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G: Gearbox Burman Drive Sprocket Loose


John Smith-Daye

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VOC Member
So its off to Bungay you go then John - or Beccles, if your name is Len and you get it a bit wrong................
 

nkt267

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So its off to Bungay you go then John - or Beccles, if your name is Len and you get it a bit wrong................
Luckily John i found a good output gear and mainshaft sliding gear in my Burman spares box, a new sprocket is on it's way too..
 

oexing

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VOC Member
I knew that this is a critical place requiring a good fit for avoiding wear and any troubles that go with it. So a few months ago I did a LOT of laser welding at my former company on most of the splines in the Rap gearboxes - doing two of them parallel. The welding for the sprocket fit should take just max. half an hour for a lowly toolmaker. But then you have to set up a mill plus dividing head for producing a precise push fit there, takes some time to do this right. But nevertheless I believe this to be essential in the long run. So when you get all parts for your box do check that all is well, don´t take compromises, do it right. The hard weld from laser welding can be milled with a modern coated carb end mill for 60 HRC, face milling, I did it by grinding on a HF spindle on the mill, nice and slow.
I could have had new spares from the Spares Co. but honestly I don´t have much confidence in getting that sort of fit I´d like to see - for that money.

Vic

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MartynG

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VOC Member
I knew that this is a critical place requiring a good fit for avoiding wear and any troubles that go with it. So a few months ago I did a LOT of laser welding at my former company on most of the splines in the Rap gearboxes - doing two of them parallel. BIG SNIP..
I could have had new spares from the Spares Co. but honestly I don´t have much confidence in getting that sort of fit I´d like to see - for that money.
Sounds like a proper solution IF and its a big IF you have the required equipment and skills. I figure to pay a specialist shop to do that work would cost more than the new part from Draganfly - the chap I use and trust charges $100 per hour for his time PLUS $50 per hour for machine time. OUCH!

When it works loose again I am planning on trying Loctite 660 - anyone had experience with this grade?? Or is it something else I should try?

Info on it is here http://www.loctite.com.au/3320_AUE_HTML.htm?nodeid=8802627715073

ta

Martyn
 

Matty

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VOC Member
Hi
I have had my Comet for 62 years now and rebuilt the Burman gearbox 3 or 4 times for various reasons but never had a problem with the drive sprocket splines.
However I have always found that the nut which holds the clutch basket to the mainshaft had always worked a bit loose and damaged the splines in the clutch basket, no matter how tight I had hammered up the big nut.
Some years ago I had to replace the clutch basket for this reason but fortunately the obviously harder (and very expensive) gearbox mainshaft was OK.
I feel that the design is rather poor in this area and any shocks on the clutch are bound to try to undo the sprocket nut a little and allow a little slop to develop over time and think that the same will also apply to the output drive sprocket.
Matty
 

Matty

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PS
So far I have never used LOCTITE on either of the gearbox splined shafts, but it may be some time (hopefully) before I find out if my last gearbox rebuild about 6 years and "25,000 miles ago has allowed slop to happen with the splines!!
Maybe LOCTITE next time ?
Matty
 

vibrac

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VOC Member
I am no A expert but it was pointed out to me recently that A box clutches had rubber bushes to reduce the harshness of the drive which brings be me back to the Norton vane clutch perhaps this sprocket hammering was an additional fault of not having the cushion
 

nkt267

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VOC Member
I am no A expert but it was pointed out to me recently that A box clutches had rubber bushes to reduce the harshness of the drive which brings be me back to the Norton vane clutch perhaps this sprocket hammering was an additional fault of not having the cushion
A lot of early Burman chainwheels had rubber bushes in them to soften the take up when the clutch is released..My brother-in-laws 250 OK Supreme had them,or should I say did not have them just bolts with 3/4" slop..all the parts were bought from Draganfly motorcycles. It made the hand changes a lot nicer..John
 

A_HRD

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VOC Member
I am no A expert but it was pointed out to me recently that A box clutches had rubber bushes to reduce the harshness of the drive which brings be me back to the Norton vane clutch perhaps this sprocket hammering was an additional fault of not having the cushion
Yes Series A machines certainly did have the rubber clutch bushes. Six as standard but the number could be varied up to 8. But remember there was no ESA, so these bushes were essential. Available from me if you want them.

