Grease or Oil on Back of Prop Blades - Now with Pics!

[Deelee]

Got an interesting one, here. Wanted to see if anyone has had similar experiences or can suggest possible causes. And yes, we are going to get this checked out soon - Annual is close.

Some background - bought this '69 Arrow in June 2020. Just before we bought it, previous owner had the prop sent sent out for overhaul. Prop is a Hartzell. There is a note in the logs that the prop was deemed un-airworthy due to excessive grease leaking at blades early May 2020. The prop log indicates that the propeller was sent out, overhauled and the governor was overhauled, as well in May 2020. The Aircraft log notes that a new hub was installed when the prop and governor came back. Also in May 2020.

Fast forward to October timeframe this year. After a flight (about 60 hours after we bought it) We noticed a few streaks of what we thought was oil on the back sides of the propeller blades. No real cause for concern, but we decide to keep an eye on things. Fast forward to this past weekend (about 80 hours after purchase and the aforementioned overhaul/hub replacement). I flew for about an hour. Upon landing, I noticed a fairly large stain on the back side of the propeller blades. When I touched it, no oil came off on my fingers... but it was slick to the touch... greasy feeling.

After lots of internet searching, looks like possibilities include:
Prop seals going bad. This is the one that really rubs at me.... should this happen to a prop that was OH'ed less than a year ago and a new hub installed less than a year ago?

Grease 'burping' out of the zerk fittings - Not sure if this is possible knowing how a zerk fitting works.... but some people seem to think this could be a cause if excessive grease was put in... But why would this happen all of a sudden?

Oil from engine - this one is intriguing since we do have some very small leaks that we haven't tracked down yet. Possibly case bolts that need tightening. Or maybe engine seal?

Something else - When I flew on Saturday, it was probably the coldest weather this aircraft has flown in. Does cold weather affect the seals somehow where they would contract enough to let a little grease out and cause this?

And yes, I am an idiot and didn't take pics after putting the plane away. I will try to get some later in the week when I go to the hangar to do some other tasks. It looks sort of like this (stolen from a post on mooneyspace. The stain looks sort of like this....our prop condition is about 100 times bettter than this one):

 

[Bill]

Any spittle on the windscreen when you cycle the prop before flight? Everyone knows the three things to check for when cycling the prop during runup: oil pressure drop, rpm drop, mp increase. My old crusty CFI also taught me to do one pull while just looking at the windscreen. If you see any misting and/or droplets, the seals are leaking.

I think your seals are leaking, and you need to find out exactly what was done when the DPO had the hub rebuilt. We sent ours out for reseal once, and it started leaking six months later. It turned out that it not only needed a reseal, but a rebuild as the blades had too much play and that damaged the new seals.

 

[Deelee]

Hi Bill,

I was taught the same thing - do a runup with three pulls of the prop lever.... the third is to check for oil on the windscreen. Didn't see any during runup, but I will have to check the windscreen when I get back to the plane. Didn't see any in flight, but it was dark when I got back... so maybe there was and I just didn't notice if there were only a few drops? Anyway it wasn't anything that I was able to notice in flight.

When the prop/governor were sent out, the hub was replaced, too. So it wasn't rebuilt - it was new. But sounds like you were in a similar situation where you had a similar issue soon after work was done. If that is the case, then we will probably want to have it looked at sooner than later. We are scheduled for annual in mid-March. Wonder if the shop that did the work will do the reseal for free or under warranty if that's what our shop says is the issue...

 

[mondtster]

I’d bet money I don’t have that it is grease and it is getting past the seals. Some hartzell props seem better at grease retention than others. Age can be a factor but I’ve seen some that leak almost immediately after install.

The real question in my opinion is how bad is it leaking? Clean the mess up and fly again and see what happens.

 

[Deelee]

Clean the mess up and fly again and see what happens

Yeah good call. This Saturday, I'll take pics of the stain, then clean it. Then do the usual run-up.... fly the pattern a couple of times and then see what we have. @mondtster interesting that some are better than others at retaining grease. Have you ever seen them leak then stop leaking for some reason? (other than all the grease is out which I would think would be..... bad.)

 

[mondtster]

Yeah good call. This Saturday, I'll take pics of the stain, then clean it. Then do the usual run-up.... fly the pattern a couple of times and then see what we have. @mondtster interesting that some are better than others at retaining grease. Have you ever seen them leak then stop leaking for some reason? (other than all the grease is out which I would think would be..... bad.)

I don’t recall seeing any that fix themselves but it could be over serviced. There is no place for the grease to expand into so if it needs to go somewhere out the seal is really the only relief.

It seems that there are two thoughts on servicing these props. First is don’t touch it and the other is per the manual. The “per manual” ones seem to leak more often but that is probably due to having grease in there to leak.

