I have a cracked outer gearbox cover 66-3103. I have seen some 66-3102s for sale. Are they compatible/straight swap over? Would anyone have a decent cover for sale please? For a 1945 WM20. Many thanks.

email (option): geoff.turner@hotmail.co.uk

I don't know the answer to your question but Dave Plumb did a great job on welding my cover a few years ago.

One of those 2 numbers is not a part number
One is the casting number & the other is the actual finished part number

I guess all wd gear box covers are the same ?
Except the early models had a ring for a dust cover on the clutch arm ?

The number 66-3103 is the number cast inside the cover. So this would be the same as part number 66-3102?

Mine has the same number cast inside.

email (option): pes.sales@btconnect.com

yes
BSA borrowed every penny needed for each years production ( Tax avaoidance scheme ) and the money was guaranteed agains goods in production
Thus every part had to be accounted for thus every raw casting or forging got a part number because it had les value than a finished part .
Usually they are 1 or 2 digits different
You will see the same with the head, primary cover ( both sides ) and a lot of other parts
Now because a lot of different parts were made form the same castings / forgings having the same raw product number does not mean the part has been machined to fit your bike so it can be a little trap when sifting through auto jumble prts .
In the technical section there is a good write up on identifing gear box castings .

Welding the gearbox boss is not an easy job and I got mixed results with the ones I sent to Dave..I think from memory I scrapped two of them as it was impossible clean up the boss true and to the correct size for the bush after welding...Subsequent to that I made a jig for holding the cover in the lathe, machined the boss down on the inside and fitted a steel support ring rather than welding...You can see the steel ring after fitting in the picture below...Ian

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