Teach Me About Prop Governors

NealRomeoGolf

NealRomeoGolf

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I landed today and saw oil on my cowl. And what I thought was dirt on the windshield from dried rain must have been oil too.

So what are the failure modes of prop governors? What would happen if all the oil went? Why do they leak? Simple gasket change?

Waiting to hear back from my mechanic. Sent him pics. Yay airplanes.
 
My first question would be, why do you suspect the oil is coming from the governor? I'd be more inclined to be suspicious of the prop.

Based on my experience, governors generally don't cause much trouble. There are a few gaskets and o-rings that might leak in them but that doesn't seem to be a common problem. I've seen governors cause RPM hunting problems far more often than I've seen leaks from them.
 
mondtster said:
My first question would be, why do you suspect the oil is coming from the governor? I'd be more inclined to be suspicious of the prop.

Based on my experience, governors generally don't cause much trouble. There are a few gaskets and o-rings that might leak in them but that doesn't seem to be a common problem. I've seen governors cause RPM hunting problems far more often than I've seen leaks from them.
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That's just me being a rookie. This is my first constant speed prop. Time for me to learn.
 
If it’s greasy it’s probably coming from the prop hub itself. There’s um.... seals and stuff. :)

We had a small period of time where ours would put a little blob right on top of our cowl. More like “mini streak”. Always in the same spot.

Found a service bulletin on our specific prop setup that said it was often caused by not “deep exercising” the prop far enough and the seals drying out a bit as long as it was a very small amount.

Added an occasional very low RPM full cycle to the prop during preflight, stopped happening.

But it can be worse / actual busted seals / whatever.

We attempted the instructions of the SB under the watchful eye of our A&P who wanted details. Modern camera phones took care of that.

Ours hasn’t done it in years since we “exercised” more.

In conjunction with that we also started looking up costs for a prop IRAN and found most places just find it more convenient these days to do the full rebuild for a set price, assembly line style. Wasn’t TOO awful in AMUs for ours...

But we didn’t have to go there. YMMV.
 
Not sure about the whys, but ours started talking to us by leaving rivulets of oil on the blades after shutdown. Took it in for o/h but it was too far gone, ended up getting a new-to-us prop.
img_0306-jpg.46132
 
By the way we also learned in that process that case and front main seals on the engine block itself or other leaks far enough forward can be “sucked out” with certain cowl shapes and deposited on a specific location. That’ll look like oil and not grease.

We didn’t have any of that going on but I’ve seen where a messy oil change left a film all over things (owner didn’t wash the engine off) and he had little dirty oil streaks for a few flights in a specific spot on top side of his cowl from the mess he made, as it collected and blew around.
 
I hope it’s not as bad as I fear it is from your description. :(
 
Here are the pics.

The smudge in the oil is from my finger seeing if it was what I thought it was.
20201001_143107_lowres.jpg

There was also oil on the back of the prop blades. You can see the spattering on the cowl too.

20201001_143125_lowres.jpg
 
Since you asked for an education, if that’s oil, it’s the same oil keeping your engine lubricated, so that’s a big deal. Personally, I would not fly it until a mechanics inspects in person, and in my layman’s opinion, you’re going to need some prop hub work.
 
If you can stomach another non-A&P opinion.

The oil servicing the prop is from the engine, which is why you cycle the prop during runup to get nice warm oil going through it. If that oil is "escaping" somehow you're headed for trouble.
 
NealRomeoGolf said:
Here are the pics.
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I'd say with 95% certainty that the pictures are showing grease that is being thrown from the prop hub. This has nothing to do with the governor.

I haven't seen one fix itself yet either. You're likely headed toward a prop shop visit.
 
Spinner will need to come off for a detailed inspection of the hub and blade roots. Also the engine oil seal.

Just had to deal with a similar issue. A new seal kit was installed and no more drips and mess.
 
Sorry, piling on. Ours was nowhere near that bad.

Looking like an inspection to figure out what’s leakin’...

Sorry man. :-(
 
JAWS said:
Spinner will need to come off for a detailed inspection of the hub and blade roots. Also the engine oil seal.

Just had to deal with a similar issue. A new seal kit was installed and no more drips and mess.
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That sounds much cheaper than what mondster sounds like he's saying. Hope you're right.
 
NealRomeoGolf said:
That sounds much cheaper than what mondster sounds like he's saying. Hope you're right.
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I think his post is misleading. That "seal kit" was likely for the prop, which is something outside the scope of what a typical aircraft mechanic is capable of handling.

But, you might get lucky and have it end up being the o-ring that seals the prop to the crankshaft flange. I haven't seen a leak there manifest itself in this manner though.
 
A friend's Cessna 177B did similar, the crankcase nose seal was completely loose from the crankcase and spinning with the crankshaft. R&R the constant speed prop is probably the crappiest part to fix that.

But what you have looks like its the prop itself to me. Take the spinner off and look.
 
NealRomeoGolf said:
All good. At least it happened at home rather than while I was in Boise.
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Aside from the massive inconvenience, you would have been in good hands, there's an excellent prop shop on the field...
 
Gonna pull the fuel tanks while it's down?
 
So guys, what happens if the prop loses all its grease? Bearings seize and the prop stops? Trying to understand what the failure mode is.
 
You updated the thread to indicate the prop needs to be pulled (sorry to hear that...but better safe down here!).

I thought I had a prop problem and started with the governor. I had never given it much thought but it turns out the governor is on the side of the motor, not directly on or within the prop assy. You have probably found this out as well.

I am curious - did they also pull the governor or did that stay on the engine? Since it (governor) is not suspect I wouldn't expect them to pull it but I have zero clue if they normally pull both and when the prop is pulled and repaired/replaced.
 
The governor wouldn't cause this. Might be a good time to check the logs and see if it's due for an overhaul though....
 
Salty said:
The governor wouldn't cause this. Might be a good time to check the logs and see if it's due for an overhaul though....
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Already understand the governor is not the issue. Just wondering if props are normally serviced independent of the governor or if both are usually worked together.
 
Sinistar said:
Already understand the governor is not the issue. Just wondering if props are normally serviced independent of the governor or if both are usually worked together.
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I don’t know why they’d be tied together, but if one needs work, and they were both worked on at the same time last, might want to have them both looked at....
 
And what about the governor specifically?
 
450 hours is not a lot of time on a prop governor but if the governor goes bad in flight it likely will take the prop to low pitch and typically an engine does not generate enough power to maintain level flight, i.e. you are going to land even if you don't have an airport near your position. It is usually recommended the prop governor gets overhauled when the prop does.
 
Briar Rabbit said:
450 hours is not a lot of time on a prop governor but if the governor goes bad in flight it likely will take the prop to low pitch and typically an engine does not generate enough power to maintain level flight, i.e. you are going to land even if you don't have an airport near your position. It is usually recommended the prop governor gets overhauled when the prop does.
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It's not the governor. It's just grease from the prop itself. I was wrong about the governor thing.
 
NealRomeoGolf said:
It's not the governor. It's just grease from the prop itself. I was wrong about the governor thing.
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I understand and it is obvious it is not the governor, but you did ask about governors. Just wanted to share info about governors and the importance of overhauling one even if it is working just fine.
 
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