Oil pressure problems... Ideas?

[ADK_Cub]

Hello all![emoji1366]

I normally just read and observe, but I am truly stumped with this problem and am in need of some help big time. Ok right too it.

Engine is 0-320, fresh back from major overhaul with less than 5 hrs on the break in, from a very reputable engine builder. Remote oil filter previously installed.

Start the engine makes great pressure, run up, take off and rip around the patch 5 times or 10 minutes everything is fine (2400rpm). Shortly after that the problems arise. Pressure starts to slowly decrease, panel mounted gauge and “tee-d” in gauge to the right front oil galley. Panel gauge spikes 10psi intermittently as it drops over the course of 10 minutes before it gets to 45-47psi and we chicken out and land. Suspect that the cheap tractor gauge, and long input tube for the tee in gauge hampers the detection of oil pressure spikes. Have not tested oil temp bulb for accuracy yet. Oil s

On final and in reduction of power 1100-1500rpm pressure comes right back up to green arc and stabilizes. Wtf

Sump screen clean and inspected, pressure relief valve, has new spring and is shimmed properly, no change. Oil temp by pass was both left in and removed for different test flights, no change. All oil lines clean and unimpeded. New oil filter, and purged input line to panel gauge, no change.

Can’t figure this one out for the life of me.

Stable first lap or two



Pressure drops



On final



Hopefully those post correctly. Any help would be greatly appreciated. Cheers [emoji482]


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[DENNY]

How was the crankshaft inspected at overhaul? Any work done to crankshaft? You only have viscosity valve and no vernatherm correct?
DENNY

 

[Steve Pierce]

What does the engine shop say? I take it the crankcase was overhauled and has the updated oil pressure relief valve seat and the updated oil pressure relief valve housing?

 

[mike mcs repair]

oil hose with "flapper" in it (chuck of rubber in hose that's not installed properly in hose end(cut)).... most likely going to remote mount filter....

 

[ADK_Cub]

How was the crankshaft inspected at overhaul? Any work done to crankshaft? You only have viscosity valve and no vernatherm correct?
DENNY

Crank was magnafluxed and measured at inspection. The engine shop informed me that it only had “one more re size before it’s needs to be replaced” and correct no vernatherm.

Found a couple “flappers” one with as much as 60% obstruction. Re placed hose ends and surprisingly, no change.



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[ADK_Cub]

What does the engine shop say? I take it the crankcase was overhauled and has the updated oil pressure relief valve seat and the updated oil pressure relief valve housing?

Shop says bring the engine back. Unfortunately this is the second time removing from the plane and bring it back, first time was bc the engine wouldn’t make full static RPM and it turned out to be a “camshaft timing gear with a mis scribed timing mark.” Luckily it was only about one tooth off causing improper valve overlap and nothing worse. But that was 2 months of diagnosis and head scratching by my mechanic before it went back the first time.

And correct, updated oil pressure relief valve and housing. The spring had broken some time very shortly after overhaul. Once discovered we thought oh man this has got to be it. Engine shop explained it was a “bad batch of springs”, sent replacement and believe it or not... no change.

It’s actually kind of amazing how many little things can be wrong with these engines and they still run, kinda. [emoji23]


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[Oliver]

I’m not clear on your pressure gauge set up.
you are taking pressure off front of engine with both gauges?
theyre both consistent when pressure drops?
Have you tried taking pressure from port next to pressure relief valve?
A “flapper” would affect flow volume, unlikely to affect indicated pressure,
Maybe get a good (known to be accurate) gauge and run it direct to gallery by relief valve, keep it simple as possible, minimal fittings no “Ts” and see what happens. At least eliminate the most likely culprit.
45 psi is not normal but it won’t grenade engine during trouble shooting.

 

[Gordon Misch]

It's late and I probably shouldn't be shooting my mouth off, but - - - sounds like you've already had a couple of issues with the very reputable engine shop, that also sound like they could possibly be questionable excuses. Gear timing marks stamped wrong? Yeah, right.

Oil pump clearances out of tolerance and cavitating?

 

[ADK_Cub]

I’m not clear on your pressure gauge set up.
you are taking pressure off front of engine with both gauges?
theyre both consistent when pressure drops?
Have you tried taking pressure from port next to pressure relief valve?
A “flapper” would affect flow volume, unlikely to affect indicated pressure,
Maybe get a good (known to be accurate) gauge and run it direct to gallery by relief valve, keep it simple as possible, minimal fittings no “Ts” and see what happens. At least eliminate the most likely culprit.
45 psi is not normal but it won’t grenade engine during trouble shooting.

