MkI, MkII or MkIIA?

Just bought (but not actually collected, so can't look at more than the photos) an 850 Commando. The frame plate gives date of manufacture as 12/73. The frame and engine numbers are 312329. It was originally sold in Canada. It has the perforated metal air filter cover and reverse cone silencers, roadster tank & side panels and the taillight with the large rectangular lens (same as T140s, T160s etc).

Is it a MkII? Furthermore, what practical differences are there between the 80 MkIs/IAs and the MkIIs/IIAs? I've gained the impression that the MkIIAs were de-tuned in comparison to the MkIIs (or was it the MkIs?)

Congrats! I have a 7/73 850 that is one of the most enjoyable bikes to ride. Don't worry about detuned (2hp?) plenty of torque smooth power

Tigernut said:

Is it a MkII? Furthermore, what practical differences are there between the 80 MkIs/IAs and the MkIIs/IIAs? I've gained the impression that the MkIIAs were de-tuned in comparison to the MkIIs (or was it the MkIs?)

Click to expand...

The Mk1A and Mk2A are easy to spot, having a lefthand side cover and battery tray that was only on those models along with the plastic airbox.
My Mk2A is 311032 with a 12/73 tag.
Both the Mk2 and Mk2A were built at the same time from late 1973 to late 1974 so only a dispatch record (if available, some were lost) will indicate the model if it was unknown for some reason.

The metal air cleaner would be a clear indicator on a non A model.

312329 would be a Mk2 / Mk2A number as that general model started at 307###.

The above info is correct.

Your bike certainly sounds like it was built as a Mk2 850 Roadster. Many might say this is the best all round Commando. I have owned one for 46 years.

( Although I very much like the look of early Fastback models, the S models and an Interstate tank is very very useful if you do any touring)

Definitely do not beleive 90 % of what is said on the Norton Commando Facebook pages on how to tell an A model vs standard. For some reason almost every bike is called an A version when photos show it is not.

I have a full page copy of the Norton dispatch records for my Mk2 from August 1974. It shows Mk2As, Interpols and Mk2s all being built on the same day. A batch of 2As and Interpols built first and then a batch of Mk2s. Sequential engine and plate numbers but different assembly batch noes.

As Time Warp said the differences include

The hamcan airbox on the Mk2 versus plastic airbox on the Mk2 A

The East West mounted battery on the Mk2A to make space for the plastic airbox

The left hand side cover with the plastic duez fastener at the bottom left on the 2A. Later correction. - Bottom right side corner of the sidecover!!! These sidecovers seem to have a habit of falling off and replacements are hard to find.

The annular discharge exhaust mufflers.

To compensate for the airbox and mufflers the Mk2A had 220 (or 230 ???) Mainjets vs the Mk2 260s. I can't remember if the slides and needle positions are different. These days almost all A model mufflers have been replaced with peashooters so the original A setting may no longer be correct.

Details which DO NOT differ between the standard and A models despite what is often recorded on Facebook are the gearbox second gear pair. These were changed on both models at the same time. Norman White says this happened in late 1973 from 306591 on.

Also the rear chainguard was changed slightly on both models about the beginning of 1974 to include a small notch which allowed access to the small inspection cap on the rear brake plate. I understand this was for new regulations in the USA. It is not as some Facebook posts will say different on A vs standard bikes.

The A models were built to meet stricter noise and environmental rules. Firstly for Continental Europe. But in the end they went all over the world including the USA.

Tigernut said:

Just bought (but not actually collected, so can't look at more than the photos) an 850 Commando. The frame plate gives date of manufacture as 12/73. The frame and engine numbers are 312329. It was originally sold in Canada. It has the perforated metal air filter cover and reverse cone silencers, roadster tank & side panels and the taillight with the large rectangular lens (same as T140s, T160s etc).

Is it a MkII? Furthermore, what practical differences are there between the 80 MkIs/IAs and the MkIIs/IIAs? I've gained the impression that the MkIIAs were de-tuned in comparison to the MkIIs (or was it the MkIs?)

Click to expand...

"1974" MK2. Norton had no model years in the normal sense. Since you have the "hamcan" air filter, assuming it is original, it's not an "A" - they had a plastic air box. Your "frame number" is actually the certification label (VIN Plate/Frame Plate) number. The frame number is stamped into the timing side metal of the headstock and will be something like 850 F xxxxxx where xxxxxx does not match the engine serial.

Learn more:

Thanks for all the info so far. Next thing to ask is about the heads - I see RH4 and RH10 listed but I don't know what the differences are or how to tell by looking.

They are normally stamped on the head above the right-hand exhaust rocker cover. Mk2 should be RH10.

Tigernut said:

Thanks for all the info so far. Next thing to ask is about the heads - I see RH4 and RH10 listed but I don't know what the differences are or how to tell by looking.

Click to expand...

The Mk2 and Mk2A 850 got the RH10 cylinder head, the Mk1 and Mk1A 850 got the RH4 as did the Mk3 850.

The RH4 and RH10 are basically the same head with the exception of the inlet port entrance which is 32 mm on the RH4 and 30 mm on the RH10.
Due to that they have their own inlet manifolds to suit, 32mm to 32mm for the RH4 and 32mm to 30mm for the RH10.

Tigernut said:

Just bought (but not actually collected, so can't look at more than the photos) an 850 Commando. The frame plate gives date of manufacture as 12/73. The frame and engine numbers are 312329. It was originally sold in Canada. It has the perforated metal air filter cover and reverse cone silencers, roadster tank & side panels and the taillight with the large rectangular lens (same as T140s, T160s etc).

Is it a MkII? Furthermore, what practical differences are there between the 80 MkIs/IAs and the MkIIs/IIAs? I've gained the impression that the MkIIAs were de-tuned in comparison to the MkIIs (or was it the MkIs?)

Click to expand...

Welsh plugs in the swingarm? Beefed up swing arm? I have 3 850's, all 6-74 manufacture, ham can air filter. All RH10 head. No plastic air box. Inspection holes for rear brake. Original exhaust pipes were cross over. SN 612050 on the earliest one. Anyway WTF?