Burman 4th Gear Selector Meltdown
- Thread starter tatty500
- Start date
Hi all
Much water has passed under bridges since the original investigation into the "4th gear burnout problem" some time ago.
At the time I checked the damaged gearbox parts sent to me by I think Tatty 500 and though the 4th Gear dogs were a bit tapered when I assembled the gears into my casing but they seemed to engage by about 2.5 at least, which was about the same as my gears which had not been any problem.
However I optimise the end floats etc. on my box to ensure that I did not get a 4th gear problem and my box ( with a second hand replacement casing because mine was cracked and leaked) worked fine for 10,000 miles or so.
Then a couple of weeks ago my box started to whine and grind horribly in 1st, 2nd, and 3rd gears and I found that the driveside layshaft bush had seized and severely damaged the casing.
This has been repaired by a very competent local engineer (bored in line and a new oversized bush fitted ) and now has been rebuilt and is quiet and working fine.
BUT when rebuilding the box I thought a bit more LATERALLY and think I now understand why the apparently good damaged parts from Tatty500 had failed.
It was probably the VERY WELL KNOWN Burman problem of the gear indicator pressing on the gear lever in 4th and not allowing the gear to fully engage. This is caused by the gear lever being one spline too far round (upwards) so the dogs are not fully engaged and put great pressure on the selectors, causing them to overheat with friction and sieze onto the sliding gear.
Does this look likely as the cause of the 4th gear problems experienced by a few people?
Matty - perhaps a few years late with the real answer !!!
Much water has passed under bridges since the original investigation into the "4th gear burnout problem" some time ago.
At the time I checked the damaged gearbox parts sent to me by I think Tatty 500 and though the 4th Gear dogs were a bit tapered when I assembled the gears into my casing but they seemed to engage by about 2.5 at least, which was about the same as my gears which had not been any problem.
However I optimise the end floats etc. on my box to ensure that I did not get a 4th gear problem and my box ( with a second hand replacement casing because mine was cracked and leaked) worked fine for 10,000 miles or so.
Then a couple of weeks ago my box started to whine and grind horribly in 1st, 2nd, and 3rd gears and I found that the driveside layshaft bush had seized and severely damaged the casing.
This has been repaired by a very competent local engineer (bored in line and a new oversized bush fitted ) and now has been rebuilt and is quiet and working fine.
BUT when rebuilding the box I thought a bit more LATERALLY and think I now understand why the apparently good damaged parts from Tatty500 had failed.
It was probably the VERY WELL KNOWN Burman problem of the gear indicator pressing on the gear lever in 4th and not allowing the gear to fully engage. This is caused by the gear lever being one spline too far round (upwards) so the dogs are not fully engaged and put great pressure on the selectors, causing them to overheat with friction and sieze onto the sliding gear.
Does this look likely as the cause of the 4th gear problems experienced by a few people?
Matty - perhaps a few years late with the real answer !!!
Matty,
I don't know whether the pointer was ever a problem on my box as both bits were missing. I seem to remember (from different bikes 40 years ago) the pointer parts being made of fairly soft alloy.
When making the change into top, the lever is down when the pointer moves to 4th position and would get clouted when the pedal returns to mid position. It would be a battle of springs and pointer to decide whether the selector shaft would move out of gear a bit.
So yes, it's not impossible that the wear pattern on my dogs was cased by under-engagement years ago....but it must have been in such a state for many a mile.....and there were several owners that must have all failed to notice the pointer before it went missing.
Tatty
I don't know whether the pointer was ever a problem on my box as both bits were missing. I seem to remember (from different bikes 40 years ago) the pointer parts being made of fairly soft alloy.
When making the change into top, the lever is down when the pointer moves to 4th position and would get clouted when the pedal returns to mid position. It would be a battle of springs and pointer to decide whether the selector shaft would move out of gear a bit.
So yes, it's not impossible that the wear pattern on my dogs was cased by under-engagement years ago....but it must have been in such a state for many a mile.....and there were several owners that must have all failed to notice the pointer before it went missing.
Tatty
A few questions. 1) What was the cause and cure for the noisy third gear?
2) One poster mentioned thixatropic grease. Can you suggest specific brands, especially one available in USA, please?
3) Also, a friend who does a lot of Ariel work (Burman Gearboxes) raves about the Grease that he gets from Draganfly (p/n OI-GRB "Semi-fluid grease 800 gms, sufficient for 1 gearbox"). He says it really makes them work well and does not leak. I do not know what brand it is, but he is very partial to it.
Thank you for the interesting article.
2) One poster mentioned thixatropic grease. Can you suggest specific brands, especially one available in USA, please?
3) Also, a friend who does a lot of Ariel work (Burman Gearboxes) raves about the Grease that he gets from Draganfly (p/n OI-GRB "Semi-fluid grease 800 gms, sufficient for 1 gearbox"). He says it really makes them work well and does not leak. I do not know what brand it is, but he is very partial to it.
