Good reasoning, Classic Biker. The pulsing effect is normal for any two stage pump, as you say, that the return
volume has always to be larger than the supply volume. But these pulses come from the lowest point of the
crankcase, where a dry sump has to be maintained under any circumstance.
If you look at your splendid drawing above, you can see, that the feed hole has been designed in a stepped form, with reduced inlet bore to the larger collecting diameter. Widening the collecting cone would probably
easy feeding the pump, but widening the reduced diameter will possibly reduce the short moment of suction
by the piston of the pump which is needed to collect the oil around OP31- worm, which should be fed with
oil only, as on top of the reduced diameter should always be full oil coverage, so keeping up suction to the
collecting point in the crankcase and not adding air volume from a second point.
As this hole has been bored by a chosen drill during machining, I am convinced, that PEI put some thought
into it.
Somewhere in his books, he mentiones, that they used to have glass windows on the timing cover, to observe
the lubrication process on this side of the engine, when they eventually observed sparks with MKII cams at
the time.
If there is too much air in the return line, not only too much oil remains in the engine, so producing overheating, but also at some time an overflooding in the drysump, when the engine starts oiling
at a very sudden for seemingly no visible reason. Worn cams and spindles not only result from wrong
positioned feed holes in the spindles, but from some other reasons, too.
My starting question related to many complaints in MPH about the pilgrim pump, PEI was not
amused about, writing a comment in MPH or somewhere else - which I do not remember, as it is too long ago -
where he listed feed rates and pressure figures of other oil pumps in contemporian engines, showing
competetive figures for the chosen design. This pump is more than sufficient for both Vincent engines:
Twins and Singles. The oiltank is very effective as an oilcooler, visible during winter, when it is difficult
below zero degree figures, to achieve operating temperatures, asking for stuffing the airspace between oiltank and fueltank.
All said only for the original design. Irving Engines are a different matter.