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Burman Sprocket

Vic Youel

Well Known and Active Website User
Non-VOC Member
I have just started to assemble my Gearbox for my Comet and immediately hit a problem. The old sprocket was very difficult to remove and is beyond use now. The shaft nut sits inside a recess in the drive sprocket. The nut is two inches across flats and is very difficult to get at. The original sprocket has a recess of 3 inches diameter whereas a new one I have recently acquired has a recess of 2 and 5/8 inches diameter. A very nice man from the west London section has lent me a clever spanner/tool with which to tighten it up properly. However it only fits the original 3 inch recess sprocket and not the new one with a smaller diameter recess.

(Note that my measurements only have the accuracy of a ruler and standard eyesight.)

Possible solutions to tighten up the nut include:

1. Prudent use of a hammer and chisel

2. Acquire a new box spanner that will fit my new sprocket

3. Modify the borrowed tool (with the owner's permission of course) which will severely weaken it

4. Machine out my new sprocket recess to 3 inches

5. Acquire a new sprocket with the 3 inch recess.

Assuming the sprocket I removed is made to the correct dimensional specification does anyone out there know whether it has been drawn under the drawings project and therefore can confirm the correct internal diameter of the recess? Further, does anyone know whether one made to the assumed correct 3 inch dimension been manufactured by the VOC spares company and is available from them?

I have not yet asked the spares company as they usually do not know details like this.

I have also asked the JTAN forum

Thanks

Vic
 
Last edited:

Comet Rider

Well Known and Active Website User
VOC Member
Burman Sprockets

Vic,
Try asking the guys at Dragnfly in Bungay, as they will probably know the answer for you.
Otherwise where are you? as I have a large ring spanner that fits...

Neil
 

Vic Youel

Well Known and Active Website User
Non-VOC Member
I live in Bracknell Neil, and will of course be searching for a good spanner at Kempton A/J tomorrow but your kind offer is very much appreciated. I had an amazing response from JTAN and have all sorts of options to follow.

As far as I can determine, at present, the available sprockets from the VOCSC and Vintech etc are not the same as the original ones and are made by the Holder organisation for Vincents and many other bikes. They fit though.

Best advice so far is to adapt a ring socket by grinding it to fit snugly and perhaps welding a good lever to it.

One enthusiast is working on reparing original sprockets with a much harder wearing set of teeth because the mass produced item by Holder seems to be rather soft and can wear rapidly (on twins as well).

Vvic


Cheers

Vic
 

Vic Youel

Well Known and Active Website User
Non-VOC Member
The VOC spares company and Vintech sprockets are supplied by Velocette (the Holder organisation) and are not the same as the originals. To get any reasonable spanner to fit they need machining.......that is the solution which I adopted.

Cheers

Vic
 
F

Flatout

Guest
Holder organisation.

The VOC spares company and Vintech sprockets are supplied by Velocette (the Holder organisation) and are not the same as the originals. To get any reasonable spanner to fit they need machining.......that is the solution which I adopted.

Cheers

Vic

Does anyone have a contact number for 'Holders' so then i can it to my list of suppliers?

Dave.
 

Robert Watson

Well Known and Active Website User
VOC Member
I tried (Well David Meadowcroft tried) for some time to find out the metalurgy Holder was using for his sprockets, to no avail. I did this because I found they just wore out far too quickly. At 10,000 miles they were done. (Yes I put 10,000 miles on the Woolly Mammoth last year) I now re-ring old sprockets with SAE 8620 case hardened sprockets, which at 10,000 miles show no wear. (Yes I put 10,000 miles on the Woolly Mammoth last year, and by the way the alloy rear sprocket is also still in great shape - Sprocket Specialists in the USA - 7075 and hard anodized although it only got about 8000 miles as a shattered brake drum meant using the other sprocket for a couple of thousnad miles) These rings are made by a small outfit that does nothing else but countershaft sprockets in the US for the dirtbike market. I really don't do it commercially and I have recently sent a batch of rings to the UK for a member there to do the same, although he is looking for a UK source of a similar solution. The rings are 2 1/2 ID so on the older Burman sprockets, unless going to a 520 chain, they will require a little grinding to clear a socket over the large nut. Having said that I am just about to do the sprocket from my A twin, and it has no recess but is full width from shaft to rim. As I am going to 520 chain I may save this for a 530 rebuild and find a recessed one instead. I mostly started this to do postwar twin sprockets as they are more complicated to make with that seal boss to consider. I have found one where the seal boss ran more than .020 out of concentricity with the bore. I bet the guy who had that on his bike could never figure out why it leaked!

Robert
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Sprocket wear

Although it is far from intuitive, if a hard material is run against a soft material IN THE PRESENCE OF ABRASIVE, then the hard material wears fastest. The soft material picks up and holds the abrasive particles, and grinds the hard material away. Beyond the memory of most of us but "a set of wooden brake blocks'll last the life of a farm-cart, but the smith is always busy putting new iron tyres on carts".
 

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