I have just had a look at my mainshaft sliding gear and it seems to be only engaging 2 mm. This on a BAP M26 Feb 1952. I don't know how to post photos but if you email me at donharvey@dcsi.net.au i will send photos or whatever measurments may be useful. I am clearly reluctant to put it together as it is. Kind Regards Don
Burman 4th Gear Selector Meltdown
- Thread starter tatty500
- Start date
Hi
Mine was better than this at about 3mm, but I put a 1mm hard shim spacer washer behind the output gear to move it in a little. 1mm still allows about 1mm clearance from the bronze selector or layshaft gear.
This was quite a narrow spacer washer (only about 3mm), because otherwise it will scrape on the inside of the aluminium flange behind the beariing if the spacer has too great an outside diameter.
I also removed as much end float on the selector shaft as possible, by moving the shaft roller bearing at the gearchange end in to take up any end play. You could put a suitable spacer behind the selector shaft roller bearing flange for this, but my bearing was very tight even after heating and I just moved it in a few thou to avoid damage bashing it.
My gearbox now works very well and I have done about 500 miles with it since Christmas.
Good Luck
Matty
Mine was better than this at about 3mm, but I put a 1mm hard shim spacer washer behind the output gear to move it in a little. 1mm still allows about 1mm clearance from the bronze selector or layshaft gear.
This was quite a narrow spacer washer (only about 3mm), because otherwise it will scrape on the inside of the aluminium flange behind the beariing if the spacer has too great an outside diameter.
I also removed as much end float on the selector shaft as possible, by moving the shaft roller bearing at the gearchange end in to take up any end play. You could put a suitable spacer behind the selector shaft roller bearing flange for this, but my bearing was very tight even after heating and I just moved it in a few thou to avoid damage bashing it.
My gearbox now works very well and I have done about 500 miles with it since Christmas.
Good Luck
Matty
Dear Longdon
Matty has said just what I would have, except that there is another cure for the recessed wear on the thrust face of the selector roller sleeve. The wear ridge can be milled off and then a washer made to get back to having hust a few thou of end float.
Also do check the face of the selector for wear, but you've probably already done that.
I still haven't put my box together but now that the cracks in kick start stop peg boss are welded, it only needs the weather to warm up a bit.......honest!
I'll also mail direct.
Tatty
Matty has said just what I would have, except that there is another cure for the recessed wear on the thrust face of the selector roller sleeve. The wear ridge can be milled off and then a washer made to get back to having hust a few thou of end float.
Also do check the face of the selector for wear, but you've probably already done that.
I still haven't put my box together but now that the cracks in kick start stop peg boss are welded, it only needs the weather to warm up a bit.......honest!
I'll also mail direct.
Tatty
Thanks Matty I had someone look at it today and he pointed out that it has had repair work around the clutch end of the main shaft where the clutch had been loose at some time, had the mainshaft bearing replaced at least once, and some evidence the driving gear nut has been loose. He thought that the wear marks on the driving gear maybe due to one or all of these and i shouldnt panic till we have assembled it as VINCE998 suggests, with new bushes, and care to establish how far it engages now. Might take a week or so as i'm a bit busy just at the moment. Will keep you informed.
Regards Longdon
Regards Longdon
Hi
About 5 years ago I found that my clutch was loose on the mainshaft gearbox splines. The gearbox splines were fortunately perfectly OK, but the "clutch centre" (PR50 2x ?) splines/dogs were very worn due to a little slackness having developed in the big fixing nut holding the clutch to the mainshaft. So little was left of these dogs in fact, that they would probably have soon sheared off and all drive would have been lost
I had to buy a new clutch centre (from Conway Motors) for around £80 to fit properly onto the mainshaft and have since done the nut up as tight as I dare onto its tabwasher to prevent this happening again.
With all due respect to Burman, I feel that the design of this is not really very good, because the full torque of the engine power (or overrun) multiplied by the ratio of the primary drive is being applied to loosen the centre nut. However it can't be too bad because mine had given no real trouble for 60 years !!
If you look back through this long saga you will see that I have replaced my mainshaft bearings with sealed ones (have kept the seals in both sides) from barkers@engrs.wanadoo.co.uk because the large bearing at the drive end is a very unusual size (72mm outside and 1.500" inside diameter by 17mm wide)
I also used a modified spacer, oil seal and oil seal housing assembly from Draganfly -( BA 1948-52) behind the output bearing circlip and bearing which seems a much better arrangement than the original one.
Hope this may be of help to somebody.
Matty
About 5 years ago I found that my clutch was loose on the mainshaft gearbox splines. The gearbox splines were fortunately perfectly OK, but the "clutch centre" (PR50 2x ?) splines/dogs were very worn due to a little slackness having developed in the big fixing nut holding the clutch to the mainshaft. So little was left of these dogs in fact, that they would probably have soon sheared off and all drive would have been lost
I had to buy a new clutch centre (from Conway Motors) for around £80 to fit properly onto the mainshaft and have since done the nut up as tight as I dare onto its tabwasher to prevent this happening again.
