Loss of Oil pressure

[Gmanic]

Bad News,
the engine is assembled again and hung back on the airplane.
With plugs out it was motored with the starter and again failed to show any oil pressure.
Is it possible that pressure is directed towards the oil pan from the inside?
The foreward drain plug still shows a leak despite a new crush washer and sealant.
Maybe we still have an internal oil leak?
Someone mentioned something about a freezeplug- do we even have those?

[FredMa]

The left oil screen on the acessory case it the low pressure or scavenge screen. This is what takes oil from the sump and supplies it to the pump inlet. From your description it seems as though you have determined that not to be the problem. The pump is a positive displacment pump, meaning it produces a specific displacment for every revolution. At low speeds though it is very ineffecient, not sure if using the starter in an attempt to produce pressure would work even if everything was working normally. When operating normally pressure is produced due to the pumps positive displacment being greater than the rate of oil flowing through the engines components, If your pressure relief valve were stuck open, for example. oil would simply flow through and back to the sump with no restriction and no pressure would be produced. It is possible, I guess for the internal passages to have a hole or crack allowing oil to escape and flow back into the sump, but I have never heard of such a thing happening and think it is extremely unlikely to be the case. There have been cases of the crankshaft bearing support cracking, it has an internal passage that supplies the crank bearings with oil from the oil gallery on the left side of the engine case. Unfortunately this may be something you may want to check (requires removal of cylinder) Do a search on here for that problem. The left side oil gallery also supplies the cam and cam followers and then sends oil out through the push rods to the rocker arms. I've never heard of anything cam related causing this type of problem though.

[c170b53]

Tell us what was found with the sump, what degree of corrosion was found and did you dye check for cracks around the drain plug boss?
Did you remove the oil px nipple (with the restriction), replace it with a AN adaptor (nipple) without a restriction, make up a small line and hook up a remote gauge and see what that reads.
The oil galleries run in each case half, back to the front and at the front of the cases at about the 9 and 3 o'clock
Position you'll see a plug with a recessed hex head. Removing those plugs gets you a look at the oil galley insides. The left hand galley supplies the px the right the return? I'll post a schematic of the oil system maybe that will help you visualize the oil flow.
Please let us know what you have done specifically, otherwise it will just be a guess fest. As an example you may have just checked with lock wire to see if the restrictor was plugged which isn't a bad idea unless the object that maybe blocking the oil flow just gets pushed into the engine and then px pushes it right back next time you crank. I'm not saying that's what is occurring but rather how the idea, the intent and the execution can go awry.

[c170b53]

here's the flow

o-300c-0il-flow.jpg

[GAHorn]

Some times, during re-assembly of the oil pump and accy cover, the oil pump gears "lose their prime" and have a difficult time recovering. In other words...the gears turn...but they only move air, unable to suck up oil and pressurize it.

The reassembly of an oil pump is best done by filling with heavy oil or light grease (such as "lubriplate" aka "duck butter"). This will allow the pump to start rotation with filled air-spaces and thereby immediately able to suck up oil and send it on it's way.

If your pump has lost it's prime, you might consider pressurizing it with a grease-gun filled with engine oil and pressurize the system thru the gallery (or oil pressure nipple, etc.) back'filling the pump. (This can be assisted also by turning the prop backwards while pressuring from a downstream position in order to full the oil pump chambers.) This can also be done by pressurizing the pump thru a suction-screen fitted with a nipple in lieu of a oil-temp fitting (as some of them are.)

Of course priming the pump is best done at original install of the pump w/lubriplate.

[T. C. Downey]

I would suggest removing the oil filter adaptor and replace it with the OEM screen, fill with oil, run the engine and see if the il pressure comes back, indicating the oil filter adaptor is faulty.

[Gmanic]

We motored the engine today - spark plugs out and fuel and ignition off.
After 30 seconds we did get some oil out of the nipple where the pressure gauge connects.
One or two drops, not pressurized oil.
Thanks for all the suggestions, please remember that the initial oil pressure loss occurred during flight.
Does anyone know of a good engine expert in the southern New Mexico/West Texas area?
If I have to send the engine in - any suggestions for an engine shop?

My friend and mechanics are thinking to pull the motor again and dye-check the oil pan.
The forward drain plug is still leaking despite new crush washer and silicone sealant.
Thinking the might be a crack somewhere.
He thinks it is an internal leak pushing oil into the oil pan, just don't know where it is coming from.
The bend up gasket is the only piece of evidence we have seen.

