propeller feathering while ground run

[TomM]

Bill:

I normally have great oil pressure (50 or better in cruise) but last fall I was flying and the front engine was down to the bottom of the green arc. When I landed and powered back, the pressure went to just above zero. The easiest thing to do if you are contemplating low oil pressure is to make sure the relief valve is not scored and the spring is good. On a "new" engine with junk in the oil, I would check the relief valve port for contamination.

My oil pressure issue was caused by a tiny piece of something (non-magnetic) stuck on the seat of the plunger. If the plunger is displaced at all with hot oil, the pressure will be too low.

See the attached picture of my contamination. Once cleaned and put back together - 50 psi hot all day long again.

[mshac]

Originally Posted by TomM

My oil pressure issue was caused by a tiny piece of something (non-magnetic) stuck on the seat of the plunger.

If that pic is the head of a Q-tip, that piece of debris was tiny! Its amazing the large impact such a tiny piece of junk can have.

[cessnadriver]

TO: mshac and TomM.
Thanks guys for your replies/suggestions.
I replaced the oil relief valve plunger with one that was in better condition. Added three washers, but didn't seem to make a difference.
Oil pressure at start up is 40 PSI, and goes to 32-35 PSI after warm-up(10 minutes). At that time the prop slowly goes to feather. Yes I can lock the prop with a paddle back to low pitch. I can hear the latches lock on. Checked the cylinder pressures, cold, all but number 3 and 4 are 78/80 the others 60-62? Did the fuel in oil and check the pressure at the prop governor pad, suppose to be 20-50 PSI, mine is at 20 PSI. The engine only ran for 0.5 hour after overhaul so I'd say NO to break-in.
Thanks again for your questions and suggestions.
Regards, BILLS

[mshac]

BILLS:

When was the motor overhauled? Have you spoken with the mechanic or shop who performed the OH?

Are the cylinders nickel, chrome, or steel? What type of rings were installed?

What did you find when you drained the oil? Did you refill with mineral oil?

I've never seen an overhauled engine turn the oil black in .5 hrs.

And those compressions should all be in the 70's if everything is fresh.

[cessnadriver]

MSHAC.
No I didn't talk with the mechanic that overhauled the engine, due to argument between him and the owner of the airplane that I got the engine from. Don't know the kind of cylinders or rings. Oil had small bits of rtv and fine grit in the oil filter, and I'm using multi-grade oil. After counseling with other A&Ps I've decided to remove the engine and send it to a reputable engine shop and have it disassembled, inspected, and reassembled. Repairing anything that needs repaired. In the mean time I'm re-installing my old engine. It was running fine before removal, just leaked quite a bit of oil, mostly from the push rod tube, I think?
Thanks for your questions.
Regards, BILLS

[mshac]

BILLS, I support your decision 110%! The expense is unfortunate, but now at least you should know exactly what you have.

Please let us know what is found.

And I think the rear engine leaks oil on half the 337's out there...the repair is to replace the leaking pushrod tube gaskets, which are held in place only by spring pressure from the pushrod tube against the case. Not a hard job, but you do have to remove the valve cover, rocker arm, and push rod. If you do more than one, make CERTAIN everything goes back exactly where it was!

[Skymasterdriver]

I have seen them go to feather because they get to hot, running a fuel calibration if ran several times it may have gotten hot and lost oil pressure do to get oil so hot it lost its velocity