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.
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.
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
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
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
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.
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.
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.
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.