With all due respect to Burman, I feel that the design of this is not really very good, because the full torque of the engine power (or overrun) multiplied by the ratio of the primary drive is being applied to loosen the centre nut. However it can't be too bad because mine had given no real trouble for 60 years !!
If you look back through this long saga you will see that I have replaced my mainshaft bearings with sealed ones (have kept the seals in both sides) from barkers@engrs.wanadoo.co.uk because the large bearing at the drive end is a very unusual size (72mm outside and 1.500" inside diameter by 17mm wide)
I also used a modified spacer, oil seal and oil seal housing assembly from Draganfly -( BA 1948-52) behind the output bearing circlip and bearing which seems a much better arrangement than the original one.
Hope this may be of help to somebody.
Matty
Hi Matty.
Thanks Matty Someone has done a pretty fair job of repairing the gearbox splines and clutch centre splines on mine but the distance between the output bearing circlip and the bearingis about 3.6 mm. It had 2 Glandwashers? at .5 mm each and a large oil seal for unsealed bearing at 1.1 mm. I think this arrangement allowed the bearing to float 1.5 mm. I'm wondering if its had a narrower bearing fitted at some time, or the bearing seat has been cleaned out ( deepened ) or am i mising a piece. The gland washers have 4 quadrant marks on them. Since i'm getting a spacer made i was wondering if the marks have any thing to do with oil movement and should be replicated on the spacer.
Regards Longdon
Thanks Matty Someone has done a pretty fair job of repairing the gearbox splines and clutch centre splines on mine but the distance between the output bearing circlip and the bearingis about 3.6 mm. It had 2 Glandwashers? at .5 mm each and a large oil seal for unsealed bearing at 1.1 mm. I think this arrangement allowed the bearing to float 1.5 mm. I'm wondering if its had a narrower bearing fitted at some time, or the bearing seat has been cleaned out ( deepened ) or am i mising a piece. The gland washers have 4 quadrant marks on them. Since i'm getting a spacer made i was wondering if the marks have any thing to do with oil movement and should be replicated on the spacer.
Regards Longdon
Hi Longton
You probably have the "old" set of parts between the output bearing and big circlip. As far as I can remember these comprised, firstly the bearing which should have been press fitted at 150/200 DegC into the casing - in as far as the aluminium flange. Then there was an oil-seal, then a spacer which looked like a piston ring, then some thin slightly "crinkley" spacers/washers and finally the big circlip. Between the output gear and the chain sprocket is a spacer which acts as the inner for the oil seal.
There is now a much better arrangement which can be bought from Draganfly - at 01986 894798.
This comprises basically a new spacer with oilseal which fits between the bearing and the big circlip - with maybe the crinkley shims/spacers to take up any slack. This provides the correct spacing from bearing outer to the big circlip and should take up the 3.6mm slack.
I think the parts are 3112-96 and 3635-96 from Draganfly and cost about £16.
The oil-seal inner still runs on the spacer between the output gear and drive chain sprocket. A new one can also be obtained from Draganfly if your old one has a groove worn into it by the oil-seal, - though sometimes a good bit can be found by putting the spacer on the other way round !!.
The output bearing is a very unusual size by the way - 72mm outside, 1.5 inches inside and 17mm wide, and a sealed one (I left the seals in on mine) can be obtained at a reasonable cost from:-
Peter Barker - barkers@engrs.wanadoo.co.uk 01454 228066
If you look back to page 5, 20th December, (if I've got the page right) you will see that my old box, unknown to me, had been modified with a sleeve to take a standard sized bearing. This had worked for many years but eventually all worked loose and in the end I was lucky enough to find another gearbox casing and shrink in a new "special" but standard Burman sized bearing.
Hope this is of some help.
Matty
You probably have the "old" set of parts between the output bearing and big circlip. As far as I can remember these comprised, firstly the bearing which should have been press fitted at 150/200 DegC into the casing - in as far as the aluminium flange. Then there was an oil-seal, then a spacer which looked like a piston ring, then some thin slightly "crinkley" spacers/washers and finally the big circlip. Between the output gear and the chain sprocket is a spacer which acts as the inner for the oil seal.
There is now a much better arrangement which can be bought from Draganfly - at 01986 894798.
This comprises basically a new spacer with oilseal which fits between the bearing and the big circlip - with maybe the crinkley shims/spacers to take up any slack. This provides the correct spacing from bearing outer to the big circlip and should take up the 3.6mm slack.
I think the parts are 3112-96 and 3635-96 from Draganfly and cost about £16.
The oil-seal inner still runs on the spacer between the output gear and drive chain sprocket. A new one can also be obtained from Draganfly if your old one has a groove worn into it by the oil-seal, - though sometimes a good bit can be found by putting the spacer on the other way round !!.
