Should I buy?

Hi Paul and welcome.

My project is a Dec 1971 750 Roadster 200*** later than yours, just. I asked the same question. No expert, but I believe from my research that the combat engine first appeared in 1972 under a 20**** number, so you almost certainly have a pre-combat model. I'm sure others more knowledgeable will give you the precise date and number. I think the 20M3S number refers to the adoption of points on the timing cover at the end of the cam shaft.

Hi Paul,

Roy Bacon's book "Norton Twin Restoration" puts the first Combat engine as 200976. I would not be concerned even if it was a Combat as most of these were subsequently detuned, and in 40 years without an accurate record kept by previous owners, who knows what is inside. Early Commandos had silver barrels and the Combat was denoted by black barrels.

20 = Atlas 20M3=Commando (distributor) 20M3S Commando (camshaft points)

If you dig into this web page a little deeper, under "models" you will find Commando and clicking on that will reveal a decent amount of details to establish exactly what you are looking at.

Just one slight point is that my 71 pre Combat came with black barrels. Judging by the rust on them, I guess from new, although they could have been painted by someone wanting a go faster engine.

If this is a Combat engine, I wouldn't worry. The original main bearings will have clapped out long ago, and likely have been replaced with the Superblends which fix the problem. If it IS a Combat, you'll have to buy more expensive premium petrol, but once the main bearings have been fixed, there shouldn't be a problem.

Of course, some "De tuning" of Combats was misguided. The Combat had higher compression, so replacing the stock Combat '2S' cam with one from a non-combat engine would be counter-productive, leading to more pinking under acceleration.

Previously wrote:

Hi All,

New member seeking help! Have the chance to acquire a Norton Commando 750

Dated Nov. 1971. Engine No. 20M3S 15***8

Would this be a "Combat Engine"?

20M3S engine would have from new 30mm carbs, combat would be 32mm.