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Re: M21 engine id

BSA had problems with the breathers I think...At various times they exited from the rear of the main bearing housing in the crank case, just below the barrel on the drive side and from the timing cover...The timing cover breather arrangements went through three different changes to reduce the amount of oil loss and there are two different versions of the internal breather flap valves...(and of course there's the timed breather on the late Gold Stars)...Not to mention the two different diameter vent pipes on SV and OHV engines...

The 'piece de resistance' had to be the late WB30, which had a breather in the crankcase, the timing cover and two additional 'non valved' breathers in the rocker covers!!....Ian

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

Re: M21 engine id

Is the JM the narrow frame and engine, if so shirley a wide engine wouldn't fit in??

Rob

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

Re: M21 engine id

Ron Pier
If the breather is on the timing side, it sounds like post war crankcases to me. Email me the pictures if you want and I'll add them in this thread. Ron
Pics emailed to Ron Pier.
It’s an interesting bike I think.

email (option): Marcus@glassenbury.plus.com

Re: M21 engine id

Rob Miller
Is the JM the narrow frame and engine, if so shirley a wide engine wouldn't fit in??

Rob
It can be fitted as I have done this with a JM frame and a post war M.21 engine. All you need is to add a couple of packers to the front down tube / rear frame between the engine plates and the rear frame. This enables the round tube to pass around the oil pump housing in the crankcases. Not ideal I admit but if you don't have a JM engine then it is a solution.

email (option): keithchandler@clistandchandler.co.uk

Re: M21 engine id

Yes Keith I already spotted the spacer on the front rail on Marcus's bike. Here are some pictures. The 39 Marcus referred to is the inspectors stamp. Ron
IMG-E1805
IMG-1878
IMG-1655
IMG-1877

email (option): ronpier@talk21.com

Re: M21 engine id

Have you checked the crank case half numbers on the engine plate boss at the front of the engine?...Ian

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

Re: M21 engine id

I have now seen the spacer where the front down tube meets bottom frame rails. I take a look at casing numbers but I am thinking they will not match.

email (option): Marcus@glassenbury.plus.com

Re: M21 engine id

That seems likely...It looks like you have the crank case halves from two different WD engines...
Unfortunately the correct engine you require, or parts off, aren't all that common, though not impossible to find....Virtually no internal parts from the timing side or the top half components are interchangeable between the two types....Ian

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

Re: M21 engine id

Actually not a bad combination to my mind. maintaining the character and engine number of a 1938 bike with the extra robustness and improvements of a later engine:+1: Ron

email (option): ronpier@talk21.com

Re: M21 engine id

There were no JM prefix 20 or 21 supplied to the War Office so it would perhaps be worhtwhile to ask the BSA OC or the VMCC where that engine went to.

The Inspection mark (is it 39 or 89 ?) will apply to the individual inspector rather than be a year indicator. Unlike many factories,where all the early-war engines were inspected, BSA seem to have only been subject to occasional controls. Does anyone else have a similar stamping ? These inspectors only seem to have stayed 6 months or so at each location. I can date early-war Nortons in this manner.

Re: M21 engine id

Inspector M89 stayed at the BSA factory in the (late) 1939 - (early) 1940 period. I have these examples in my Register:
KM20.1376, KC10.1779, WC10.552, WC10.583, WC10.720, WM20.11612.
The next one in my list is WM20.20576, with acceptance marking M^65.

More examples are always welcome! :grinning:

email (option): wd.register@gmail.com

Re: M21 engine id

So far as the bike is concerned I plan to keep it mostly as is ‘ex government’ trim. It appears to have been black since it’s wartime use except for the green tank panels which look to have been added later. I am quite happy with its current engine for now as it’s original engine JM23 159 is unlikely to be found or any JM23 engine for that matter. I may think about fitting a later B/M ohv engine one day.

email (option): Marcus@glassenbury.plus.com

Re: M21 engine id

Jan
Inspector M89 stayed at the BSA factory in the (late) 1939 - (early) 1940 period. I have these examples in my Register:
KM20.1376, KC10.1779, WC10.552, WC10.583, WC10.720, WM20.11612.
The next one in my list is WM20.20576, with acceptance marking M^65.

More examples are always welcome! :grinning:
I think it looks like M 39.
Any info ?

email (option): Marcus@glassenbury.plus.com

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