Robert M. Simon wrote:
Still working on a very low oil pressure problem.  Pressure tested the
gauge and it is correct.  Startup is 45-50 psi, idle at 1,000 shows 40
psi at 110 F,  35 at 120 F, 30 at 130 F, 25 at 140 F.  In cruise it
stays at about 22 psi and 185-190 F.  On landing and pulled back to idle
pressure dromps quickly to 5 psi and if I do not goose it quickly, down
to 2 psi!   To get back to the hanger or for another TO I have to keep
the RPM at 1,000 and ride the brakes.  I screwed the pressure controller
all the way in and got no change.  I pulled it and gave it the old
evil-eye (no obstruction seen), put it back, and no change.  Ron Munson
at Performance said that they had no problems on testing so it leaves me
scratching my head.  Today we'll pull the aux oil pump out of the
system, cap the ends, and see what happens.
  
 
Robert, while at General Motors I worked on an aluminum body positive
displacement oil pump identical in operation to the Continental TSIO 550
oil pump. Here is what I know.  The aluminum body makes the oil pump
performance with warm to hot oil very sensitive to gear clearances. The
gear body cover needs to be very flat, the gear bores must be very close
in clearance to the gears, etc. When the oil is cold, the aluminum body
is cold and the clearances are close and the oil pressure is good.  As
the oil heats up the clearances increase because the aluminum body
expands faster than the steel gears.  The worst case oil pressure will
always be at idle with hot oil.  With that said, IF the oil pressure was
good at idle and at hot (normal temp at landing) oil temp at one time,
then something has changed and the first thing I would check is the
pickup tube for cracks and for other leaks (gaskets or pressure
regulator).  The oil pump did not wear out in just a few hours. If you
can not find any leaks, I would replace the oil pump with a new one.
Rebuilding your current pump will not likely have the results you are
looking for.
Craig Berland