No doubt this question has been asked before, but when a WM20 left the production line did the engine and frame numbers match exactly? Any other BSA's that I have that I've got checked out by the BSA owners club (two B31's and a C10) have the origional engine and frame that they left the factory with but the numbers do not match exactly number for number. Eg. frame number in the B31 could be XB31 12347 while engine number could be XB31 12548.

email (option): glenn_mullan@postmaster.co.uk

hi glen, very rarely did they match, some of the early contracts did, but not many that i've seen, and as soon as they went to a base workshop things got well messed up .

email (option): chris.astinbarker@btinternet.com

BSA often used one frame for more models like the XB31 frame could also have an XB33 engine. For every XB33 engine fitted to an XB31 frame the numbers started to differ more from the XB31 engine numbers.

Most military M20's had matching numbers, a few of the early M20's had different engine and frame numbers but soon during the war all had matching numbers. In the frame number page you can see that quite a few M20's survived still with their original matching engine.

Henk.

email (option): ahum@quicknet.nl

I noticed that, that's what got me thinking as I have never seen BSA do that with any other model other than the M20, though I'm no expert on BSA's by any means. It must be something when your original engine turns up on the other side of the world. What a story it could tell!

email (option): Frame & Engine Numbers

Although not all WD manufacturers did it, there seems to have been some sort of WD pressure to build with 'matching' numbers - all it probably meant was that engine and frame numbers were stamped in the despatch department.

Nortons had completely different numbers pre-war and changed to matched numbers at W1000 in September 1939. They never lost the habit and started at 1000 again in 1946.

It's quite possible that the Ministry of Supply was responsible for this whole matching numbers nonsense that afflicts the world of classic motorcycles.

On the pre-war scene, owners are happy with an engine from the same model year as only someone with the factory records could spot the replacement.

My personal feeling is that it's nice to have engine and frame from the same year as it makes the choice of specification easier. Most WD bikes of course should be displaying 'rebuild' census numbers.