One of the issues carried over from the original bike was ''what exactly is the chain size'' and the state of the rear sprocket. The chain was a Renolds with no size markings and an old 420 seemed the right thing but it was hard to state 100% as the rear sprocket was so well worn, however a new 420 chain was just a fraction too tight on the teeth, it fitted but was a little 'clingy' so we used a 428 std chain in its place
This was ok although the clearance for the spring link was a little fine so rather than have the link to the outside it was mounted inboard temporarily.
Wanting a final solution I was prepared to put new chain and rear sprocket on, the only issue been where to get a sprocket certainly not off the shelf and then from the inter-web up popped 'Sprockets Unlimited'
All they asked was that I choose chain size .. 428 easy that bit, No. of teeth.. well original was 58 but as as some old wag at a trial suggested it was a tad highly geared I plumped for 60 this time. centre diameter.. now the original is a SUNG fit round the brake and even has a little machined off to make way for the bolts so out with the micrometer and a figure was agreed (after measuring 5 times to be certain) Then the bolt centres... again measured five times, they have to be spot on..
I've recommended other suppliers on this site before but these guys take the top award, in less than a week the thing arrived absolutely SPOT ON no margin of error whatsoever . It bolted straight on, very impressed. and the extra two teeth only add 8mm to the diameter so only the engine will know the difference.
As I bolted the wheel back in I took the time to add a 3mm spacer to the drive side spacer just to move the chain over and more easily clear the clutch case. If this is succesful I'll machine new spacers for the rear axle, I'm especially keen to make the one for the offside like a cup to offer some protection to the exposed bearing on that side of the hub.