Started having problems with my left engine feathering the prop on roll out recently, which also kills the engine.

I noticed that the prop starts feathering below 800 RPM. I then noticed that when I slowed the engine to 800 RPM, the oil pressure is dropping to the top of the red. Increase RPM to max and pressure goes back up, but only to top of the yellow. OK, feathering issue resolved, now what's up with the oil pressure?

On startup, run up, and cruise the pressure is in the green, oil temp is green.

I removed the pressure relief spring today, it looks to be in good working order, marks on the ball bearing indicate it is sealing all the way around.

I saw Frank's issue with the cage being broken. I'll look for that tomorrow.

Any other suggestions?

Bryan,

You didn't mention how long it has been since a prop, governor or engine overhaul. Back when I inherited the plane, it was new news to me that props are 5 years or 500 hours whichever comes first as the recommendation from Hartzell. Learned during this process that a fair amount of sludge can accumulate in the hub area - you might mark the prop position and pull it to see if that is a possible problem, dome pressure may also bear checking.

Please post the resolution so we can all learn. Thanks.

Pat, governor and engine have 1100 hours, prop has 650 hours since overhaul in 1995. Pulled prop and took it to the prop shop. Disassembled, everything is great.

I took the prop to the shop BEFORE I noticed the oil pressure problem. If the oil pressure is too low, the prop will feather by itself at low RPM, at that point the engine is not producing enough power to continue to turn the prop, and the engine dies.

So, the prop and governor are ruled out. It is strictly a low oil pressure problem. What is baffling is that the pressures and temps are fine at cruise, it's only after you land that its a problem.

If I had a bearing problem, I think it would be accompanied by high oil temp. I'm going to open the filter tomorrow.

I did have a retired IA tell me that the oil pressure relief spring can lose its ability to push after they heat up, if they are old.

Bryan,

Check the suction screen as well. IMX, the larger flakes of babbitt material show up there. It is not as clear in the filter. I Have seen this once, and the filter wasn't clear, but the suction screen was clear.

I haven't heard about the spring, but if you have then non-adjustable type, you can put some more washers in the bottom of the cap and see if that changes anything.

Bryan,

Tough one. Was the prop self-feathering before it went to the prop shop? Was the low oil pressure happening before the prop shop visit? If these both happened after the prop shop visit, then I'd look closely at the remove, install and any other work done at that time that remotely touches the oil and anything that might have gotten contaminated as a result - Kristin obviously has a good thought above.

Based on my experience, even the best of the best shops can make mistakes. Hartzell, once incorrectly overhauled my right governor three times before they got it right - they adjusted the price accordingly. They did the work, I test flew and landed, squawked and repeated. They were embarrassed but stood behind their work.

I'll be very interested in what solves the problem.

Pat, I now know there was no need to pull the prop. It is operating perfectly. It is feathering due to the very low oil pressure at idle.

Here's what we know as of today. Reinstalled the oil pressure relief valve with 3 washers added. Cut the oil filter and found a few flakes of aluminum, and quite a lot of ferris material. Oil has 30 hours since change. Pulled the bottom oil screen and found nothing. Flushed engine with naphtha and filtered the naphtha as it came out of the oil drain. No FOD found on the rag used to filter the naphtha. Compression checks show all cylinders 70-75 psi cold, so no broken rings etc.

Reassembled everything. On start up, the oil pressure pegged on the high side of the red. Waited for oil temps come up. Pressure stayed up. Ran both engines at 2000 RPM for several minutes, oil temps leveled out in the green exactly the same. Oil pressure in the left engine eventually came down to match the right engine. When both #4 cylinders hit 400 degrees (virtually same time), I pulled the throttles back to idle. Left oil pressure went to low red zone, prop feathered. Increased throttle, oil pressure comes back up, prop comes out of feather.

I'm thinking it is most likely the prop governor or the engine oil pump coming apart?

I believe I've figured out the surging right engine, see update on that in airframe.

