Engine number

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MikeM

MikeM

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I know this has been asked before, but I just noticed the prefix on my engine
20M3S and then 150649
I am pretty sure I have a 71 but what is the 20M3S designation. MK what?
I sent off for the despatch papers and they tell me it is an SS
Any further info?
What exactly do I have here.
Thanks
 
Early Commandos with the points housing behind the cylinders were prefixed '20M3'.

20M3S basically means camshaft points engine. The prefix was dropped from engine number 200000.

MikeM said:
I sent off for the despatch papers and they tell me it is an SS
Any further info?
What exactly do I have here.
Click to expand...

Then that's what it is as there was only one model of 750SS.
 
MikeM said:
I know this has been asked before, but I just noticed the prefix on my engine
20M3S and then 150649
I am pretty sure I have a 71 but what is the 20M3S designation. MK what?
Click to expand...

From FB the other day.

The 20M3 designates "Model 20" - the code for the 750 Atlas motor, going back to the AMC days and "M3" - the code for Mk 3, all together, the official engine designator for the Commando as it was introduced. The "S" added was the modification that moved the tach inboard with points on the end of the tach drive (among others).
 
Time Warp said:
From FB the other day.

The 20M3 designates "Model 20" - the code for the 750 Atlas motor, going back to the AMC days and "M3" - the code for Mk 3, all together, the official engine designator for the Commando as it was introduced. The "S" added was the modification that moved the tach inboard with points on the end of the tach drive (among others).
Click to expand...

Wondering about the 20 designation of the NHT. It is the first NHT with rearward moved bore (desaxe) to increase the size. It ran for 7 years (62-68) almost unchanged. However, what was the undocumented 20MK2 ? Atlas going to no spigot? High pressure oiling? Atlas Hybids ?

Then of course, as we know the 20MK3 is first series of commando.
20M3S is only a little over 1 years worth before the 200000 series which is the end of 750 NHT.
All of commando ran 8 years but with tons of changes. I only count 76 & 77 as late release 75's.
 
MikeM said:
I sent off for the dispatch papers and they tell me it is an SS
Any further info?
What exactly do I have here.
Thanks
Click to expand...

If they say that, you have one of these.

https://www.justbikes.com.au/motorcycles-for-sale/1971-norton-commando-750ss/JBW5064155

I probably clipped that quote a bit short (since it was written by someone else)

20M3S had come up a bit on FB in the last week, including the enthralling subject of power sockets along with pictures of a NOS metal body power socket and most likely only fitted to the 1971 (20M3S) year bikes.

Engine number


Engine number


Engine number
 
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LAB
I had posted in that thread, but had not seen (or did not rememeber) that tidbit on the 20MK2.

My first 20/slimline is a plain 63, then a 66 (only year for 389/689), plus another spare 66 frame waiting for a job and a 68 dunstall that started as a plain 20M2 and then left Dunstall with 32mm concentrics/rear points and a bunch of other goodies..

Certainly more time for the 20M3S than I had guessed. Was the 20M3 really that short in production? ... even the "R" stopped by early 69?
I've got 2 of those 20M3 motors
 
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dynodave said:
Certainly more time for the 20M3S than I had guessed. Was the 20M3 really that short in production?
Click to expand...

The Fastback supposedly continued as 20M3 until engine number 133668 late 1969.

dynodave said:
even the "R" stopped by early 69?
Click to expand...

Well, the 'R' wasn't introduced until early '69 (from eng. *129928*) and ended (approx. early 1970) at *135885*. The 'R' type supposedly having the 20M3 engine although I don't know if that applied to all?

https://www.nortonownersclub.org/models/commando
"R Type"

*(Numbers from Joe Seifert/AN if I remember correctly?)
 
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So is there a fair amount of 20M3 and 20M3S overlap? a couple thousand in the 131xxx to 133xxx area? More?

inoa sez first "named " fastback (69) 131180 should still be 20M3 and fastback oil tank? 1969 fastback 133668 first with 20M3S
 
dynodave said:
So is there a fair amount of 20M3 and 20M3S overlap? a couple thousand in the 131xxx to 133xxx area? More?

inoa sez first "named " fastback (69) 131180 should still be 20M3 and fastback oil tank? 1969 fastback 133668 first with 20M3S
Click to expand...

