I have a 1940 WM20 fitted with a post war primary chaincase. I was going to replace it with,
what I believed to be the correct wartime one. However, when I offer the new chaincase up the clutch
cover dome fouls on the chaincase. Does anyone know if there are two wartime styles of cover with
different depths of clutch "bulge"? TIA Chris

email (option): chrisharrison45@yahoo.co.uk

The C Series covers (C10/11 etc.) have a shallower clutch dome as the clutch used is not so wide..It's quite noticeable visually if you place your post war one and the other one side by side....Ian

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

Thanks Ian, that explains it, as you say a noticeable difference. Post war one back on then until I find a war time one. Chris

email (option): chrisharrison45@yahoo.co.uk

An easy mistake which I've made in the past myself :laughing:....I remember I got all excited when I bought a NOS cover at a jumble only to find the same thing when I tried to fit it..From memory I think the level plug is in a different position as well isn't it?....Ian:relaxed:

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

There is also an M group outer chain case which was for the pre war M group with the 6 spring clutch. This also has the shallower dome but otherwise is exactly the same as a WD M20 outer chain case.

email (option): leonhop3_at_planet_dot_nl

A recent discussion has made me think about chain cases on the WB30, the outer appears to be the same on a WM20 WB29 & WB30 but the inner has a different part number.

So how is a B29/B30 inner cover different to an M20?

Outer
1940 "C" 29-8052
1940 M23 66-7525
1940 B29 M20 66-7502
WM20 66-7502
WB29 WB30 66-7502

Inner
1940 "C" 29-8054
1940 B29 66-7578
1940 M20 M23 66-7601
WM20 66-7601
WB30 66-7578

email (option): robmiller11(a)yahoo.co.uk

The chainguard fixing on the back of the case is at a different angle due to the different frame....Try checking the post war (46/47) inner chaincase number for rigid B Models to see if that is the same as they used essentially the same rear frame section...Ian

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

Rob a correction to your probable typo. The WB30 inner chaincase is 65-7578 and is listed in the 1947 parts list as being also fitted to the B31-32-33-34. Ron

email (option): ronpier@talk21.com

Thanks Ron...Ian

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

email (option): robmiller11(a)yahoo.co.uk

I've come across these multitude of similar but different BSA chaincases in the past.

I've got this pair of heavily painted cases that came with my B30 project and I'd like to check them out before I spend too much time on them.

Can anyone give me a clue where to look for the part numbers? So far I haven't seen anywhere to start looking.:mag_right:

Any pictures of yours Danny? Ron

email (option): ronpier@talk21.com

PS I've found the number on the outer 66-7503 which seems to be the usual BSA way on being one number out (66-7502). I guess for a part before it is finished?

Still looking for the inner number. Ron

email (option): ronpier@talk21.com

Had a look at the ones put by for my GPO WM20 and WB30 and Ian is right its the rear chain guard mount which differs.

Left marked 65-7578 Right 66-7602

Rob

email (option): robmiller11(a)yahoo.co.uk

66-7525 was the outer cover on 1940 M23 and 1939 M23 M24, how did it differ from 66-7502 M20 & M21?

Is that the version with the shallow clutch dome?

Rob

email (option): robmiller11(a)yahoo.co.uk