Clean it, fly it, and see what you get. If it is still leaking I would call the prop shop that serviced it last and see if they have any suggestions.

 

[Grum.Man]

It’s my experience that if it’s oil on the prop blade it’s usually the crank to propeller hub seal. It could have gotten damaged during install. If it’s grease from the hub it usually shows up on the nose bowl of the airplane. Not a golden rule by any means but it’s been my experience. You can send the prop off for a re-seal. I would think they would do it for cost of the seals given how recent it was.

 

[mondtster]

It’s my experience that if it’s oil on the prop blade it’s usually the crank to propeller hub seal.

Ive seen very few that leak there and fewer that cause what the OP is describing. Not saying it can’t happen, it just isn’t what I would consider likely. At least not on a hartzell you’d find attached to a Lycoming on an arrow.

 

[Jdm]

Most have suggested to call the prop shop being it was freshly overhauled. I agree, but I’d consider possibly having your maintenance shop make that phone call on your behalf. I just think it’ll go smoother that way. It’s been my experience that overall shops tend to accommodate the installing mechanic more so than the customer during such a situation. The mechanic will probably end up dealing with them anyway at some point, unless you happen to be doing the R&R yourself.

 

[Clip4]

I would pull out the prop logbook and determine when the last overhaul occurred. Seals get hard with age and leaks begin. You can opt for new seals vs an overhaul in some cases.

 

[Deelee]

The prop and governor were overhauled and brand new hub installed in May 2020. About a month before we bought this airplane. And that was in FL... we are in VA. So, if it does end up being an issue with the prop/seals, not sure if our shop is going to send it back to FL for them to look at or what. If it is an issue with the prop that was overhauled so recently... that will be irritating to say the least.

One other thing we are thinking at this point is that it might be oil - we do have some nagging leaks we are chasing down. Someone said it might be the case bolts. Or that somehow this was a one-time event and prop grease snuck out and got on the back of the prop... just odd that that would happen all of a sudden at about 80 hours of flight time after OH.

 

[Jdm]

I doubt your common engine oil leakage is making it’s way out to the prop blades. It could possibly be a crank shaft seal, but my guess is it’s coming from the hub.

 

[Clip4]

The prop and governor were overhauled and brand new hub installed in May 2020. About a month before we bought this airplane. And that was in FL... we are in VA. So, if it does end up being an issue with the prop/seals, not sure if our shop is going to send it back to FL for them to look at or what. If it is an issue with the prop that was overhauled so recently... that will be irritating to say the least.

One other thing we are thinking at this point is that it might be oil - we do have some nagging leaks we are chasing down. Someone said it might be the case bolts. Or that somehow this was a one-time event and prop grease snuck out and got on the back of the prop... just odd that that would happen all of a sudden at about 80 hours of flight time after OH.

The seals in the hub are under high pressure. A scratch that is only visible under magnification to a seal or a part can allow the leak. The prop shop will disassemble and inspect with the goal of finding the culprit. Could have been a defective part or seal before assemble or a seal /part was damaged during assembly. Oil or grease on the blades near the hub is not a crank seal leak.

Call the shop that did the overhaul first.

 

[Deelee]

The first two show the grease on the blades. The third shows oil in the base of the ring gear....

Long story short after sending these to the A/P. He wants to have us fly it over (it is ok to fly a short hop). Probably going to end up replacing the crank seal. He also said that the staining may be caused by the prop grease breaking down and the residual oil leaking out. This makes sense since I called the prop shop that did the overhaul. The asked if we ever did the 10 hour servicing after the prop was reinstalled. Hmmm......... well no. We bought the plane after the previous owner had put only about 2 hours on the prop. So something got lost in the transaction and we never got the handoff that we should do the 10 hour servicing...

Both the prop shop and our A/P weren't alarmed, but they did say it should be greased (per the service manual) as soon as possible. Imagine that the old grease in there broke down and that's why the oil is coming out.

Prop shop also said it may be a pinched seal. If that's the case, they indicated they would take it back and fix it even though it has about 80 hours on it.

At the end of the day, it's getting dropped off tomorrow for further investigation and, most likely just new crank seal and prop servicing. We'll see....

 

[benyflyguy]

Geez that looks like a lot of oil!!

 

[Deelee]

Geez that looks like a lot of oil!!

I agree. A&P does, too. Crankshaft seal is the suspect. They gonna look at it tomorrow or Friday.

Wonder if that is the primary cause of our oil leaking....

From the other angle:

 

[Clip4]

Just understand you could have two issues occurring there.

 

[PaulS]

Nothing a few thousand dollars won't fix. Glad you are having it fixed.

 

[Deelee]

Just understand you could have two issues occurring there.

