Frame/engine numbers

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Mar 3, 2007
Hi all

This is my first post. I am just about to start restoring a 1971 Commando
but I do not have the original registration documents. The frame and engine number match with the engine number prefixed by 20MS3. Does anyone know if this is how it should be and what if anything the 20MS3 prefix means. Great site by the way, I can see myself being a frequent visitor in the future.

Cheers John
Hello John,

I think that you will find the prefix is actually 20M3S (or it should be!) *20M3* denoting a Commando model, and the the *S* means that the points and auto advance run off the camshaft, the housing being contained in the front part of timing cover. Early Commandos (20M3 prefix) had a different setup with the points and auto advance contained in a separate housing located at the inner rear of the timing chest behind the barrels and having its own chain drive. The factory eventually stopped using the 20M3S prefix, probably because it was rather pointless stamping every machine as they made no other models by then.
Hello John,

I asume from your mention of "Registration Documents" that you're UK based ?

Your first step should be to join the Norton Owners Club and get a dating certificate confirming what you've got. This will be in a form which is acceptable to the Licensing Authorities for obtaining an age-related number and "free" road tax ( You should get a "J" or "K" suffix plate I think).

A copy of a book such as Roy Bacon's "Norton Twins" and/or "Norton Twins restoration" would also be handy for explaining this sort of detail. They're not perfect and they don't tell everything but they're a good basis and a thoroughly good read if you want to know where your bike fits into the scheme of things and, perhaps more importantly, which parts are interchangeable between the model years. 1971 was quite an important cut-off in that respect.
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