JAXAshby wrote:
dave, nice explanation of how an oil pump would fail to provide any oil at all,
let alone pressure oil, to even the first bearing in line upon engine startup.

think of the grinding, clashing, rubbing, clattering you would hear on the
bearing for a minute or two or five.

Thus the old practice of chucking a rod with appropriate gear on the end
in a drill motor, pulling the distributor, and spinning up the oil pump
on older engines after a rebuild.

A bit out of my field, but I believe most of the noise I have
encountered with engines at startup (at least those that haven't been
sitting too long) is top end noise (vice more expensive bottom end
issues) and usually associated with hydraulic lifters pumping up vice
bearing issues. Recall that there is a fair amount of oil retention in
the bearings for extended periods of time, and the separation of the
journal from the bearing on oil during operation is based on pressure
developed by the rotating journal, not the oil pump. I believe the pump
sustains the quantity of oil and therefore only indirectly the thickness
of the oil wedge supporting the journal. My college machine design notes
and textbooks are in the basement and I don't really want to go dig them
out, but I believe my recollection is accurate.

dave

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