The Gold Star had the flapper valve replaced with a mechanically driven, timed breather when maximum revs on late models got to more or less 7,000rpm....
At speeds of approx.. 6500-7000rpm the flapper valve ceased to know which direction it was supposed to be going in...M Series engines, the B Series B31/33 models and early Goldies coped OK with the flapper valve in place....
In my experience engines have a tendency to blow a little oil from the breather straight after a rebuild, or more specifically a rebore....After around 200-250 miles this tends to stop as the bore/rings become 'bedded in'...
Wet sumping aside the breather should pass little oil under normal use...For example, I completed a 2,600 mile trip on my 1951 B33 and didn't have to put in any oil, though the level in the tank had dropped a little...Approx. 900 miles of that was motorway driving at around 60mph...
I've done 1000 mile plus trips on the M20 on many occasions and also not had to use any additional oil...
The 600cc tuned B33s I have built that produce maximum power at approx. 5,850 rpm have also all run on the standard breather...The only one I did have problems with regarding leaks/excessive oil from the breather was my 720cc B33 and I suspect that was an air volume issue...The addition of a second flap valve resolved that...Ian
