter as the outer of the bearing and is held in by the large circlip, possibly using a crinkley washer or two to take up any slack if necessary.



I put a little Locktight round the spacer to make sure that grease can not get by it.



My rebuilt gearbox has now been running with no problems for about 5000miles and for some reason I do not understand, even the whining 3rd gear is much quieter with the same thixotropic (gel when stationary – liquid when agitated) grease as it has always had.



I hope that Tatty500 and VicYoule have had similar success with their Burman rebuilds following our lengthy discussions on the forum.



My only remaining gearbox problem is that even when filled with thixotropic grease, there is still a small leak of grease from the gear lever bearing on long runs. It has done this to me for nearly 60 years, so I suppose I will have to get used to it, even though I have blocked the two holes between the inner and outer casings.



I’m also hoping that the gearbox mainshaft I straightened by eye on a flypress all those years ago will be OK for another 50 years.or so !!!



Matty



Since writing this in 2011 third gear became very noisy in July 2015 and when I stripped the gearbox I found that the bronze bush that had been fitted had seized onto the layshaft and turned in the casing which was quite badly damaged.



I took the casing to Bob MacDonald in Maldon and using the counterbore where a core plug is fitted to seal the bronze bush as a guide, he bored out a new larger hole for the bearing and made a new one from iolite. I think perhaps the bronze used may not have been suitable as a replacement for the original Burman iolite one.

Also replaced the bush at the other end of the layshaft.with an iolite one.

I rebuilt the gearbox again with another layshaft (second hand from Draganfly) because the bearing on it had also been damaged and was now undersized though possible regrindable if things were desparate.



Filled box with 800 grams of Penrite semi fluid grease from Classic oils which is specially formulated for Burman boxes. It may be best to do this before putting the bits into the gearbox, but mine has a grease nipple on top which enables me to fill it from a grease gun after it is in the bike.

If the gearbox leaks a little grease from the gear lever bearings, which mine has always done, it is impossible to know how much is left in – I just dip when it is warm through the filler hole and believe around 1.25 inches of grease is probably about right.



3rd Gear now pretty quiet after around 15,000miles.
 

Matty

Well Known and Active Website User
VOC Member
Hi
Think I had a computer brainstorm and had no included the drawing of the bearing modification and picture of the inside of the gearchange area with the bearing.
Hope the pictures are OK but I had some problems composing the reply.
Matty
 

Attachments

Matty

Well Known and Active Website User
VOC Member
Another fix was to seal the bearing and spacer from DRAGANFLY suggested by BOB Macdonld which was to turn a fine groove in the outer of the oilseal/spacer ( around 1mm wide) and put in a large diameter O ring as an additional seal to the bearing casing.
This is probably belt and braces but seems to have helped.
Matty
 

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