Engine Numbers

Stephen Hill · Jan 4, 2025

I recently acquired two sets of Norton engine cases, two of which have numbers stamped on them that leaves me puzzled.
Stamped on the front of the drive side engine case is 20121777P
Stamped on the upper side of the drive side engine case is 20/114656/P
Both have the small breather elbow on the left end of the cam tunnel
Any ideas on year, model, displacement?
Stephen Hill

marinatlas · Jan 5, 2025

A

Thread 'What model from crankcase serial #?'

Nov 28, 2016

Does anyone have info on what model Norton would have the crankcase serial # 20 1254xx P?

Thanks,
Ed

Interbak · Jan 5, 2025

The 20 means they are 750 Atlas, the P means built at the Plumstead factory.

Stephen Hill · Jan 5, 2025

Thanks guys.

Beardown123 · Sep 20, 2025

Stephen Hill said:
I recently acquired two sets of Norton engine cases, two of which have numbers stamped on them that leaves me puzzled.
Stamped on the front of the drive side engine case is 20121777P
Stamped on the upper side of the drive side engine case is 20/114656/P
Both have the small breather elbow on the left end of the cam tunnel
Any ideas on year, model, displacement?
Stephen Hill

Hi Stephen,
20/114656/P suggests a 750 Commando from around 1972-73.
20121777P looks non-standard—possibly a factory replacement case.
The small breather elbow fits early 750 models.

L.A.B. · Sep 20, 2025

Beardown123 said:
20/114656/P suggests a 750 Commando from around 1972-73.

I don't know where you have got that information from but it's obviously wrong as '1972' started from 200000 and '1973' started from 212278.

20/ is Atlas.

Engine Numbers

Stephen Hill

marinatlas

Thread 'What model from crankcase serial #?'

Interbak

Stephen Hill

Beardown123

L.A.B.

Moderator

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