Thanks again.

[Gmanic]

I just joined the association so that I can upload pictures.
Waiting for the feature to be turned on.

[c170b53]

Welcome, thanks for joining, I hope we can help you and as well I think you may find other benefits of being a member. In my previous post I mentioned the plugs behind the prop flange in the case as being in the 9 and 3 o'clock position, really they are more like the 8 and 4 o'clock position
Utilize the search function in the forums, you'll find a bit of info on the sump. I don't know how well it was cleaned but the internal surfaces may appear to be normal until you use a solvent and mechanical pressure to clean the surfaces. Corroded magnesium at the bottom of the sump will have a consistency of wet sand and may remain in place until mechanically displaced.
I think there's good advice given by others in this thread worth exploring before shipping off the motor.

[T. C. Downey]

My friend and mechanics are thinking to pull the motor again and dye-check the oil pan.
The forward drain plug is still leaking despite new crush washer and silicone sealant.
Thinking the might be a crack somewhere.
He thinks it is an internal leak pushing oil into the oil pan, just don't know where it is coming from.
The bend up gasket is the only piece of evidence we have seen.

Thanks again.

I would not pull the engine just yet, reading this last post, I understand that you have flow, but no pressure.

Pressure is.. a resistance to flow, So if the by-pass in the oil filter adaptor is open, you will have no resistance.

Pull it off and put the old screen back in, see what happens.

also pull the pressure regulator under the big brass nut on the right rear of the case. If it is held open by FOD there is no way the pump can create enough flow to get pressure.

Are you indicating RPM while cranking? Tach drive is the oil pump gears. no tach indication no gear rotation.

OBTW, did your new oil sump gasket have the proper holes in it, and were they placed in the proper position ? they can provide a gap in the pump suction side, when the sump gasket is flipped the pump can't prime, because the pump is sucking air from the crankcase, rather than oil from the sump. To trouble shoot this, add oil to over flow the sump and cover the gap between the sump and case. If it primes the pump and provides a pressure indication, you sump gasket is installed wrong.

I'd pull the filter adaptor first.

[Gmanic]

Thanks for the fast response - time IS critical.
Here two pictures, the first the displaced gasket, the other the back of the engine, it appears that oil can flow UP into the hollow chamber on top of the two openings for the oil screens.
Note how the center portion is dark in color and bent up towards the oil pump.

[Gmanic]

We will follow the recommendations and I will report back.

[Bruce Fenstermacher]

Look at your own pictures. The part to the gasket that is dark and may have not been sealing has nothing to do with the flow of oil. All that would happen if this area was open is that area in the accessory case would fill with oil and never drain out.

The path oil follows is to be sucked up through the lower pressure screen into the pump through galleys internal to the accessory case. Then through the pump and back down another internal galley. Through the high pressure screen and back up an internal galley to one of those small holes you see on the side middle edge of the accessory case. Only two holes between the case and the sump and the case and the engine half are pressurized and would have to be sealed to effect oil pressure.

Oil path in accessory case.png

The oil then runs down the galley in the case halves and sent to the crank bearings, cam and hydraulic lifters. This is why worn crank bearings greatly effect oil pressure. They are one of the first wear spots for oil to leak out of the pressurized side. if oil makes it to the other case half it travels down the galley to the pressure relief valve.

As Tom and others have stated, if the pressure relief valve is held open, you will not have any oil pressure. it will just bypass back to the sump. BTW, the pressure relief valve is a high pressure relief not a pressure adjustment. Under normal conditions the valve is never open. The pressure relief valve is NOT like those found in Lycoming engines which is a bypass setting the idle engine oil pressure.

If I were you since the engine is out and this would be somewhat easier. I'd fashion a simple pump from an oil can and attach it to one of the from case half galley plug holes. then holding your finger over the left case half galley hole, attempt to pump up oil pressure at the oil pressure nipple. I don't know if this (the oil can pump) is capable of producing enough pressure but I'll bet it is and it might prove the oil galleys are clear and the bearings are tight enough to maintain pressure.

Then as Tom has suggested, I'd look at your oil filter adapter.

[Gmanic]

Thanks for the quick reply, Bruce.
Would worn crank bearings show as metal in the oil/ oil analysis?

What we still wonder about is how the engine could have run normally in flight
for two hours and then lost it's pressure.

[blueldr]

The results of worn bearings are not likely going to be evidenced suddenly in other than a catastrophic failure.