There's a confident N15CS expert out there on FB, watch out!

Facebook guy comments on an obvious N15CS and says that it's Commando engine, Atlas engine cases different from N15CS. Learn something new every day .

gpzkat said:

Facebook guy comments on an obvious N15CS and says that it's Commando engine, Atlas engine cases different from N15CS. Learn something new every day .

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I have seen an item advertised (9 Nov 2025) in uk on fb marketplace. I was interested in this bike but was put off by the Commando reference but am not familiar enough with the Atlas/N11/N15 engines. I can see that some engines have an external feed to the rocker box but I don't know which engine should have what feaures. Similar questions about the crankcases. Could you explain the differences that I should be looking for please?

I'm no expert, but there are threads on this forum detailing the differences between the cases. The N15CS uses a Matchless primary, and there are evidently machining differences. The case part #s are different (25374 vs 25375), maybe due to that. I don't think they are visible externally.

My point was more chronological; the N15CS preceded the Commando, so how could it have a Commando engine?

My G15 case only appears to be different from my Atlas because of an aluminum spacer epoxied onto it as a spacer for aligning the primary.

gpzkat said:

The N15CS uses a Matchless primary, and there are evidently machining differences. The case part #s are different (25374 vs 25375), maybe due to that. I don't think they are visible externally.

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Threaded holes for fixing primary cover to the Commando engine are rotated 15 degrees (by memory!) CCW to the Matchless cases. Pattern is identical. Other than that, I don't see any differences and I have both of them. AMC used a galvanized steel spacer + gaskets for aligning the primary cases. For the Commando, a gasket only was used. This remark applies to the 1966-68 models ONLY.

- Knut

Thank you all. I'm minded to think that so far as the item that I have seen for sale is concerned, I would not be able to properly identify whether the parts are correct for it. I'll not pursue it any further. For anybody interested, it is here: N15 on fb

gpzkat said:

I'm no expert, but there are threads on this forum detailing the differences between the cases. The N15CS uses a Matchless primary, and there are evidently machining differences. The case part #s are different (25374 vs 25375), maybe due to that. I don't think they are visible externally.

My point was more chronological; the N15CS preceded the Commando, so how could it have a Commando engine?

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I was going to comment on noticing the external differences in the primary outer covers, but I think it might only apply to the P11 because the foot peg on that side has a mount point through the inner and outer primary covers.

Putting a Commando engine in a N15 frame is doable, but it isn't correct for a concourse restoration obviously. ludwig has a 850 in a N15 I think. Anywho, it sounds like the seller is confused, or needs to rewrite the ad for the bike he/she is selling. Saying the 750 engines are the same for an late pre-Commando and early Commando might be close to the truth if the heads are top oilers. I'm no Norton restoration guru though. Not even close.