Engine number
- Thread starter MikeM
- Start date
- Status
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.
Then that's what it is as there was only one model of 750SS.
20M3S basically means camshaft points engine. The prefix was dropped from engine number 200000.
Then that's what it is as there was only one model of 750SS.
Time Warp
.......back to the 70's.
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).
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.
From March '69 (750 S type) to (sometime around) the end of '71?
Time Warp
.......back to the 70's.
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.
Last edited:
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
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
Last edited:
The Fastback supposedly continued as 20M3 until engine number 133668 late 1969.
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?)
Last edited:
'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.
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.
I am currently working on a 6205 bearing front end conversion for the Series 1 type frame
Last edited:
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?....
Time Warp
.......back to the 70's.
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.
A member here I hope.
I of course asked Bob what he used the plug for and he said a tent light.
A great story.
Paging Mr Frank Damp....
Last edited:
If I have a power socket, where is it located? I can say I have not seen one of these on my bike.
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
- Status
Similar threads