'S' type production (therefore first 20M3S) supposedly commenced from 131257 and what was then known as the 'Fastback' 20M3 ended at 133668 so it would appear the numbers in between could've been built as either '20M3' or '20M3S' although I'd expect there would have been batches of each but that's uncertain.
End of 20M3 'R' type I think, remains unknown but then not very many 'R' types were built.
 
L.A.B. said:
'S' type production (therefore first 20M3S) supposedly commenced from 131257 and what was then known as the 'Fastback' 20M3 ended at 133668 so it would appear the numbers in between could've been built as either '20M3' or '20M3S' although I'd expect there would have been batches of each but that's uncertain.
End of 20M3 'R' type I think, remains unknown but then not very many 'R' types were built.
Click to expand...

Yes
very likely that the roadster look was appealing and the newer 70 "roadster" (my first new commando) was envisioned to be released soon, they possibly no longer pushed the "R" which may have gotten some later 20M3S engines (per NOC). The 70 "Roadster" was series one rolling chasssis, halo headlight and 20M3S. I am hoping to put one together in yellow like my original bike.:D I am currently working on a 6205 bearing front end conversion for the Series 1 type frame
 
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Time Warp said:
20M3S had come up a bit on FB in the last week, including the enthralling subject of power sockets along with pictures of a NOS metal body power socket and most likely only fitted to the 1971 (20M3S) year bikes.
View attachment 12166
Click to expand...

I do find these 06-2099 on 71's, yet they had the roadster tank and mount which 'could' accommodate the later outlet. All my 72 have the later/smaller black plastic 06-2666 power outlet. No knowledge of consistancy during 71?....
 
dynodave said:
I do find these 06-2099 on 71's, yet they had the roadster tank and mount which 'could' accommodate the later outlet. All my 72 have the later/smaller black plastic 06-2666 power outlet. No knowledge of consistancy during 71?....
Click to expand...

DD the socket is actually the Bob plug according to FB.
From what I can gather, 1971 was the first year for the power socket and it seems the only year that it was metal (with a fine wrinkle black type finish) going to the rubber version in 1972 based on your reply.
The one in the picture I bought locally for my 71 Fastback for $40 (US$28) at the time, it seems it is quite a rare piece to find let alone new in the box.

All I know about the 20M3S is the stamping location for whatever reason moved from the curved part of the case to the flat area rearward sometime in mid or later 1971.

Maybe the guy who did the super neat stamping on the curved portion of the case retired in early 1971 so they moved to the flat surface.

MAR71 FB.
Engine number


A member here I hope.
Having read several posts about the 2 Pin Socket on the Commando I thought owners might find this interesting. I was at a Norton Owners Club meeting at Comerfords Motorcycle shop in Surrey UK in the late 1960's and John Hudson from Norton was there talking about development of the Commando. After the talk he asked if anyone had any suggestions for the bike. I told him that I had put a Power Take Off socket on my 650ss that I owned at the time. He took a note of this and said it was a useful idea that he would take back to the Factory, the socket subsequently appeared on the Commando. Therefore I can claim to be the originator of this and it is definitely there for 12V output and/or charging the Battery.
Click to expand...

I of course asked Bob what he used the plug for and he said a tent light.
A great story.
Paging Mr Frank Damp....
 
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I see from Jimbo's picture the stamping had been further forward again early in the piece (20M3) and slowly moved rearward over the next 5 years.
 
If I have a power socket, where is it located? I can say I have not seen one of these on my bike.




Time Warp said:
If they say that, you have one of these.

https://www.justbikes.com.au/motorcycles-for-sale/1971-norton-commando-750ss/JBW5064155

I probably clipped that quote a bit short (since it was written by someone else)

20M3S had come up a bit on FB in the last week, including the enthralling subject of power sockets along with pictures of a NOS metal body power socket and most likely only fitted to the 1971 (20M3S) year bikes.

View attachment 12166

View attachment 12164

View attachment 12165
Click to expand...
 
Previous rider may have removed it , I took mine off a long time ago ( don't like shaving ) .... think mine was on right side near mid ship ....
 
MikeM said:
If I have a power socket, where is it located? I can say I have not seen one of these on my bike.
Click to expand...

On the 71, they started on the air cleaner front panel. The power socket eventually (72 ? ) moved to the roadster oil tank /battery mount and moved to the two holes on the right side front frame mount bracket with the later style socket referenced earlier in the thread. red/brown-blue wire
 
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