Norton 650SS late model gearbox sprocket

I will look at the Atlas Tomorrow   .

The gearbox sprocket width changed from 1/4" to 3/8" after 1964. Many owners upgraded their drive set-up to the wider sprockets as these seemed to last longer. The 3/8" x 5/8" gearbox sprocket will fit both the Dominators and 750 Commandos. The only significant change being the screw thread for the nut locking plate changing from 2BA to a  28tpi UNF item..The Dominator Service Notes say this thread originally was 3/16" BSF. The difference between BSF, BSC and BA for this size is quite small.

The most likely cause of chain rub is a poor quality chain beginning to exhibit side play. This unfortunately includes current versions of Renolds chain.

Unless you are planning on riding great distances and getting very throttle happy a 1/4" wide chain and sprockets would be fine for your bike.

.. was just contacting the primary inner case on my ES2. I found it was the split link - the extra thickness of the clip and plate just made that difference. I solved it by fitting the split link from the back instead - a bit tricky getting the clip on through the spokes but doable.

Russell & Ian........don't take a chance if you are planning long journeys. In the last 20 years of serious riding, all of my ride failures were down to Renolds chains throwing the split link spring (due to rubbing/catching). On each of these the chain had so much side-play it was whacking the chainguard walls. At an MoT a few years ago even the  Tester noticed the side-play on a chain that only had around 500 miles of use. In recent years the quality has got far worse and despite regular maintenance, after about 3,000 miles each chain was clapped out. The last straw was purchasing another news (Renolds) rear chain and on stretching it out on my workbench found that not only did some links wobble but the end of the chain could be pulled over about 6". I went out and bought a German 530 replacement which has now covered 1,500 miles with little obvious wear.

See the attachment showing a Renolds Primary after next to no miles of use. 

Renolds do not support motorcycles as an application for their chains, they do allow one distributor to buy chain from them and box it in Renolds boxes but oddly when you approach Reynolds directly they will not recommend any of their chains for motorcycle use. Take of that what you like but my take is avoid like the plague and use chain from someone who does make chain specifically for motorcycle use, so The Chainman's recommended chains or DID as one of the other better makers.

When you look at the old brands like Lucas, Girling, Jones etc that are being licenced for use on boxes for selling new dubiously sourced products you need your wits about you to work out the trustworthy products and sources.

Just a random thought, would fitting a bigger box sprocket  move the chain  line further out and avoid it circumcising the alloy box casing?. Had a look at the Atlas (67)  and its definately 3/8".

Hi Russell. If on your way to/from Austria you need any help , I am in Kent ,feel free. I will PM a phone no.  BOB.

.. Renolds any more as I've heard too many bad reports. The Chain Man is a good source of advice and chains. And by the way it's not good practice to mix manufacturers as dimensions like pin diameters and lengths may vary fractionally.......

Very few modern motorcycle chains supplied for classics are to the original motorcycle spec. Look it up and you will see why, as they would need to down spec the current chain. 

Even Andy the chain man's chains are non motorcycle spec - feel free to ask his supplier at IWIS. IWIS & JWIS and Renold exceed the strength spec of the motorcycle spec, but do not conform to construction dimension, and thus the difference due to thicker side plates used in construction. Regina, DID, TSUBAKI also make motorcycle chain, but again it differs to the original spec. The reason being that in other motorcycle applications there is sufficient clearance so the extra dimension of side plates is not an issue like it is on Nortons.

To get chain manufactured to the motorcycle chain spec would be very expensive and result in a chain that is weaker (though the same as what was used originally in the 70's) than the markets current non motorcycle spec offerings. And yes, I have asked. It would also fit commercial applications where the higher spec chain is needed, so I would expect there is no appetite for chain manufacturers to produce it even if asked due to safety issues.

Considering some modern bikes use 1/4 chain in some serious on and off road bikes suggests it has adequate strength. 

Went to Norway last year.  Super expensive ,and very wet.  Interesting people though.