Michael,
An engine oil pump is a positive displacement pump which pumps its volume of
oil according to engine RPM's (i. e., five times as much oil at 5,000 RPM than
1,000 RPM). A liquid (engine oil, in this case) is not compressable. This set
of "givens" would be a problem if not for the very simple oil pressure relief
valve which controls the pressure via a spring. The valves purpose is to by-
pass excess oil that the bearings cannot use, otherwise the oil pressure would
go sky high on a tight engine at higher RPM's. 500 PSI of oil pressure is not
helpful to bearing life. In fact, at very high pressures the oil would begin
to erode the bearing material, not lubricate it. At certain flow rates, oil
viscosities, temperatures, RPM's the very simple, but effective valve can go
into a cyclic motion.
It does this just to perplex us and give us something to talk about. See, its
working right now.
An old rule of thumb is that you should have at least 10 PSI of oil presure
per 1,000 RPM of engine speed. I know that takes care of my MGB situation. How
about yours?
R. Johnson - Dallas
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