In a message dated 96-10-14 21:35:52 EDT, RJohn50603 (R. Johnson - Dallas)
writes:
<< If the relief valve looks OK, I would suspect that you have simply got too
much oil up in the upper engine and not in the pan at high RPM. Assuming that
your oil return passages are open and clean, some surgery might be in order
to increase the oil pan capacity. .....
..... I'd increase the pickup height to about 1/4" from the pan bottom to
make sure you're not starving the pump.
By the way, are you turning 7,000 RPM with no modifications to the bottom
end of the engine? If so, have you done this very often? Any problem with
"valve float"? Any signs of piston dents on the underside of the bonnet? >>
Seems to be about as many votes for oil stored in the upper engine as all
other guesses combined. It also sounds plausible, except that it has never
happened before (not that I recall), and I don't think my driving habits have
changed recently. So far I'm not convinced that this is the problem, but I
have a burning desire to know the oil level in the pan when the engine is
running at speed. I bet there are a few more of you that would like to know
as well. Maybe a sight glass mounted to the side of the oil pan is in order
here. By the dip stick the oil level at the MAX mark is 2-1/2" from the
bottom of the pan. Does anyone have a ready source for a 3" sight glass?
I don't like the idea of oil pan sugury. If the pumping volume exceeds to
run back volume, there will always be a some point where the pan will get
empty. If the oil is not running back fast enough I need to increase the
drain back flow capacity, presumably by opening up the holes in the head
around the pushrods. Where else could the engine store that much oil but in
the valve cover? And how long would it take? Does anyone know the flow
volume of the oil pump?
I will have the pan off again soon to refresh the rod bearings, will be
checking the oil pump over again very thoroughly, as well as the pickup
screen and pickup tube. I will be paying close attention to the height of
the puckup tube, lest it be too close to the bottom of the pan. I will
probably dent the bottom of the pan downwards about 1/4" under the pickup
tube just to be sure. Does anyone know if it is possible for an otherwise
normal oil pump to cavitate without sucking air? I know a lot of racing
engines run faster than my stock engine, and I can't recall ever hearing of
oil pump cavitation.
Yes I run it at 7000 rpm sometimes (OK pretty often) with no modifications to
the bottom end. No problem with the valve float, it occurs naturally at
about 7400 rpm as near as I can read my tach. It makes a really loud raspy
sound out the exhaust, must sound like all hell breaking loose because I have
seen many a track worker dodge for cover when I pass. Doesn't seem to do any
damage to the engine. The sturdy little bugger gets into valve float several
times a month (OK maybe more), and has been able to get about two years out
of a set of rod bearings. People occasionally suggest stronger valve
springs, but there's no way I want a stock bottom end doing 9000 rpm! (No
anatomy jokes please.) So far no sign of piston dents. Do they look
anything like fan blade dents?
Barney Gaylord -- 1958 MGA
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