G: Gearbox (Single - Burman) Burman Drive Sprocket Loose

Martyn Goodwin

Well Known and Active Forum User
Non-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 ?
 

Martyn Goodwin

Well Known and Active Forum User
Non-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.
 

Martyn Goodwin

Well Known and Active Forum User
Non-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

Well Known and Active Forum User
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

Well Known and Active Forum 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.
 

Marcus Bowden

VOC Hon. Overseas Representative
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.
 
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