Loss of Oil pressure

[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.

[T. C. Downey]

worn main bearings usually show low oil pressure at idle, but normal at cruise RPM.

I don't believe that is the case here.

[T. C. Downey]

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

Re-thinking this, that filter by-pass can be wide open, it would not dump off pressure, it will simply by-pass the filter, the oil will still go to the engine and depend upon the bearing clearances to achieve the restriction to cause pressure. But the adaptor may have developed leak at the "o" ring seals where it fits into the accessory case, this could happen in flight.

one of two things are happening here, the pump is not getting oil from the sump, or it is being dumped off due to a open in the system. the later is my suspicion.

seeing as the first indication was in flight, and there are few moving parts in this system, I would believe the pressure relief valve or a "O" ring seal is the culprit.

[Bruce Fenstermacher]

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.

I did not mean to imply I suspect worn bearings in this case. The test I described would eliminate that and show the problem to either be in the accessory case or the rest of the engine.

FYI wearing bearings would likely show in a oil analysis if they were done often enough and enough valid data was available to show a change. I totally wiped out a new set of main bearings in by Cub in less than 45 hours. In that time I changed the oil and cleaned the screens many times as I chased my increasingly lower oil pressure problem. I never saw abnormal metal in the screens.

[c170b53]

Looking at the pics.it looks like some kind of sealant was used with the fabricated gasket. Did the sealant not adhere in the area which is "black" and if so where is that sealant now? The oil pump is very straight forward, remove the four bolts, the plate and you'll have two gears in a recess. The bores of the oil pump chamber do wear when the gears eventually wobble in the case but like the bearings its a gradual process which takes time to manifest itself in a low PX indication. Looking at your engine cases from the rear you can see the two ports: L/H the pressure supply and R/H pressure return galleries just above bottom of the engine cases above the sump studs.

[johneeb]

Gmanic acc.jpg

Have you looked at the pan gasket in the area of the arrow (where pressurized oil flows from the pump through the oil pan gallery to the left case half main oil gallery), you mentioned you did earlier remove the oil pan and reseal it.

[Gmanic]

Well, what can I say - I think we got it.
Last post seems to have nailed it.
We did remove the pan and the gasket right around the described area was torn, opening up a channel into the oil pan.

Thanks a million.

After cleaning the pan we also noticed a crack around the forward drain plug, I called Drake Air in Oklahoma who have done good work for me before and
they can weld it for $550 plus shipping.
I asked them if they can weld shut the forward drain plug which has no purpose anyway and they said they are looking into it.
Before I send it off (20-25 business days turnaround) - does anyone know of a replacement pan for less $$$?

I'll post that question as a new thread.

[blueldr]

What do you expect to get for a $550.00 welding job? I would sure as hell expect more than the welding for that price.
Do they offer any sort of a guarantee or some sort of exotic paperwork covering the job?
Some many years ago I was building a 1/2 Volkswagen engine and had the magnesium cases welded up for a whole lot less than that.

[Gmanic]

Well, that actually turned out nicely.
The new problem is unrelated.