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DXB

M20C - another prop governor thread

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My Hartzell H-1 governor was last overhauled 22 years and 2000hrs ago and has been trouble-free in the 4 years I've owned the plane.  Now 2 things are happening:

1.  An isolated vertical streak of oil appears on the firewall behind the governor after a couple hours of flying - this is only a small leak that has been pretty stable for a few months.

2. On two occasions during this period, the prop cable has developed resistance when trying to pull it out during runup, with no resulting rpm drop.  This issue resolved on its own both times after fiddling with it. I am very suspicious that it is the governor arm causing the resistance and not the cable itself that is binding. I've had no issues like this in flight.

My questions:

1. Based on description above, how sure can I be that the oil leak is from the governor? What part of governor?  My reading tells me it's the seal around the control arm that gives trouble, but I don't see much oil in that area.  There is some oil mess on the underside of the governor, but it's really tight in that and hard to get a clear view. I'd hate to replace the governor and then have it turn out to be something else leaking.  Or maybe just the gasket or mounting screws that need to be retorqued.

2. How urgent is this problem, assuming it localizes to the governor?  Is it a safety of flight issue?  I suspect not.  I am inclined to get it addressed at annual in a 3 months, but would I expect it to stay stable well beyond that?  Or should I freak out and deal with it right now?

3. Replacing with a PCU5000 will cost about 1amu more than than an overhauled H-1.  The modern design seems worth it though from a reliability perspective. Any thoughts on this? Any other options?

I appreciate any input as always!   

Edited by DXB

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Safety of flight comes about in two ways...

1) Losing the seal, and it allows six quarts of oil to depart over time....

2) Loss of prop control... having the prop stuck in a low pitch mode can keep the engine from generating enough power on a Go-around...

 

Locating the leak...

This is tough under the cowl... 

1) clean and use spray powders that are designed for the task...

2) black light sensitive dyes work pretty well...

 

Add to the decision...

1) how many hours on the gov?

2) Last OH?

 

There are three parts of the gov that are going to see wear...

1) fly weight system

2) pressure control valve system

3) gov’s gear pump system...

 

There are several advantages of the new PCU...

1) May be lighter weight...

2) may be smaller...

3) may be more responsive...

 

Check the age of the prop control...

1) 2000hrs... time for a new one... (note specifically for Dev)

2) Original that came with the plane... time for a new one...

3) Looks like it came out of excess stock from WWII... time for a new one...

 

While you are in there... review the age of the other engine controls too...

New controls, and the standard order across the panel, is pretty nice...

PP thoughts only, not a mechanic...

Best regards,

-a-

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6 hours ago, carusoam said:

Safety of flight comes about in two ways...

1) Losing the seal, and it allows six quarts of oil to depart over time....

2) Loss of prop control... having the prop stuck in a low pitch mode can keep the engine from generating enough power on a Go-around...

 

Locating the leak...

This is tough under the cowl... 

1) clean and use spray powders that are designed for the task...

2) black light sensitive dyes work pretty well...

 

Add to the decision...

1) how many hours on the gov?

2) Last OH?

 

There are three parts of the gov that are going to see wear...

1) fly weight system

2) pressure control valve system

3) gov’s gear pump system...

 

There are several advantages of the new PCU...

1) May be lighter weight...

2) may be smaller...

3) may be more responsive...

 

Check the age of the prop control...

1) 2000hrs... time for a new one... (note specifically for Dev)

2) Original that came with the plane... time for a new one...

3) Looks like it came out of excess stock from WWII... time for a new one...

 

While you are in there... review the age of the other engine controls too...

New controls, and the standard order across the panel, is pretty nice...

PP thoughts only, not a mechanic...

Best regards,

-a-

Anthony- well that sure makes me want to replace it ASAP :blink:!  I think these governors generally fail to fine pitch tho and overspeed, not course pitch and limit power

 I’m wondering aloud how likely the catastrophic failure modes are (i.e. no oil, and/or engine overspeed) .  I guess one would have to know exactly where it is leaking and why to answer this question.  It’s awfully tight in there for me to figure it out, so I’m wondering what standardly leaks on these governors. I’ll also feel stupid if the leak has nothing to do with wear of the governor.

I’m  moving toward ordering a PCU5000..any other parts I should buy along with it.  My mags are due for IRAN so probably easier to do the governor at the same time.

 

 

 

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2 hours ago, DXB said:

  I think these governors generally fail to fine pitch tho and overspeed, not course pitch and limit power

 

Yes, when the govs are working properly... they will fail to fine pitch.  Except for Missile and Rocket...  the blades will land on the stops... if set correctly, the stops should minimize the possibility of overspeed...

But, when it comes to a stuck control, it is generally stuck at the last rpm it was at while working properly... possibly at cruise rpm or descent rpm if you use one...

...which can leave you missing 10-20% of total hp.

 

Depending on engine laws of physics... high power, and low rpm may not be acceptable under some cases...