Yep. That's what we discussed when the A&P saw the pics. One is the oil in the ring gear. That is most likely the crankshaft seal issue. The other is servicing the prop (the issue with the grease/oil on the backside of the prop blades). Could be the seals, but he wants to try re-greasing. This was confirmed when I talked to the prop shop on the phone today, they said it should have been serviced (regreased) after 10 hours on the OH'ed prop. The OH was done just before we bought this plane and we now have about 80 hours on it. He wasn't terribly concerned, but said to have that done as soon as practical.

A&P thinks the grease may have broken down some and the resulting oil (from the prop grease?) is leaking past the seals... He's going to service (regrease). He will also check the seals. If the seals are pinched, then the prop will come off and the prop shop will reseal.

Nothing a few thousand dollars won't fix. Glad you are having it fixed.

quote from our repair shop was three or four hours labor for the crankshaft seal and service prop and check seals. Always possible it will be in the multiple AMUs, but in this case signs don't point to it. Prop shop is willing to stand by their work on the overhaul, too. So if there are issues with the prop, they will take care of it. Hoping it isn't that since we will be down for a longer period of time, but hey.... whatever it takes to get it fixed right?

 

[flyingron]

MAKE SURE he knows how to grease a Hartzell properly. You don't just put the grease gun to the zerk and pump in. This is WHY these props throw grease to begin with (though even if done right they will a little). The Hartzell manual tells you to remove one zerk and pump into the other until you just start to see grease emerge from where the one you removed. (Don't forget to put it back).

 

[Deelee]

MAKE SURE he knows how to grease a Hartzell properly

Great point. I will make sure they do it the proper way. I read Hartzell manual 115 and watched this video -

Mark from Hartzell does a great job showing how to remove one zerk and then pump in the other until grease comes out of the one that was removed. Great acting in this video, too...

 

[Bill]

So why not just put in one zerk and a plug on the other side? Makes it pretty apparent on how to do the job.

 

[mondtster]

So why not just put in one zerk and a plug on the other side? Makes it pretty apparent on how to do the job.

Why stock another part and make another part number when a grease zerk plugs the hole fine?

A plug in the hole would not make it any more apparent that It needs to be removed to grease the prop than having two zerks in my opinion. A mechanic or owner would just see the zerk and go to town without realizing the plug also needs to be removed.

 

[Bill]

Why stock another part and make another part number when a grease zerk plugs the hole fine?

A plug in the hole would not make it any more apparent that It needs to be removed to grease the prop than having two zerks in my opinion. A mechanic or owner would just see the zerk and go to town without realizing the plug also needs to be removed.

OK, I'll roll with the BOM reduction, and true, boneheads can still botch the job. I do all the work on my own vehicles, but I've always bought the FSM for whatever it is I own. Reading how to do the job before commencing prevents much heartache.

 

[mondtster]

OK, I'll roll with the BOM reduction, and true, boneheads can still botch the job. I do all the work on my own vehicles, but I've always bought the FSM for whatever it is I own. Reading how to do the job before commencing prevents much heartache.

Agreed on the service manual. I do however think you’ll find that many mechanics think they know how to do a job and do not review the manual first. Especially since owners are always beating on the mechanics to do the job cheaper and faster.

Manual or no manual it is in people’s best interest to truly understand the system that they’re working on. I have only met a handful of people who really do. If more did, we wouldn’t have all the stupid theories on how/why stuff breaks that we do.

 

[Arrow76R]

I had a very similar experience with my '69 Arrow back in 2008 (as I recall). Had flown to OSH and was almost home but stopped about 100 nm away to drop off a friend. It was HOT and as I did a quick pre-flight for the short trip home I noticed what looked like fine grease on the right side windshield. A look at the cowl showed more just under the prop. The prop blades showed a greasy residue too. Called my mech who said to clean the prop blades and run it up. I did and more grease, definitely NOT engine oil. Flew it back home (staying over roads!) and went directly to the shop. Mech pulled the prop and sent it to a prop shop. Verdict came back that the hub was shot and the blades were not any better. So new prop and hub. Decided to send the governor away to have a small leak fixed...verdict was "the case can be re-used" but everything else was shot. SO...$14 AU later, I had a new prop and governor...

 

[Jdm]

You don't just put the grease gun to the zerk and pump in. This is WHY these props throw grease to begin with (though even if done right they will a little). The Hartzell manual tells you to remove one zerk and pump into the other until you just start to see grease emerge from where the one you removed.

I didn’t realize there was any other way to grease a prop hub. We always pulled one zerk and pumped new grease through the remaining zerk until clean grease begins to come out the open hole. You’re not trying to just top it off. You want to purge out the old dirty grease.

