Here's Rons WB30 timing cover with the early pattern (pre 48) BSA script and breather assembly...Despite the late B30s having a total of 4 breathers (2 flap valve breathers, 2 plain breathers) the post war B31, which was a direct developement of the B30, had only one and it wasn't in the timing cover!!..However, it returned to that location in 1948 and remained there on SV and OHV types until the last M21s were produced in 1963...Ian

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

I can't help with the part numbers as mine tend to get updated as knowledge improves.
Don't think my face mounted O-ring caps are like any other, they are very good at staying put. They were designed that way.
As for your slotted caps, do you mean these? If so they have been made.

Mark

email (option): pes.sales@btconnect.com

BEcause air has mass there fore it also has inertia
So the movement of the air inside the crankcase lags behind the piston movement as the revs increase to the point that it becomes 100% out of phase with the piston movement and then there is resonance of the flapper valve on simple M series types and an even bigger problem with spring loaded cheack valves .
The original flapper was OK when engines had no oil seals were long stroked and reved to 4000 rpm flat out
Add to that most had very heavy flywheels so they accelerated slowly.
As strokes shortened , flywheels got lighter , engines accelerated faster, crankcases became sealed ( sort of ) the flow of air bcame a big problem
More splash allowed way too much oil to pass through the breathers .
Thus it was found necessary to move them, modify the acual outlet hole and it's orientation within the crank case

When Rex Bunn did the original research which led to the Bunn Breathers he found that very little actual published research had been done on single cylinder crank case breathing

Thus HD & RE now use a system he designed
Now when it comes to splash and oil flow inside a crankcase it was and largely still is guess work .
The Aukland University actually did a Bert Hopewood and fitted some crankcases with windows and cameras to try & verify theories of internal oil flow
When we tried fitting a flow through system to A 65's it was a major problem trying to place the outlet where it did not take 3/4 of the oil flow to the head with it but the A 50, essentially the same engine worked fine .