Thank you for the interesting article.
Hi All This is Matty who has noticed that someone has a Burman problem.
As you can see a lot of thought has been given to the gearbox over the years but I there is more information on the Forum when I can find the time to look for it.
I have used grease from Draganfly with success - despite their warning that it may contain nuts !!
I have recently used grease from Classic lubricants called PENRITE which is OK.
However it still leaked from the drive side, so I bought the bearing spacer with an oilseal from Draganfly BUT had a thin groove cut onto the outside and fitted a large diameter O ring to act as a seal. Think this is mentioned on the forum somewhere.
I replaced 3rd gear but still noisy until I replaced worn bronze layshaft bushes which allowed the shaft to run out of line and gears to mismesh.
Have to rush off to play in a Jazzband now and may have more to say when I have more time.
Matty
As you can see a lot of thought has been given to the gearbox over the years but I there is more information on the Forum when I can find the time to look for it.
I have used grease from Draganfly with success - despite their warning that it may contain nuts !!
I have recently used grease from Classic lubricants called PENRITE which is OK.
However it still leaked from the drive side, so I bought the bearing spacer with an oilseal from Draganfly BUT had a thin groove cut onto the outside and fitted a large diameter O ring to act as a seal. Think this is mentioned on the forum somewhere.
I replaced 3rd gear but still noisy until I replaced worn bronze layshaft bushes which allowed the shaft to run out of line and gears to mismesh.
Have to rush off to play in a Jazzband now and may have more to say when I have more time.
Matty
I use Morris 140 straight cut gear oil in my Comet as it is an oil filled Burman ( it has a drain plug in the bottom). I have used Morris semi fluid grease in the Comet I am building for a friend. John
Hi
Not sure if 140 Gear oil is really OK with bronze layshaft bushes in Burman.
I have been told Hypoid 140 back axel oil contains chemicals which damage bronze.
I gather using the incorrect type of 140 was the main cause of damage to the rear drive of the S8/S7 Sunbeam shaft drives.
No doubt some lubricants expert can cast more light on this.
Matty
Not sure if 140 Gear oil is really OK with bronze layshaft bushes in Burman.
I have been told Hypoid 140 back axel oil contains chemicals which damage bronze.
I gather using the incorrect type of 140 was the main cause of damage to the rear drive of the S8/S7 Sunbeam shaft drives.
No doubt some lubricants expert can cast more light on this.
Matty
Hi
Have had a look a this long missive about problems with The Comet Burman Gearbox.
I think most things have been covered one way or another if you have time to wade through it all.
Between us we have put in to this most of the things I and others have found about the tolerances of the shafts, curing grease leaks with different bearings and spacers with an oil seal at the sprocket drive end eg.
The spacer/oilseal from Draganfly leaked a bit round the outside so as stated, I had a very small groove about 25 thou wide turned into the outside of the spacer which is held in against the bearing with a big circlip and put in a large diameter but very thin (25 thou) O ring into the groove. This seems to have fixed the grease leak because it was then a tight fit into the bearing housing.
The slop in the splines in the centre of the clutch has been mentioned - just do the nut up very tight with some Loktite,
A contributor from Austria had a fix for the grease leak from the gear change shafts. This is not 100% fixed but vastly better after modifying the gear shaft bearing and adding some ORings. (details are in another thread I think).
Anyway my Burman box after around 3,000 miles now seems to be very good but not after quite a bit of heartache to get it right.
Hope all this is of some help to someone - though I did publish an article in MPH some while ago which covers most of this and probably have a copy on my computer somewhere if anybody is interested.
Matty
Have had a look a this long missive about problems with The Comet Burman Gearbox.
I think most things have been covered one way or another if you have time to wade through it all.
Between us we have put in to this most of the things I and others have found about the tolerances of the shafts, curing grease leaks with different bearings and spacers with an oil seal at the sprocket drive end eg.
The spacer/oilseal from Draganfly leaked a bit round the outside so as stated, I had a very small groove about 25 thou wide turned into the outside of the spacer which is held in against the bearing with a big circlip and put in a large diameter but very thin (25 thou) O ring into the groove. This seems to have fixed the grease leak because it was then a tight fit into the bearing housing.
The slop in the splines in the centre of the clutch has been mentioned - just do the nut up very tight with some Loktite,
A contributor from Austria had a fix for the grease leak from the gear change shafts. This is not 100% fixed but vastly better after modifying the gear shaft bearing and adding some ORings. (details are in another thread I think).
Anyway my Burman box after around 3,000 miles now seems to be very good but not after quite a bit of heartache to get it right.
Hope all this is of some help to someone - though I did publish an article in MPH some while ago which covers most of this and probably have a copy on my computer somewhere if anybody is interested.
Matty
file:///C:/Users/John/Documents/New%20folder%20(2)/File-1458213281.pdf
This oil is supposed to be ok with phosphor bronze, it's not hypoid oil..John