James Fanning wrote:-My Mk1A Commando came out of the factory in Sept '73 and engine number is actually 140 numbers before the Mk1A was supposedly launched according to Norton records but specialist books mention that engines were often taken out of sequence on the factory assembly line so many anomalies exist. Mk1A was the first "noise control" model with bean can silencers and special airbox. Mk2A is virtually the same except with slightly smaller Interstate tank and had some mod to eliminate a problem with third gear - my third has an audible whine although has been like that for years and doesn't seem to get any worse.
My 850 has an anomaly too: a large 27 litre petrol tank with bean can silencers and big plastic airbox. Maybe it's a Mk1A too, though? What's the range on numbers of the Mk1A?
You've got a Mk1A , Juha.…
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You've got a Mk1A , Juha. 850 Commando engine numbers according to Norton records go as follows:Mk1 300,000 April '73Mk1A 306,591 Sept '73Mk2 + Mk2A 307,311 Jan '74Mk3 325,000 Feb '75Yours is an early Mk1A , only the 9th bike according to the numbers - but mine is even earlier at minus 140 ! The large Intersate tank (about 5.5 imperial gallons = 25 litres) was changed for the slightly smaller one (about 5 gallons = 22 litres) subsequent to the Mk1A but not sure if all Mk2A's had them or only later ones - certainly by the time the Mk3 came out they were all the smaller Interstate tanks. Your 27 litres measured corresponds to what I've read about variations often found in the large tank capacities.There were less than a thousand Mk1A's produced while the Mk2A's were several thousand. The Mk2 , as far as I believe , was a special batch of export models to America with US specs , around 700 or 800 bikes I remember reading somewhere. Mk1A's also had silver barrels while the 2A barrels were black.Run my Mk1A with peashooter silencers. Recently replaced the original carbs with a pair of the new Amal Premier Mk1 concentrics which transformed the bike , eliminating years of unreliable slow running - starts better , choke can be opened much sooner , ticks over evenly at 900 rpm and never stalls at the lights !