The panel oil pressure gauge is measuring from normal outlet on the back of the motor and the temporary gauge in these photos is measuring from the right front oil galley (we just removed plug and threaded in fitting and line). At one point we had just tee’d in the temporary gauge to the panel gauge input line to verify if the panel gauge was measuring properly. And it was.

Both gauges start dropping pressure at the same time, obviously the temporary gauge is about 10psi lower then the panel gauge. Which I think should be normal given there is less pressure at the right galley compared to right above the pump where the panel gauge is measuring from.




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[ADK_Cub]

It's late and I probably shouldn't be shooting my mouth off, but - - - sounds like you've already had a couple of issues with the very reputable engine shop, that also sound like they could possibly be questionable excuses. Gear timing marks stamped wrong? Yeah, right.

Oil pump clearances out of tolerance and cavitating?

I trust the shop and the engine builder. He had my old cam gear and the overhauled gear and showed me the marks being off. Just bad luck.

I’ve never built a airplane engine but on gear driven oil pumps on Harley’s we match and shim oil pump gears to housings for specific tolerances. I have new oil pump gears in this motor. Is it possible that “new” gears paired “old” gear housing/case could be too far out of tolerance to maintain pressure? I would think it wouldn’t build pressure at all. I couldn’t find any mention of tolerances or clearance in the lycoming overhaul manual.


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[skywagon8a]

Crank was magnafluxed and measured at inspection. The engine shop informed me that it only had “one more re size before it’s needs to be replaced” ....

I trust the shop and the engine builder. He had my old cam gear and the overhauled gear and showed me the marks being off. Just bad luck.

I’ve never built a airplane engine but on gear driven oil pumps on Harley’s we match and shim oil pump gears to housings for specific tolerances. I have new oil pump gears in this motor. Is it possible that “new” gears paired “old” gear housing/case could be too far out of tolerance to maintain pressure? I would think it wouldn’t build pressure at all. I couldn’t find any mention of tolerances or clearance in the lycoming overhaul manual.

This is indeed a head scratcher. Prior to reading post #10 I was thinking "oil pump"?. When first started oil is cold/thick pushes pressure higher. When oil warms/thins there is not enough pump capacity to push enough oil through the system to make the higher pressure. When the power is pulled back there is not as much demand/internal leakage thereby the pressure can build back to normal.
Two things, you have new oil pump gears. And, the crankshaft only has one grind left on it's life before becoming too undersized for use. Crankshafts don't usually wear down unless they have LOTS of hours on them or have been badly abused.
Conclusion IF the steel crankshaft has this many hours on it, how many hours are on the aluminum accessory case? How much wear is on the aluminum accessory case next to the steel oil pump gear? IF there is a lot of wear here then when cold the oil will build pressure. When the oil is hot it can bypass/leak between the gear and case thus not pumping into the engine. It is normal to find circular scratch marks on the accessory case next to the steel oil pump gear as well as the oil pump cover plate. If this accessory case has as many hours as the crankshaft, it may be worn out enough so the oil pump just can't do it's job.

This is just speculation on my part. Certainly is a place to look.

 

[n40ff]

What Skywagon says above makes sense except for,

"On final and in reduction of power 1100-1500rpm pressure comes right back up to green arc and stabilizes. Wtf"

That to me is a head scratcher.

Jack

 

[Steve Pierce]

The oil pump should cavity should have been measured at OH and then checked with the new pump installed to see what the clearances are. I'd remove the engine and return it to the shop. Doesn't take long to R&R. Is the engine shop running it on a test cell?

 

[skywagon8a]

What Skywagon says above makes sense except for,

"On final and in reduction of power 1100-1500rpm pressure comes right back up to green arc and stabilizes. Wtf"

That to me is a head scratcher.

Jack

Let me try to explain the thought in different words.
An engine uses the flow of oil for it's functions. It requires a certain volume for this purpose. When the engine is operating at it's highest power/rpm setting it is consuming it's maximum volume of oil. SO, The oil pump must have the capability to provide an amount of oil which will provide an excess amount of oil which would account for the normal and excess wear in the engine. This is where the relief valve comes into play to control the maximum pressure. The worn pump is struggling to provide enough volume to unseat the relief valve.

