Thorp Air Command - T18.net

Looking for input on low pressure.

I have an O-290-G overhauled by an A&P in Houston. The engine has 200 hrs on it and runs good with no temp problems. The oil pressure is a constant 40 psi. The previous owner also experienced oil pressures of 40psi.

After reading the GPU conversion manual stating the pressure should be 60 I started looking at ways to improve oil pressure. This is what I have done so far.

1. Tried different viscosity oils.

2. Removed oil pressure control spring and ball, changed spring and ball and stacked washers.

3. Seated ball using lapping compound.

4. Checked pressure from different places on case.

Any ideas before I remove the accessory case and check the oil pump gears?

Has the guage been checked?, and, out of everthing you have done has there been any difference at all or does it always run a constant 40 Psi even when it is warm.....Dan

I am with Dan . Start with the easy stuff before tearing the enging apart . First of all is the gauge...

1. Direct read or does it have a "sender ."

2. You say the pressure is constant at 40 psi ? Does RPM affect that reading ? Low RPM , low pressure . High RPM , high pressure ?

3. You took readings from different places using what type of instrument/gauge and they all read 40 psi ?

RB

Checked gauge against new auto supply unit and reads correct, replaced w/ new tubing.

Got 40 psi cold from accessory case right and left. Tried the temp. port on the screen housing too all 40psi.

Warm engine will have lower idle pressure otherwise steady 40 at all RPMs.

Thanks for the input Chuck

I had an 0-290 and I was flying along and saw my oil pressure creep all the way down into the 40s but my oil temp and other reading stayed the same. I landed and added a quart (or two I cant recall now) and the pressure came back up to normal.

Steve Hawley did you read this thread? Take a look at what's going on here and see what you think. Maybe something in the bypass? Not enough washers could it be bypassing too much? If the bypass hasn't enough on the spring it would hold a steady 40Psi would it not? What do you think Steve? Dan

Did you replace the pressure spring with another gpu spring or with one from a certified (non gpu) 290 engine?

Bernie

Spring and ball came out of 0-290-g that ran at 80 psi hot. I don't think the ball is being unseated by oil pressure as more washers make no difference to pressure.

Local A&P thinks the case may be worn around gears allowing oil to get past.

The pressure regulating spring only regulates the pressure that is allowed by the "passage" of oil through the bearings and other wear surfaces. You have done all the things I would have done and the most likely solution is to pull the accessory case and look at the scroll surfaces of the pump and the condition of the gears. On a small bore Continental engine 40psi would be high. I've often wondered what would happen over the long term if you just continued to run the engine at 40psi. I'm not suggesting you do this, just curious.
Steve Hawley

Steve: I was thinking the same thing. As a GPU this engine runs at 25 psi oil p. I think the higher pressure is for cooling, extra oil sprayed on pistons. My Engine runs cool so no galling of internals is indicated.

Lycoming wants at least 50 psi. for sprayer in crankcase to function but this is for more modern 0-320/0-360. I don't know if the G has a sprayer. Photos and drawings I found are not clear. Anyone out there been inside a 0-290-G ? Have you seen a sprayer?

Thanks for input Chuck

If you have the "paper work/logs" maybe the A & P in Houston can shed some lite on the innards and explain the 40 psi ? I would assume he did a bench test and has all the numbers , compression , max RPM , min/max oil pressure , etc .

RB