Re: datation M20 cadre et moteur, Census Number et historique,
Bonjour François,
Voici quelques infos sur ta BSA. Je vais continuer en Anglais, comme c'est la langue de ce forum.
Your WM20 with frame number WM20.83956 comes from contract S/1048. This was a contract for 15.000 bikes, ordered in September 1942. Production started in early June 1943, and in that period they were producing almost 2.000 bikes per month. This means that your bike must have been assembled in July 1943. It would have had the census number C5117356 on the tank. Here are some other WM20s from the same contract being pushed out of the factory. These bikes must have been assembled approximately two months after your bike.
Your WM20 engine with duplicated frame number WM20.27399 comes from contract C/7287. This was a contract for 17.000 bikes, ordered in May 1940. Production started towards the end of August 1940. Your bike (your engine to be precise) was despatched from the factory on October 4th 1940. It would have had the census number C4343991 on the tank. Here is an WM20 from the same contract, despatched from the factory on September 27th 1940.