Now to your Wtf? When the power is pulled way back the oil requirement is not as high. The demand and rotation speed of the pump is lower. Since the pump is running slower, the cavitation which is caused by it's excess clearances and the higher rotation speed of the gears is reduced. When the cavitation is reduced the pump can direct it's output downstream, thereby being able to provide higher pressure to the engine.

Does this help?

 

[mike mcs repair]

when this is happening, can you shut down and quickly check dip stick? is oil all "bubbly"

I had one where I left a pipe plug out of oil galley internally, and it was dumping oil back into pan.... the engine shop guy clued me into that check... he even knew which plug I probably left out....

do you have something internally dumping oil?

this kinda ties into your, reduce power/rpm and oil pressure goes up some??? or not???

i assume you have checked filter for metal?

 

[Gordon Misch]

I couldn’t find any mention of tolerances or clearance in the lycoming overhaul manual.

This is a small part of a spreadsheet I put together with all of the sizes to check. It's from the Lycoming O-320 Table of Limits. The columns from left to right are: Table of limits Reference Number, the measurement on my engine, Minimum size, Maximum size. The min and max are new limits, not service limits.

Edit: I'd be happy to share the entire spreadsheet if anybody would like. It's in Google Sheets. There is an additional column which compares the measured values to the specs with a quick "ok" or not. Avoids having spinning eyeballs from looking at the numbers! It only has new limits. I didn't refer to service limits.

[TABLE="width: 0"]
[TR]
[TD="align: center"]Oil Pump[/TD]
[TD]Impeller diametral clearance[/TD]
[TD="align: center"]542[/TD]
[TD="align: center"]0.0025[/TD]
[TD="align: center"]0.0020[/TD]
[TD="align: center"]0.0060[/TD]
[/TR]
[TR]
[TD][/TD]
[TD]Impeller side clearance[/TD]
[TD="align: center"]543[/TD]
[TD="align: center"]0.0025[/TD]
[TD="align: center"]0.0020[/TD]
[TD="align: center"]0.0045[/TD]
[/TR]
[TR]
[TD][/TD]
[TD]Drive Impeller width[/TD]
[TD="align: center"]543[/TD]
[TD="align: center"]0.7477[/TD]
[TD="align: center"]0.7470[/TD]
[TD="align: center"]0.7490[/TD]
[/TR]
[TR]
[TD][/TD]
[TD]Driven Impeller width[/TD]
[TD="align: center"]543[/TD]
[TD="align: center"]0.7487[/TD]
[TD="align: center"]0.7470[/TD]
[TD="align: center"]0.7490[/TD]
[/TR]
[TR]
[TD][/TD]
[TD]Driven Impeller/Idler shaft clearance in housing[/TD]
[TD="align: center"]544[/TD]
[TD="align: center"]0.0021[/TD]
[TD="align: center"]0.0010[/TD]
[TD="align: center"]0.0025[/TD]
[/TR]
[TR]
[TD][/TD]
[TD]Drive shaft / body clearance Big end[/TD]
[TD="align: center"]545[/TD]
[TD="align: center"]0.0018[/TD]
[TD="align: center"]0.0010[/TD]
[TD="align: center"]0.0025[/TD]
[/TR]
[/TABLE]

 

[flynlow]

When rpms are reduced and pressure increases makes me think the oil is foaming
Any chance wrong oil ?
Pretty simple to drain and refill


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[N86250]

These are the timing gears of an A65 Continental after the timing was corrected. In the yellow circle the single dimple on the cam gear was almost invisible until touched with a white marker. The arrow points to a line that looked to be machined into the cam gear. Somebody used that line for the timing mark. The engine behaved unexplainably crazy and it took awhile to find why. The guy who did this had overhauled several engines satisfactorily and this was his first small Continental.

 

[ADK_Cub]

Skywagon your theory makes perfect sense. Like a prop blown out at hole shot just to have it bight again if you back off a touch. The crank was ground because of corrosion this last go around. It’s a older narrow deck o-320 so I’m sure it no spring chicken but a lake overturn destroyed old logs so who knows on the history. This engine wasn’t due for overhaul, just given its history I wanted a fresh slate when I purchased the plane. Combo of submersion and mothball time convinced me to tear it down. It had run strongly after submersion and plane being rebuilt for 15ish hours, but then sat for 6 years and wasn’t greatly documented.

Oil is 100 mineral oil for break in.

The internal oil plug theory is a good/plausible one. I’m unaware of the inner workings of the galleys and what requires plugs and what doesn’t. Or what could have been forgotten.