Just a thought.
The prop should not feather at idle regardless of oil pressure. The locks will prevent this. Also the prop
Gov does not need much oil pressure from the eng to regulate the prop pitch. The Gov has its own oil pump that
bring the press up to about 250 psi. All the eng has to do is provide oil at any pressure to the prop gov.
Giving the symptoms, and the metal findings and with the eng oil having a hard time reaching the prop gov when its hot, might indicate a very worn out oil
pump in the engine but..........
Also since you had the gov off for a check by the prop shop and it was good , I won't question the gov.... but it also has an internal shuttle type valve
that meters high pressure oil to the prop. When the speeder springs are not matched with the requested prop speed the valve either opens a port to relieve press or opens a port to have more press going to the prop.
If these internals are worn out you will get surging and if they are really worn out and the oil port that is used to dump pressure is very leaky with the oil hot, you can get those symptoms described above.
My thoughts regarding this is when you excersize the prop at 1500 rpm, you are essentially opening up this oil dump port.. doing this you will see your engine oil press also drop because there is now an "open"
path for the eng oil to go, (oil from engine pump to gov oil pump to case)... Sooooo can your prop gov be giving you these symptoms?
I hate to see you have to take the gov back off...... but maybe you will want to anyway and check the screen for metal seeing that you had lots of metal in the filter.

Good luck, and take this above as a layman doing a puzzle solve... It may be way off base, but food for thought.

Gary

Thanks MD11flyer, you may be reading my other post regarding the right engine. It has been surging and we overhauled the gov.

This is a problem with the left engine, and we have not checked the gov in anyway. You bring up a good point that Ive asked several knowledgeable people with no answer. Why is the prop feathering? I thought the locks were supposed to prevent it from feathering.

Prop gov coming apart, dumping the pressure and telling the prop to feather?

Bryan:
Yep read all the posts and indeed see that you pulled the Gov on the other engine. Well that makes it easy, pull the gov on this engine and
be prepared to find another one. These Govenors have very expensive replacement parts and if the metal is from the pump and the shuttlevalve is scored,
you will be looking for a replacement gov. Pull it and keep your fingers crossed, maybe its not to bad. In any case it would be a mixed blessing if you find
this is were the metal is coming from. If the gov turns out to be the culprit, ask the prop shop what their take is on the possiblitity that metal has found its way to the prop.
Not sure what the protocol is in regard to lots of metal in the filter, they will know.
Do you have a oil analysis shop nearby? It probably would be a good idea to have them tell you what and where the metal is coming from.
I say this only because even though the culprit looks very suspiciously like the Gov, there might be other things going on in that engine that you will
want to investigate. (eng oil pump?)

Good luck,
Gary

PS regarding the prop feathering if the prop speed is just above idle and I think that number is around 650 rpm the locks will disengage and allow the prop to feather if oil
press is lost. The locks are only engaged during shutdown at low rpm. If your eng is idling at 900 rpm and you lose oil press in the gov the prop will feather. Don't quote me on the rpm numbers
just giving you the reason for your prop feathering.

Bryan,

Haven't had this experience in 42 years of flying the twin, so like Gary, just guessing at possible causes. I'll be real interested to learn what solves it. Please post so we can all learn.

I know some of you were interested in the resolution.

As it turns out, a small piece of a cam lobe came off and found its way to the front main bearing. It provided a nice hard surface to grind a nice groove in the crankshaft. Those particles trashed the oil pump. The crank particles cut grooves into the oil pump housing. When you start the engine the thick oil passed through the pump normally. When the oil heats up it begins bypassing the pump gears by going through the grooves. Eventually it gets bad enough that slowing the engine means no oil pressure. Since the prop is turning 800 RPM and loses pressure, it bypassed the locks and feathers, this kills the engine.

RESOLUTION: Engine has about 1100 SMOH. Repairing the engine was going to be $10,000. A complete major overhaul is $22,000. I elected to major it.

Interesting! I assume that the crank survived. You are lucky on that front.

Bryan,

Thanks for sharing the source of the problem. How was this eventually found? Any thoughts on the cause? Any advice on something the rest of us can try to avoid?

I always ask these questions when I get something fixed on the twin and the mechanics usually say - things just break and keep flying the way you have been but every once in awhile, there is something else to learn. so thanks in advance if you have advice and if not, don't worry about it.

Sorry that it came to that, but I'd say the decision to major the engine was a good one.

Jay