More of an OWT, but you don’t want to find out during a go around that the engine is suffering from pre-ignition... the pistons experience a melt down if this is to occur...

Most probable source of oil leak is most likely around the old seal between the engine and the gov... you might find that there is also a spacer in there making seals more complex and leaks even more possible with time in use...

Next would be where the control shaft is sealed as it penetrates through the gov’s case...

 

I think the cost of OH for the gov is a very similar price to a new PCU.... so, many MSers have gone with the new device.

See if that clears up my thoughts any...

As usual... these are only PP thoughts, not a mechanic...

Best regards,

-a-

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@DXB  I have a half bottle of AC Delco 10-5045 fluorescent dye and a UV flashlight that I used to find a leak on my motorcycle.  I don't know if that dye is ok for aircraft engines, but it is designed to be used in engine oil to find leaks.  If anyone knows if that is ok to use, I can drop it off at your hangar. 

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8 hours ago, cferr59 said:

@DXB  I have a half bottle of AC Delco 10-5045 fluorescent dye and a UV flashlight that I used to find a leak on my motorcycle.  I don't know if that dye is ok for aircraft engines, but it is designed to be used in engine oil to find leaks.  If anyone knows if that is ok to use, I can drop it off at your hangar. 

Thanks Chris - I suspect it's just fine - however the governor is so poorly accessible i doubt I could reasonably do a dye penetrant inspection without major invasive work first.  

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The oil dye goes in where you add a quart of oil...

If it comes out... you have found your leak...

Probably won’t take too many minutes of engine run time before the first hints become available...

Too much time, the dye is everywhere like the original oil leak...hard to find the source...

+1 for knowing the dye is O360 compatible...

Best regards,

-a-

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13 hours ago, carusoam said:

The oil dye goes in where you add a quart of oil...

If it comes out... you have found your leak...

Probably won’t take too many minutes of engine run time before the first hints become available...

Too much time, the dye is everywhere like the original oil leak...hard to find the source...

+1 for knowing the dye is O360 compatible...

Best regards,

-a-

Ah I get it now - might be worth a try with stuff that's known to be safe for aircraft engine oil.  My rudimentary understanding is that Aeroshell itself fluoresces under UV, but I guess that wouldn't be useful without cleaning off every last bit in advance, which might be near impossible on the governor without removing stuff that's in the way.  I see this product when I google https://www.grainger.com/product/39D696?gclid=EAIaIQobChMIspuF-rPn5AIViNlkCh3fXQ9dEAYYASABEgJCN_D_BwE&cm_mmc=PPC:+Google+PLA&ef_id=EAIaIQobChMIspuF-rPn5AIViNlkCh3fXQ9dEAYYASABEgJCN_D_BwE:G:s&s_kwcid=AL!2966!3!264955915910!!!g!437513351039!.   However it needs a serious high intensity UV lamp for excitation (~1.5amu), not a cheap $15   395nm flashlight.    Anyone know how to accomplish this cheaply?

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RJ,

Is what you have on your M20C the Hartzell govenor?

There are a couple of ways to know possibly...

The POH May list all the details of what is included with the plane... from the early days...

There is an FAA doc that has all the tech details of all the M20s built over the years...

Your log books will have the records of any hardware that has been changed out over the years...

You can look at it to determine what it is...

You can take a pic and post it here... and see if anyone else recognizes it...

There aren’t many options I can think of after that...

Best regards,

-a-

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16 hours ago, Rjfanjet said:

I have a 68 C. Looking to replace the governor with the PCU5000. Is it the Hartzell style?

Theres a ton of PCU5000 variants - just use their application chart - there is only 1 correct choice for your engine.

I’m still trying to figure out what is the right thing to do about this btw - i.e. keep watching small oil leak or go ahead and replace 21 year old Hartzell H-1.  The oil streak on the firewall is right behind the governor, but I still cant be sure it’s the governor that is leaking.  I will be upset if I do the replacement of an otherwise perfectly functional governor and still have the leak.  And discretely identifying the leak seems like a non-trivial task.

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I have the H-1 as well. I had a clear leak and sent it out to Air Prop Specialists in Marainna, FL. I wanted an IRAN versus an overhaul. Came back with new seals and a note that everything else was within spec for $350.

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I had a similar.leak from the base of my H1 governor that appeared after the installation of my newly overhauled engine. TT on the governor was 500hrs. Took no chance and sent it to my favorite prop shop. Picked it up yesterday and it tested good with no leaks!  The prop specialist changed the shaft o-ring and two gaskets for the reinstallation and told me that it also needed an aluminium gasket, supplied by Lycoming, to support the paper gaskets, which wasn’t present when we took it off.
Anybody familiar with that part? @M20Doc or @Cody Stallings

https://www.lycoming.com/sites/default/files/Propeller Governor Pad Plate PN LW-12347.pdf
 

 

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