In a message dated 96-10-13 21:38:19 EDT, dondaves@ix.netcom.com (Don Daves)
writes:
<< How about the possibility that the oil pan was pumped dry? ..... My 69
Ranchero with 428 engine was rebuilt with a hi-volumne oil pump. The rocker
shafts were a little worn, allowing the excess oil flow to fill both valve
covers - the oil couldn't get back to the pan fast enough and, as the pan
emptied, the pressure would drop to zero at high revs, then at idle, the
pressure came instantly back to normal. The simple fix was to run about 1.5
to 2 quarts additional oil in the crankcase - not enough to get splashed by
the crank, since probably 2 quarts are always circulating through the engine
whenever it's running. It did solve the loss of oil pressure and still runs
great after 50,000 miles or so.
Another thought is that maybe the oil pick-up is a little too high and not
reaching all the way to the bottom of the pan.
In both cases, I think that adding one extra quart of oil shouldn't hurt
anything (we're only looking at maybe an extra inch of level in the pan) and
if you don't lose pressure again at 6,000 rpm, you've found your problem. >>
This suggestion scares me a bit. I'm pretty sure that in an MGA there's not
enough room for another 2 quarts between the full mark and the bottom of the
crankshaft. If the crankshaft touches the oil I would imagine instant
foaming to occur, and I don't like the idea of air bubbles being pumped
through the bearings. Anybody know if you can overfill the oil in an MGA
without problems?
I think the rocker bushes are OK. With the new crank and bearings it put up
50 psi oil pressure at 800 rpm idle. I did have loose rocker bushes in the
past, and when I renewed them the oil pressure went from 20 to 50 at idle.
The oil pan is still flat on the bottom, and the oil pickup screen is very
close to the pan. In fact the bottom inside of the pan has some scuff marks
that match the shape of the pickup screen, so it must be really close. The
pickup tube is also very close to the bottom of the screen, like within 1/8
inch, but definitely not touching. The end of the tube also has two small
notches on opposite sides, presumably to allow oil entry even if the pan gets
dinged up against the tube.
I'm feeling gutsy today, and I feel the need to test the drain back theory.
First I'm going to replace the rod bearings again. Then as a test I'm going
to run it at a steady 7000 rpm for a half minute to see if the pressure goes
away. If it does, does anyone have an idea on how to rig up an oil level
sensor in the oil pan?
Barney Gaylord -- 1958 MGA
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