Engine overhaul/new prop low oil pressure

[74657]

As many of you know, 888DF had a gear extension issue in February that took out my prop.  The engine was overhauled after being ferried home for repairs once the new Hartzell prop arrived.  The airplane went up for a test flight and after the oil got above 160F the pressure dropped to 20 psi.  The prop governor was suspect so it was sent to a different shop (was sent off during OH) to be checked out and it was fine.  The engine guy pulled the engine today and took it back to his shop.  He just called and said that everything appears fine.  He is being very accomodating and has put all of his other jobs on hold until mine is back up.  Lets hope they figure it out.....

 

 

[jetdriven]

did he actually split the case and measure then bearing clearances? check the oil pump?

[Shadrach]

Can you be more specific? Were you flying the plane?  Normal pressure to 160df and then a quick drop off, or a gradual drop? Was the plane started again on the ground to verify that the pressure was back to normal with cool oil?

[74657]

The engine has been completely torn down.  The oil pump was brand new.  Bearing clearances check out fine.  The plane was flying when it was noticed.  Repeated tests on the ground show the same thing.  Oil pressure holds steady until the oil heats up then drops to 20 psi when the engine is under load.  I don't know aircraft engines that well but I do know that when this happens in a car engine it typically means that the bearing clearances are too loose.  Not so in this case.  Continental thought that a plug might be missing, none found.  The engine guy still suspects the prop governor because everyone tells him its the wrong one for the engine, which it is but is covered under the STC for the Missile.  It worked just fine before the engine was overhauled.

Could something in the prop be causing this?  That is brand new as well.

 

[N601RX]

If the governor/prop is suspect I would look for a way to temp block off governor or remove it.  This is pretty easy to do on lycoming, not sure about continental. You mentioned a while back that you had to buy a new crank.  Some lycoming cranks have plugs that have to be installed in them.  Not sure about Continental.

[N601RX]

Also is it possible a oil line or cooler is partially blocked?

[Shadrach]

Did you try and cycle the prop during the pressure drop? I too have an aftermarket Prop governor. Mine is a PCU5000 it is smaller lighter and pumps at a higher volume. Mine has been great.  I do not see how that is the variable.

All of the simple stuff like gauges have been checked?

[Shadrach]

Actually as I think about this, check everything down stream of the vernatherm... I am not a continental guy. It seem that your problem is occuring the moment it starts to open...

[Shadrach]

I meant "close" instead of "open" with regards to the vernatherm...

Can we assume that the oil cooler has been OH'd?

Does the pressure fluctuate with RPM?

Has the relief valve been inspected and checked for proper function.

 

[tony]

I only know my Lycoming engine, and I hesitate to add this.  By for whatever its worth, I have included a picture of the oil adapter.  The circled part is the value that bypasses the filter if it gets clogged.  On my engine the bypass value wasn’t seated correctly and I had low oil pressure until we fixed it.  The pressure would follow the throttle.

 

Another thing that can happen is the guy who assembles the engine grabs the wrong gasket for the adapter and a sneak oil path is created between the adapter and the accessory case essentially bypassing the oil cooler.

 

[Shadrach]

I think a possible solution would be to remove the pan and pressurize the system with an external pump...

[Kevin]

Looks like I got here kind of late, but I usually refer my customers to this Lycoming Service Instruction when they have this kind of trouble.

Kevin

[Skywarrior]

Lycoming Service Instruction: SI-1462A Prop Oil Control Leak Test

 

Chuck M.

[Kevin]

Sorry, for some reason I couldn't post the Service Instruction. The Service Instruction number is SI 1462A, and you can get it off the Lycoming Website:

http://www.lycoming.com/support/publications/service-instructions/index.html

[Kevin]

Another thing, if you are reading low oil pressure on your panel, it has NOTHING to do with the prop governor. The prop governor is nothing more than a self-regulating pump. It takes pressurized oil from the oil system in your aircraft (at about 50 PSI or so, depending upon the aircraft) & boosts it up to about 200 PSI or so to run the prop. Your oil pressure gauge isn't "looking" at prop oil pressure. It's looking at engine oil pressure as provided by your oil pump.

[Shadrach]

This is what I'm saying... If the governor was a factor, I think it would be revealing  itself in a number of other ways as well... Something is either out of tolerence somewher - or - something is impeding flow to the pressure sending unit. Whatever it is, it seems it is happening as the vernatherm starts to open...

[74657]

Engine was removed and completely torn down.  Nothing found except a cracked oil cooler.  The engine is being re-assembled and going to be put back on the test stand afterward to see if the problem shows up again. 

[Shadrach]

OK, so a cracked oil cooler and yet no signs of external leakage???

[74657]

Correct.  No external leakage.

[N601RX]

Do you know if the accessory case was sent out for overhaul also?

[74657]

I just confirmed that the crack on the oil cooler was on the mounting flange, not the cooler itself.

The case was sent out and was machined/line bored.  All bearing clearances have been checked and rechecked.  Camshaft has been pressure tested from both ends (dont know what that means exactly).  The OH shop cannot find anything.  It will be on the test stand tomorrow morning.  The oil pump was sent back for inspection and came back with no issues. 

I'll report back tomorrow.

 

 

[Georgethenault@gmail.com]

so how did this turn out? I am chasing down same symptoms

[carusoam]

Welcome aboard, George.

Plane N888DF was recently being sold again.  It came up in another thread around here...

http://www.ebay.com/itm/1992-MOONEY-M20J-300hp-IO-550-MISSILE-CONVERSION-2500TT-400SMOH-Out-Of-Sight-/142305247282?hash=item21220dc032:g:XHUAAOSwSlBYv0MF&vxp=mtr

It seems to have received an IO550 Missile engine as a result.

Best regards,

-a-

See this thread...

 

Edited March 11, 2017 by carusoam

[Georgethenault@gmail.com]

thanks