 

[Deelee]

$14 AU later, I had a new prop and governor

Ouch. Guess the good thing here is that prop and governor were OH'ed less than 100 hours ago (in May 2020) and the hub is new as of May 2020... So if it is a situation where the prop/hub/governor are shot, this will go back to the shop where the work was done. I actually have had phone conversations with them and they said they will stand by their work if it comes to that (they are pretty sure it won't).

Dropped off this evening at the shop where we have our work done. They are going to look at it in the morning.... we shall see...... (The waiiiting is the hardest part....)

 

[Deelee]

well, they didn't get to bring it in to the hangar to look, but the A&P did take a peek on the ramp. The prognosis is still most likely crankshaft seal needs to be replaced - that will fix the oil leaking into the ring gear.

The thought on the prop staining is that the prop grease may have broken down and the resulting oil leaked out past the seals. Initially, the A&P says this may result in the remaining grease 'caking'. And this would mean the prop has to be sent off, seals removed, caked grease cleaned out, resealed and then re-greased. Which means the prop may have to go out to the prop shop afterall. Not sure yet since they haven't taken the prop off to check, so there is still hope that we won't have to have the prop sent out. But not looking great at this point. Ugh.

We'll see next week when they can get the plane in the hangar to take a proper look.

 

[guzziguy]

Yup. Been there.

69 Arrow with a newly OH'd prop and governor:
Found streaks on the back side of the prop, couldn't understand how a newly OH'd prop/gov would have ANY issues.
A&P investigated. There WEREN'T any issues with the prop or governor.

Turned out the small oil leak I had on the engine (which I hadn't been able to trace at the time) was causing the streaking. The A&P explained that, due to airflow around the engine, it was very likely that it was the oil from the engine getting blown FORWARD onto the back of the blades.

Who'dathunk?

As follow up, it's been two years with no issues on the prop/governor, no oil/grease on the windshield and, lo and behold, we found the leak a couple months ago: no more streaking.

YMMV

 

[Deelee]

@guzziguy Thanks for the reply! This will give me enough hope to survive the weekend

What did the A&P have to do in order to determine it wasn't an issue with the prop/governor/hub? And do you remember where the engine oil was leaking? In our case, the crankshaft is the culprit. There is most certainly oil on the inside of the ring gear (the one with the teeth)... check out the pic I posted above. Wonder if there is a chance that, like in your case, that oil is getting flung forward and staining the prop and getting tossed back on the windscreen...

Thanks again for the post... hope springs eternal...

 

[guzziguy]

As I recall, he stated that a minor streaking on the back side of the blades was actually quite common and he didn't really DO anything to confirm that was the case, it was just something he was aware of being possible (oil being flung forward).
There were a couple leaks, but the one that I remember specifically was on the TOP of the engine. Not sure what they're called, but they are the two tubes that run on top of the cylinder (I think they have something to do with the valves). One of those tubes was loose.
Anyway, long story short, you're probably ok. I can send you the mech's contact info if you like to get more input from him.

 

[Deelee]

two tubes that run on top of the cylinder

Pushrod tubes! Yeah, those are a common source of leakage. We had a weeping there that was addressed... but may have come back. Check out the pics up there... were your oil streaks that bad though?

 

[guzziguy]

Your streaks looked very much like mine.

 

[Deelee]

Your streaks looked very much like mine.

You have given me the hope I need to sleep through the next few nights before they can take a close look and tell me all that is needed is to replace the crankshaft seals (3-4 hours labor and a $5 seal). I would be such a happy man.

 

[guzziguy]

Glad I could contribute to a good night's sleep.

Of course, while they're fixing the crankshaft seals, they'll discover the crankshaft needs to be replaced...
But hey, one crisis at a time, right?
And don't forget, it's just a hobby. Putting off retirement to your 80's is part of the fun.

 

[Deelee]

they'll discover the crankshaft needs to be replaced

Aaaaannnndddd there goes the good night's sleep..... d'oh

 

[kontiki]

Something a friend showed me, anytime I'm pre flighting an airplane with a CS prop, I manually try to rotate each of the blades to make sure there isn't any excessive play. It takes a sec.

 

[guzziguy]

Aaaaannnndddd there goes the good night's sleep..... d'oh

Any update?

 

[Deelee]

Any update?

They didn't get to look yesterday. I called today and the manager said they were going to pull 'er in today (before lunch she said) and start looking. Didn't hear back by end of day. So no news. I'll call again tomorrow morning for an update. I never know if no news is good news ("Oh... yes, we fixed everything and she's ready to be picked up!"), bad news ("Oh... yeah.... we found a bunch more stuff that we don't even know what to do with, so we are calling experts and it is taking longer than we thought....") or no news ("Oh, yeah, we had to pull in a King Air to fix a tire and it took longer than we thought... sorry... we'll look at yours tomorrow")...

so hopefully news one way or the other tomorrow.