Good evening.

Is there a way that one can tell if an M20 magneto on a 1940 BSA is correct or post war?

If so what's the difference?

Regards,

Mark

email (option): towersmark84@yahoo.co.uk

They are dated on the plate (eg - "7/44") but it is unlikely that most WD bikes today will retain the original magneto as most were changed over at re-build/overhauls, etc...............

I believe 40s magnetos have a different "bed" where the dynamo lies in. Its longer than those of the 50's.

One other thing I forgot to mention about the small screwed-on identification plates is that the early ones, up to about 1942-43 are plain brass, then alloy (although this was used earlier) then post-war the alloy black/silver coloured type.............

Thanks guys! I will check it out 😃

Regards,

Mark

email (option): towersmark84@yahoo.co.uk

This is a photo which Clive Sammut sent me some time back.

Wartime on the left, post-war on the right.

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There are detail differences on some of the 1930s magdynos, particularly in terms of dates stamped direct on bodies and of course the pre-1937 scalloped end cover, but to all intents and purposes you can ignore those.

The main body casting is different on wartime mags to post war ones..

Where the dynamo sits on top of the mag the mag body has a curved 'seat' to locate the dynamo machined in its top face..

On wartime mags this seat runs under the entire length of the dynamo until it meets the rear face of the drive end gear housing...

On postwar mags this seat is abbreviated before it reaches the rear face of the drive end housing...This results in a 'waisted' appearance and a gap under the dynamo body for part of its length..

The pick up should be attached to the body of the mag on the opposite side to the cylinder and when viewing the contact breaker assembly end the adv/rtd cable should enter the mag to the right of the breaker assembly....Ian

email (option): ian@wright52.plus.com