Peter B
 

Piston Pete

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With the first to go I suspect that it was of inferior quality - the latter ones were of high quality and cost! I suspect that on a single there is more 'shock' on the primary chain than on a twin - plus we all know how well the ESA does (not) work - and that translates to impact loading on the drive gear splines.

So now at every chance I get I am checking that retaining nut - though there is no way I would go more than 5,000 miles without checking it.

M
Hi Martyn - I have gone through 2 Burman gearbox sprockets , just as you describe ( I have done 40,000 miles on the Comet) - both times have left me at opposite ends of the country (Ireland) .Fortunately it hasn't happened on any of our longer trips abroad! . Anyway, I am preparing the Comet for this years international , and I was wondering if there is any way to check the sprocket for "rocking" on the splines without having to strip out the primary side ? The most recent sprocket was a very tight fit , and has about 2,000 miles on it. I cant see any way to avoid taking the primary side off, but its worth asking.
 

MartynG

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VOC Member
Hi Martyn - I have gone through 2 Burman gearbox sprockets , just as you describe ( I have done 40,000 miles on the Comet) - both times have left me at opposite ends of the country (Ireland) .Fortunately it hasn't happened on any of our longer trips abroad! . Anyway, I am preparing the Comet for this years international , and I was wondering if there is any way to check the sprocket for "rocking" on the splines without having to strip out the primary side ? The most recent sprocket was a very tight fit , and has about 2,000 miles on it. I cant see any way to avoid taking the primary side off, but its worth asking.
Hi Pete, Problem as you have found is that the drive sprocket PR50-22A is behind the inner primary case T4/2. If you are very agile and flexible (and that is NOT me) you may be able to reach in to that area with a long flat blade screw driver to see if there is any discernible side to side wobble. Come to think of it, if you drained the fuel and oil , using suitable cushioning you could lay the bike on its side to make it a bit easier to gain access - I have NOT tried to do this - just a thought.

I now carry as part of my standard touring spares a new drive sprocket and a new driving gear lock washer. In the interest of preventative maintenance I fit a brand new lock washer every time I replace the sprocket - cheap insurance.
 

Matty

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VOC Member
Hi
This still seems to be a problem for some, but I have never had a problem with the sprocket splines on my Comet in the 61 years I have owned it.
I replaced the worn sprocket about 30 years ago and have done a lot of work on the gearbox since for other reasons but still have this second sprocket on the box after about 50,000 miles and the splines still looked good the last time I had the gearbox apart around 2 years ago.
I wrote my findings on this post about a year ago and hope that all is still well because it is a lot of work to take the primary driveside of the bike apart just to find out if any slack has developed.
Will ride up to Liverpool from Essex for the Classic TT/VMCC Manx rally in August for about the 40th time and hope it all holds together as usual !!!
Happy New Year
Matty
 

oexing

Well Known and Active Website User
VOC Member
Someone asked about use of Loctite on the sprocket fit, but no experience on this so far? I am a big supporter of Loctite but cannot tell if this application may be great. But then, in case of a loose fit I´d try this anyway - after a good degrease and 638 on all faces . Either this works - great - or it does not . You will find out after some mileage and this "bodge" would not do any harm while trying. If Loctite shows to be suitable you will some day want to have a look into the gearbox eventually. Now you will have to deal with high strength Loctite. So before using the Loctite method the question is: Can you get a good puller onto the sprocket for extracting it ?? I cannot tell, not my type of bike. Just thinking . . .
But then, a torch for heating the sprocket to 300 degrees C would do and the sprocket would be scrap anyway due to poor fit.

Vic
 
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ray vinmad

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VOC Member
A spline is basically a multiple key set up to overcome higher loads. For that to work & transfer the greater loads, all the castellations must accurately match the slots & due to that necessary accuracy is only likely to occur on a `new' set up without any wear. With high reciprocating loads, if only two spline flanks are making proper contact it will eventually fail enough for another flank to start making contact in one direction & a different flank helping with the loads in the opposite direction and so on until they are all sloppy. Unless the general flank fits are all good to start with, a tight nut will not do much once fretting starts. Tightening/over tightening the nut will only help maintain a `good' fit. The nut is there to create end friction on the items unless it squeezes so hard it distorts the splines!
Probably Loctite is the only answer for serious mileages.
Having said that many modern bikes have the sprocket retained by a circlip and is a sloppy fit to start with.

Ray
 

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