Rear sprocket question

Wondering if anyone out there has figured a way to adapt a Norton rear drum to accept another sprocket, say something like the bolt on one used on Triumph conical hubs? Would'nt seem like too big a job to remove the old sprocket and fab up a flange, just welding it on without warping the drum beyond use??

MikeG said:

Wondering if anyone out there has figured a way to adapt a Norton rear drum to accept another sprocket, say something like the bolt on one used on Triumph conical hubs? Would'nt seem like too big a job to remove the old sprocket and fab up a flange, just welding it on without warping the drum beyond use??

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Yes, it's been discussed but there isn't a lot of meat on the drum area to make it feasible. With torquey bikes you can usually get all the adjustment with the countershaft sprocket.

Not so much gearing adjustments I'm after, just thinking of #1 an easy way to use 520 O ring chain, and #2 not having to replace a drum just because the sprocket teeth are worn.

MikeG said:

Not so much gearing adjustments I'm after, just thinking of #1 an easy way to use 520 O ring chain, and #2 not having to replace a drum just because the sprocket teeth are worn.

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You might do a search here for more details but the basics was that it's not worth the extra work. The cast iron lasts quite a while and is not hard to machine for the 520. And it's not all that expensive when you do need to replace.

Norvil sells a bigger OD ring of teeth for just this purpose and I had it adapted on to find out it will not work on a Cdo at the ~1/2 extra OD fauls shocks or swing arm. It may be possible to create all new teeth somehow but it just ain't cost effective. You can have my experimental drum to play with if ya like.

Thanks Hobot, but I have an old drum kicking around. Thats what got me thinking on the subject. There is a company called Rebel Gears that can make you pretty much anything you want for a sprocket. Wonder if there is enough meat on drum to machine in from the end and leave enough to get bolt hole into?? Or am I just reinventing a wheel thats already round? :?

The fasteners you can see sticking out around my attempt are about as small as possible, by spiting their threads in the mating seam. Weld would be better but tricky with the chain links coming so close to the ring bead area. . I have taken at least 3 out of the gene pool so far. I had the drum teeth milled down and maybe sprocket too to slip on then the seam drilled and tapped. Once i discovered it would not fit I did not bother to grind down the fasteners. On further inquiry to the older lists and Norvil they said it was a rare option on special off road bikes with special swing arms or shock mounts than factory. At some point we will run out of factory drum teeth so someone may have to take up the task if they ain't already, beside India iffy stuff.

It is easy to machine the old sprocket off and put a steel replacement in its place. The drum is cast steel so it will weld easily with a mig welder. Last one I did I just used 8 evenly spaced spot welds and alternated sides for welding. Cutting the drum and sprocket concentric is the hard part. A few thousandths run-out on the sprocket will make the chain whip severely.

And a good steel replacement sprocket will outlast a stock sprocket that has been narrowed by 2 to 1. Jim

i have just done this with an old cast rear drum for Bike # 2
Machined off the cast sprocket, machined up a fluted base ring that is sweated onto the cast drum, with spot welds done from the inside(where the brake linings would run) in through 'peep holes and machine this drum area so to make sure it is true.
Machine out some steel (or ali if preferred) sprockets and bolt to machined ring on drum
Smallest tooth count for the way I have done it is 44, (std cast one is 42)so will run a 22 or 23 tooth sprocket on the TTI gearbox to see where I am with gearing.
This maybe affected by the Maney belt primary drive, as there is a tendency to be a little higher in gearing there to start with, so all may equal out.
Gives me the options for changes at a wheel removal depending on track types.
Regards Mike