Found the quill feed broken off of the timing cover on my spare engine , but to my amazement and luck, have 2 spare timing covers, both with a good quill
However, there are subtle variations- on the left, the cover with the broken quill has a knobby casting on the bottom, and no part number cast inside.
In the middle, same knobby casting but an unreadable casting number. And on the right, probably the earliest, is a clear casting number. The engine has a 100000 range serial number, so when did they change over the casting to include the additional boss (assuming it is there for some OHV application?
All have the plain BSA on the round part, not the later winged script.
Are they all interchangeable?

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email (option): vinver@ns.sympatico-dot-ca

Hi Vincent, very good question.

The lump you mention is an unfinished breather.

It would seem that some B30s were using this breather during the war but I'm not sure in which year this started.

Several contracts of M20s from around 1942 were originally ordered as B30s before the government had a change of mind and decided to stick with the sidevalve. But its quite possible that tooling had already been started and moulds for some parts had already been made, then perhaps as the original non breather moulds wore out they used these instead of making more.

But this is mostly guess work.

Rob

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

Hi,
my side cover doesn't have the lump as mentioned before by Rob.
Does anybody know anything about that ?

Rob's theory is very plausible..An order for 10,000 B30s was placed but subsequently cancelled and altered to M20s...
BSA were geared up to an extent for B30 production and did produce one complete batch and one partially completed batch, so a full set of casting patterns were in use....

However,of the two basic B30 variants only the later one had the breather in the timing cover...I have a full set of factory drawings for the B30 engine covering the early and later types and a further 'intermediate' engine that shared features from both...From these and other information I have it may be possible to date the introduction of the breather...
If B30 cover castings were used then any M20 from approx. 1941 onwards could have had one of these fitted with the breather hole left unmachined...
Additionally they could have been fitted post war as replacement parts, coming from the B30s descendent, the B31, which also used this type of cover up to 1947...That alone seems unlikely though, due to the high number of covers that turn up...

Anther possibility, which I don't know the answer to,...was this type of cover fitted to late 1930s OHV models as well?..

From a practical point of view if you want the 'plain' casing the external 'lumps' can simply be filed off to leave you with a visually 'M20' cover..In all other respects they are the same...Ian

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

Hey Vince,

That quill should be repairable.
If you don't want that cover, I'd like to get it from you.

Cheers,

Robb

email (option): britool51@hotmail.com

A WB 30 without the timing cover breather.

and one from a later contract with bigger front brake and timing case breather


Ron

email (option): ronpier@talk21.com

The 'breather question' is an interesting one as BSA obviously had problems with determining which was the best location for it, how many there should be and the exact specification...
Pre war OHV models and M20/21s from about 37/38 had it either from the main bearing housing or just below the cylinder on the drive side, at the top of the crankcase..This varied over the model range....All wartime M20s had it in the latter location, as did the B29 and first version of the B30.
On this first B30 the breather was further supplemented by two additional, 'non valved' breathers in the rocker covers...
The second version of the B30 then had the breather added to the timing cover whilst retaining all the others, giving it the odd distinction of being the only BSA with four breathers!...
Post war the B31 arrived which was a further development of the B30 engine...
This now had just one breather located back on the main bearing housing on the drive side...
In 1948 it was moved again back to the timing cover where detail modifications were made three times to the breather pipe and cover to prevent excessive oil loss..
Additionally, although the sizes of the tufnol flap valve remained unaltered there were three versions of the housing that located it into the breather body, which altered its performance in terms of air capacity....
It is probable a 'one size fits all' crankcase breather wasn't possible throughout a range of engines that were broadly based on one crankcase assembly but varied from pre war M24s through the sidevalve range and iron OHV sports models right up to the last Gold Star in 1963....(which by then had a mechanically driven breather).....
Equally it seems BSA had a fair bit of trouble sorting out the best set up for each type, particularly the OHV models...Ian

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