B31 Engine and Frame Number Mystery

[Paul Andre de la Porte]

Greetings! One of my neighbours has an old B31 that has been holed up for quite a lot of years. The previous owner who is now deceased is reported to have acquired it towards 1976 from a junkyard or derelict bike shop in the flea market in Tunis, Tunisia, and it is known to have been a police bike in its active days. I could be interested but it has no papers, and in order to license it I would at least need to have the engine number. It appears to be a 1955 to 1957 model. However, the left hand side of the engine casing where the number should be is totally void of any inscription save a vague and small circle, about 1/2 inch wide, which however looks pretty authentic. No signs of any filing or erasure efforts either. The frame number on the stock head says CB 31 ....., clearly there have been numbers after that but they are illegible. The bike is covered in grime, so my question is: is there a possibility that police fleet bikes could have had their identity numbers stamped on somewhere else than on the left hand engine casing? Surely the engine would have to be identified somehow? Any insights will be greatly appreciated.

[Spaceman]

My ex-police B40 has the frame and engine numbers stamped in the normal places. In the UK, its the frame number that matters most and defines the identity of the bike like a modern VIN number - it does need an engine number but that does not have to be the one originally fitted to the bike because engines do get changed.

[JulianS]

If there is no engine number, and it has not been ground off, then it is likely that the original crankcase was damaged and replace with a new unstamped one. Normal service practice would be for the replacing dealer to stamp the new case with the original number but often this did not happen.

[Paul Andre de la Porte]

Many thanks to both of you, very useful replies. I guess I'll have to investigate the frame number a bit more closely.