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G: Gearbox Burman Drive Sprocket Loose


MartynG

Well Known and Active Website User
VOC Member
In around 80,000 miles of use I have gone through 3 drive sprockets (PR50-22A) on the Burman gearbox fitted to my Comet. What fails is the splines on the inside of the sprocket that engage with the gearbox drive shaft. Fortunately its the 'steps' on the inside of the sprocket that wear away and not the splines on the drive shaft itself. First time I experienced this I was stuck on the side of the road having lost all drive. On disassembly the inside of the drive sprocket looked like it had been machined - perfectly smooth with not a trace left of the engagement splines!

Its less than 1,000 miles since I last replaced the sprocket, including fitting a brand new PR50-17 -1BA lock washer but again I find there is discernible 'play' with movement of the sprocker relative to the drive shaft.

Is there some 'secret burman business' to getting this area secure so that it the retaining nut PR50-218X does not work its way loose ?
 

MartynG

Well Known and Active Website User
VOC Member
This is the nut I'm talking about (it takes a 52mm impact socket) - and despite getting it as tight as I dare, and using a lock tab washer, it always seems to develop a bit of free play.
1516771230558.png
 

greg brillus

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VOC Member
Martyn it sounds like a poor quality sprocket............When you installed the new ones was the fit on the spline a nice snug fit..............?............I've not found twin ones to do the same. They do get some play in them but not like that. Cheers.............Greg.
 

MartynG

Well Known and Active Website User
VOC Member
Martyn it sounds like a poor quality sprocket............When you installed the new ones was the fit on the spline a nice snug fit..............?............I've not found twin ones to do the same. They do get some play in them but not like that. Cheers.............Greg.
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
 

vibrac

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VOC Member
I seem to remember reading that a version of this fault was the reason the Norton clutch got its rubber bung centre
 

erik

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VOC Member
if you bond the sprocket with locktite on the shaft?dismantling is easy if you heat up the sprocket.regards Erik
 

greg brillus

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VOC Member
If the new sprocket has any backlash at all on the shaft spline it will loosen the nut and the sprocket will hammer back and fourth.........There must be something like this happening for this to keep repeating itself. It is certainly showing no signs of this on the input shaft spline.
 

Marcus Bowden

Well Known and Active Website User
VOC Member
I drill & tap each hexagon corner 3/16" or 2 BA use a grub screw or just Alan head screw with first few threads turned down to core diameter to penetrate into sprocket or pinion behind, half time pinion was the last I did as it came loose. All with loctite of course.
Bananaman.
 
Last edited by a moderator:

MartynG

Well Known and Active Website User
VOC Member
If the new sprocket has any backlash at all on the shaft spline it will loosen the nut and the sprocket will hammer back and fourth.........There must be something like this happening for this to keep repeating itself. It is certainly showing no signs of this on the input shaft spline.
Sage Advise - If it happens again I will replace the 33 Tooth Drive Gear PR50-15BA as well
 

nkt267

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VOC Member
Just picked myself up off the floor after seeing the price of a replacement Drive Gear!
And not in stock. I stripped a BAP yesterday on a Comet I'm doing for a friend and half of 6 teeth on 15BA are missing,sifting through the grease to see if there are any bits in there now. luckily i found a good one in my boxes of miscellaneous gearbox bits..John
 

nkt267

Well Known and Active Website User
VOC Member
Well, if anyone wonders if semi fluid grease gets to every part of a Burman gearbox, having just spent 2 hours cleaning it out, IT DO.
No lumps of metal found from the damaged gear, but if you like metal coffee i can supply lots of 'grounds'.
I had a thought about worn splines and loose sprockets. If a replacement output gear is not available would an epoxy repair like JB weld or Loctite 660 do till a part became available.
I know that this is ok for keyways. I would certainly try it on my bike if i had to. The tricky part would be in making sure that the epoxy would not get into the gap between the output gear and the bearing spacer. Lightly oiling the sprocket 'should' stop the sprocket sticking to the epoxy..
 

Chris Launders

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VOC Member
I hate to say this but I have done it, if your sleeve gear splines are shot get a new sprocket and tighten it up and weld it to the nut and the nut to the shaft. When you eventually get a good shaft you can cut the welds off and get the old one out. Obviously, the weld needs to be done and cooled as fast as possible.
 
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nkt267

Well Known and Active Website User
VOC Member
The Draganfly part # is 3080-34 ; and they do have stock. Attached is the Draganfly cross-list for Burman part numbers
Thanks Martyn..When you type the part No you gave into the search box it comes up. When I looked at the parts diagram for BA boxes the output gears were shown but not listed in blue, where stock levels and price are found, which is why I assumed they were not in stock..
 

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