Oil pressure relief valve

[jrs14855]

The Lycoming's do not like low oil pressure. Any thing below 55# will trash your engine, sooner rather than later.

[Clint B]

My original post was a bit misleading; my experience with the champ was that the oil pressure was fine at lower temps and rpms like when you are warming up and taking off. Lower rpm's seemed to make the pressure come up slightly, like into the 50's. That is what originally made me think I had a bad gauge. Oil pressure seemed to respond to rpm backwards. Cruise rpm made it come down. Perhaps this isn't your problem, but it sure sounds like what I had.

[131RB]

Any chance you could describe or show a picture of your relief valve. Clint is correct and I have seen this issue before. Some engine cases used to have cages that kept the ball and spring in alignment with the seat. Later engines and or modification removes the cage so you now usually only have a seat. In order for the spring and ball to stay in alignment you have to have the correct housing. If not the ball will roll of the seat during higher power settings or times of high oil pressure i.e. Climb and cruise, settling back on the seat at idle. Another indicator will be the oil pressure bouncing a bit in cruise as that needle is trying to seat.
Ryan

[bret]

Not too familiar with this engine....yet, but, if the oil pick up had a leak above the oil bath level, it would suck air at high rpm and cause a lower oil pressure, when rpm came down it would decrease the vacuum on the pickup and allow liquid into the pump and higher oil pressure?

[IowaRV9Dreamer]

Originally Posted by Clint B

There are 2 types of setups on the case where the oil pressure relief mechanism is installed. We will call them the old style and the new style.

Can anyone describe the difference between these, and how to tell which a case has?

[Flyingleap]

I have a O360-A4M. About two years ago an engine start showed zero oil pressure, shut it down. IA brought out his mechanical gage, attached to front of engine, yep zero. As I started to remove the adjust type pressure relief port, heard a "click". I believe that ball was sitting out of its seat. Checked the spring(worn from sliding) ball fine, but looked at where the ball seats and saw little dimples around this area (oh, and no cage). Put it back together, engine start, 50 lbs or higher at idle, fixed. IA scratched his head.

Now, this last year I overhauled the engine and sent the case to DIvco for overhaul. I talked with the guy that actually inspects that area of the case.
He said that dimpling has been seen before and he would machine that area.
BTW, there are seven inspectors for the case, setup in stations and each machine a certain part of that case.

I think there should be a a cage for the spring and ball. There are five different colored springs for the many lycoming variants but nothing to hold that ball spring aligned with the seat. Just a small particle of carbon can generate almost no oil pressure, BTW. John

[celstar]

Replaced the oil pressure relief valve and problem solved.