Excessive oil aeration causing inconsistent flow to the screen and sump pick up is certainly another. I added another quart when I suspected this to bring it up to 7.5 in hopes of keeping it submerged. Didn’t see a ton of bubbly oil, but that’s not saying much.

Gordon thank you for the specs on that, I’ll copy and save.

The engine is off the plane now and headed back to the shop. Phone calls and emails between engine builder, my mechanic, and myself and have exhausted almost all external possibilities. Except oil pump housing and gear tolerance. That has not been checked.

Engine builder does have a dyno that he runs the engines on before they get shipped. Which led us to believe that this was an AIRPLANE problem, and not an ENGINE problem. Basically just meaning external oil system parts that don’t go with the engine to the builder.


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[ADK_Cub]

I’m really really hoping that the tell tale of the oil pressure jumping back up when the power is reduced rules out the crank and bearing tolerances being to fat.


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[n40ff]

Skywagon

Understood. Thanks.

Jack

 

[Oliver]

ADK,
Please let us know what you find out. A lot of these issues pop up and then are quietly resolved over time.
It would be interesting and educational to find out what caused this issue.
Sounds like you are on the right path, best of luck and thanks for posting.
Doug

 

[PerryB]

How about the suction tube leaking where it bolts up to the back of the pump?

 

[ADK_Cub]

How about the suction tube leaking where it bolts up to the back of the pump?

I thought the feed line to the pump was integral to the case from the sump screen. Maybe I’m not tracing it out right.


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[jliltd]

One more thing, be sure and check all of your oil hoses very carefully. Aside from the pre-mentioned flapper caused by a loose enf fitting mandrel tool, you need to make sure that the hoses are fairly new. You see, many times on older hoes can have an internal delamination of the rubber from the reinforcing, happens with 303 and others. This can create a baloon somewhere along the length of the hose. On a suction side that baloon can expand and constrict fluid flow at higher power settings. Then when you pull the power back and the flow decreases that balloon goes back in a normal shape allowing full flow.

So if I were you I would rebuild my oil hoses (or replace with new). That's a lot cheaper test than teardowns etc. And who doesn't like a new hose. You could also take the opportunity to upgrade to lifetime teflon type hose for $$ more.

Jim

 

[ADK_Cub]

Dang Jim that’s a good point, thanks. The hoses would probably appear to be fine visually but I’m sure if I pinch them I could feel a soft spot.


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[stewartb]

I’d be inspecting push rods and rocker arms and valve springs. Because I had a very similar experience after building a hot rodded car engine.

No perceptible change in how the engine is running when the pressure drops?

 

[skywagon8a]

One more thing, be sure and check all of your oil hoses very carefully. Aside from the pre-mentioned flapper caused by a loose enf fitting mandrel tool, you need to make sure that the hoses are fairly new. You see, many times on older hoes can have an internal delamination of the rubber from the reinforcing, happens with 303 and others. This can create a baloon somewhere along the length of the hose. On a suction side that baloon can expand and constrict fluid flow at higher power settings. Then when you pull the power back and the flow decreases that balloon goes back in a normal shape allowing full flow.

So if I were you I would rebuild my oil hoses (or replace with new). That's a lot cheaper test than teardowns etc. And who doesn't like a new hose. You could also take the opportunity to upgrade to lifetime teflon type hose for $$ more.

Jim

Jim, reread the following. He used two separate oil pressure gauges sources from two different locations with the same result. Nothing wrong with new hoses but this issue isn't the hoses.

The panel oil pressure gauge is measuring from normal outlet on the back of the motor and the temporary gauge in these photos is measuring from the right front oil galley (we just removed plug and threaded in fitting and line). At one point we had just tee’d in the temporary gauge to the panel gauge input line to verify if the panel gauge was measuring properly. And it was.

Both gauges start dropping pressure at the same time, obviously the temporary gauge is about 10psi lower then the panel gauge. Which I think should be normal given there is less pressure at the right galley compared to right above the pump where the panel gauge is measuring from.

 

[Pacerfgoe]

Have you changed the oil filter? Maybe something internally going on there.

 

[jliltd]

I didn't say the hose going to the oil pressure gauge. I said the oil hoses. There are a few around the engine. Remember these things are all hooked up in series, not parallel. More specifically the most common culprit is the oil cooler hoses. I got this from the late great Monte Barret himself. I had the same issue on a 4-cylinder Lycoming. And Monte nailed it.

Jim