I’m sorting out my bits to start on this winter’s project and I seem to have accumulated 3 engines for one frame. One of the engines is lacking the breather on the drive side and has, instead, one in the timing chest as per B models. Is this correct or have I got some something weird going on here?
Cheers
Pete

IMG]http://i110.photobucket.com/albums/n120/pcomley/Motor1t.jpg[/IMG]


OK, now why don't my pictures pop up??

email (option): petercomley@web.de

Hi Pete

Its a ZM20 engine which would make it late 1940s civy and that I think is the correct timing cover for the engine.

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

Hi Pete, Engines up to and including 1947 had the breather on the drive side. For 1948 the breather was moved to the timing cover and deleted from the crankcase. At the same time the 'Winged' BSA logo was added to the cover to replace the earlier plain block script.
Later 'Z' type crankases, along with all subsequent ones, also had other detail changes made....Ian

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

there that should work
you have to put the letters IMG into lower case img and at the beginning it must have square brackets around it and at the end of the link it should have the square brackets around backslash img. Basic HTML

email (option): c.coxon@blueyonder.co.uk

Is having the breather on the timing side much of an improvement than on the drive side? I've read somewhere that someone has a breather on the timing side AND drive side to make an even better improvement, is that necessary?

Hi LJ, They seem to manage alright with one breather. The later WB30s had two as standard (the only bike thus equipped I think)but this was reduced to one on post war B31s. (on the early (46/7) B31s it was under the main bearing housing on the drive side.) The sidevalves and pre war OHV models (B29, M23/4 etc.) had it just below the barrel on the drive side.
When it was moved to the timing side there were problems initially with the breather passing too much oil. A sheet metal shroud was riveted to the inside of the cover to mask the end of the breather pipe. This was later cast as part of the cover. However this did not fully solve the problem so the next mod was to crimp the end of the breather pipe flat (inside the cover) and then a small hole was drilled through the side of the pipe. This seemed to do the trick and no further changes were made to the M and B Models.
The one exception was the later Gold Stars..at speeds over 7000 rpm the flap valve type breather could not operate fast enough. It was replaced by a timed mechanical breather on these models....Ian

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

Thanks folks!

email (option): petercomley@web.de

Hi Ian,

ah ha! I see... Thanks for taking the time to post that. I'm much clearer now. Cheers

Just for history sake, the m20 motor was fitted to a portable swing saw here in Australia in the 1950's made by a bloke named Alf Hargan(?) and were locally known as a Hargen Saw.
The M20 motor was laid flat on it's back and fitted with an attomiser flapper valve carby device. The breather hole in the timing cover was used to put a pipe in for the oil pump to suck the oil back to itself via an pipe welded to the sump plate and then on to the oil tank. The motor had a breather on the drive side also.
The motor in these saws were also run laying on their side with the timing gear cover facing the ground.
Mot bad for a M20.