The output bearing is a very unusual size by the way - 72mm outside, 1.5 inches inside and 17mm wide, and a sealed one (I left the seals in on mine) can be obtained at a reasonable cost from:-
Peter Barker - barkers@engrs.wanadoo.co.uk 01454 228066
If you look back to page 5, 20th December, (if I've got the page right) you will see that my old box, unknown to me, had been modified with a sleeve to take a standard sized bearing. This had worked for many years but eventually all worked loose and in the end I was lucky enough to find another gearbox casing and shrink in a new "special" but standard Burman sized bearing.
Hope this is of some help.
Matty
Longdon,
yes, you seem to be missing a pice. It looks like a piston ring. The rubbery seal fits loosely inside it.
The total width of the two washers and the piston ring-like spacer measured 3.95mm on my box
The order of assembly from the bearing outwards should be:
Bearing
Thin wassher with bumps facing out
Piston ring spacer with seal inside
Thin washer with bumbs facing in
Circlip.
This circlip is a struggle to fit. The little bumps on the thin washers have to push into the rubbery seal to stop it rotating. Untill these washers are pushed hard enough to squash the rubber and contact the piston ring-like spacer, the circlip won't go in the groove.
Tatty
yes, you seem to be missing a pice. It looks like a piston ring. The rubbery seal fits loosely inside it.
The total width of the two washers and the piston ring-like spacer measured 3.95mm on my box
The order of assembly from the bearing outwards should be:
Bearing
Thin wassher with bumps facing out
Piston ring spacer with seal inside
Thin washer with bumbs facing in
Circlip.
This circlip is a struggle to fit. The little bumps on the thin washers have to push into the rubbery seal to stop it rotating. Untill these washers are pushed hard enough to squash the rubber and contact the piston ring-like spacer, the circlip won't go in the groove.
Tatty
Hi Tatty and Brandon
Yes you are right Tatty about the original arrangement - I was not too sure exactly how it was meant to be - but the "crinkley" washers either side of the rubbery oil seal to stop it rotating is obviously the correct assembly. This oilseal was the same outside diameter as the output bearing and there should be a spacer looking like a piston-ring (for some reason I do not understand - why not just a spacer?) between the washers and the big circlip.
With the new spacer however, the new smaller outside diameter oilseal, is pressed into the new steel spacer which has a fairly tight outside fit into the bearing casing to stop it rotating. Then the assembly (possibly using the crinkley washers as shims) is held in tight with the big circlip.
I used a little smear of bearing Locktight on the outer of the spacer to ensure it did not move or leak.
The choice is yours - either system is no doubt OK.
Matty
Yes you are right Tatty about the original arrangement - I was not too sure exactly how it was meant to be - but the "crinkley" washers either side of the rubbery oil seal to stop it rotating is obviously the correct assembly. This oilseal was the same outside diameter as the output bearing and there should be a spacer looking like a piston-ring (for some reason I do not understand - why not just a spacer?) between the washers and the big circlip.
With the new spacer however, the new smaller outside diameter oilseal, is pressed into the new steel spacer which has a fairly tight outside fit into the bearing casing to stop it rotating. Then the assembly (possibly using the crinkley washers as shims) is held in tight with the big circlip.
I used a little smear of bearing Locktight on the outer of the spacer to ensure it did not move or leak.
The choice is yours - either system is no doubt OK.
Matty
Hi All
This is another important contribution which I heard about a few days ago, on why the 4th gear dogs on a Comet Burman box may not mesh properly.
I thought this reply might be useful to somebody, if I added it to this old thread - even after the thread was thought to be finished about a year ago !!
It seems that the bronze bush pressed into the output gear which the mainshaft runs in, sometimes works loose and moves inwards into the space where the sliding gear needs be in 4th. 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.
I did not know about this when I rebuilt my gearbox a year or so ago and did not check the bush location. I just have to hope that mine is OK - certainly my gearbox has worked fine for 4000 miles or so since I rebuilt it using the findings from this thread.
I have written an article which may be published in the VOC magazine next year sometime and this describes my gearbox rebuild and also summarises the steps I took to try to minimise the risk of 4th gear meltdown.
Happy Christmas and a Vinnie New Year
Matty
This is another important contribution which I heard about a few days ago, on why the 4th gear dogs on a Comet Burman box may not mesh properly.
I thought this reply might be useful to somebody, if I added it to this old thread - even after the thread was thought to be finished about a year ago !!
It seems that the bronze bush pressed into the output gear which the mainshaft runs in, sometimes works loose and moves inwards into the space where the sliding gear needs be in 4th. 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.
I did not know about this when I rebuilt my gearbox a year or so ago and did not check the bush location. I just have to hope that mine is OK - certainly my gearbox has worked fine for 4000 miles or so since I rebuilt it using the findings from this thread.
I have written an article which may be published in the VOC magazine next year sometime and this describes my gearbox rebuild and also summarises the steps I took to try to minimise the risk of 4th gear meltdown.
Happy Christmas and a Vinnie New Year
Matty