The pre-WWII singles with the breather on the primary side is generally plumbed as a chain oiler. Post WW II singles had the beather on the timing chest and it generally vents to the road.
If you are getting a lot of oil out of it then you have problems. The flapper valve really only works well up to 3000rpm. From there on it gets less and less effective till eventually it ends up being totally out of phase with crankcase pressure. Spring loaded valves as fitted to some brake valves work better than the flappers at higher revs.
Most likely your rubber seals on the cam spindles need replacing and you are getting too much oil in your timing chest and thus too much oil in the breather. the next biggie is your rings are on the way out.
Thanks for the responses guys. The flapper valve is still in the breather fitting, and its shiny seats suggests it is moving about at least some times...
Trevor, the rubbers you speak of, I guess its these, circled in red?
They are nice and soft and fit the cups in the timing case nicely. Not tight, but a neat fit. What stops the quill that feeds the oil gallery in the timing case from leaking where it enters the hole circled in yellow? I can imagine oil spewing from here, taking the easy pathway rather than entering the galleries in the timing cover.. Is there a seal missing?
Last question: Why does the Draganfly catalog show a rubber seal on only one camshaft when it's obvious 2 are needed? Wrong drawing?
The rubbers should be a tight fit in the cover not on the nipples. The parts book only shows one seal but lists 2 in the quantity as they have the same part number. The quill is a tighter fit in the crank than it looks and there is no seal there. The other thing I forgot to mention is you pressure relief valve. It could be stuck open and allowing too much oil to bypass or the scavenge valve could be partially blocked also allowing a build up of oil in the sump.
I do not want to sound like I am spruking for them but the Bunn Breather kits do a really good job on B series engines, probably better than for the unit singles they were originally desgned for.
Hey Trevor, I got an email from Rex today. I'm going to try one more thing before I buy one.
The timing cover gasket had a piece missing where the red mark is in the pic below, so that would have been dumping a bit of excess oil into the timing case. So I'll fix that, reposition the hole in the breather pipe inside the timing case, replace the flapper valve and relocate the end of the vent hose to a more suitable location with a slash cut draft tube end and see if it's any different.. All good fun
I think the positioning of the hole in the breather has some effect on the amount of oil that gets thrown into it from the pinions etc. From a couple of timing covers that I have it appears BSA tried to address the problem with a different casting to shield the breather somewhat.
I was given a box of B31 etc bits recently which included a breather which had been modified in that a strip of metal had been bent over the pipe and soldered in place, so shielding the hole. Presumably whoever did it has also had problems. Cheers Pete