Oil leak on governor mounting stud

[Browncbr1]

Guys, please consider trying gooping the studs and holes with purple Loctite 515 after cleaning surfaces with acetone or 100LL..

https://www.amazon.com/gp/product/B004H358O4/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

I could not find this locally at any autoparts or hardware stores... So, I bought from the link above.

This successfully stopped the leaks I had at case bolts about 100 hours ago.

Edited October 31, 2016 by Browncbr1

[Bubblehead]

10 hours ago, Marcopolo said:

  The actual original question was if that particular stud hole should be blind or if it should be open to the return oil in the accessory case.  Is it possible that the stud in that position was over tightened thus cracking the base of the hole and creationg this leak?  The fix may still be the same but the origin of the leak and how many it affects would change based on this answer.

 

Ron

Ron, great idea. We are going to redo the stud with Locktite 271 tonight or in the morning. We will look for a crack in that are.  Thank you for bringing this up.  John

[takair]

Aircraft Spruce has a bunch of Lycoming studs.  I think the "P" studs are oversize...just need to match the right stud. I don't have my parts book handy...

http://www.aircraftspruce.com/pages/ep/exhaustcomponents_studs/lycomingstuds.php

Edited November 1, 2016 by takair

[takair]

And a "everything you wanted to know about studs, including locking compound, and more"....article.  Not clear if it applies, but it has good info. http://hhh.gavilan.edu/hspenner/iLearnInfo/AMT100/MaterialProcessHardware/InterferenceFitStudsClass5.pdf

[Piloto]

19 hours ago, Browncbr1 said:

Guys, please consider trying gooping the studs and holes with purple Loctite 515 after cleaning surfaces with acetone or 100LL..

https://www.amazon.com/gp/product/B004H358O4/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

I could not find this locally at any autoparts or hardware stores... So, I bought from the link above.

This successfully stopped the leaks I had at case bolts about 100 hours ago.

Worth trying since it worked on fixing your leak. But I will use PRC 1422 sealant. Has plenty of it and it works very well in fuel tanks.

I noticed that the back end of the lower stud faces the high pressure prop line fitting area. The stud may be facing into a high pressure area rather than an oil return channel. A small pin hole into the stud would cause a substantial leak.

José

[jetdriven]

I'm with Jose, use PR-1422 or similar. Clean the hole and the stud really well with electrical contact cleaner or brake cleaner. Fuel and mineral spirits leaves a film. That prop governor pressure is like 600 PSI, a small leak can pass a lot of oil. 

[carusoam]

From Rob's link...

Check if the studs are interference type threads on the part that goes into the engine block...  these type thread differences make a seal when torqued properly.

It is possible that once torqued enough, the threads compress enough material that the hole is slightly enlarged.  This coincides with the various oversized alternatives.

 

What I learned by reading, the stud isn't supposed to bottom out or shoulder out.  And, an uncountersunk hole is suseptible to cracking...

The link is a good read.  It references lycoming issues.  Could not verify the source of the page (broken link?)

Steel stud threads in aluminum holes can easily move material...

Reminder: I am only a PP, not a mechanic.

Best regards,

-a-

[Guest]

I just re read this thread and the associated SB and SI.  Interesting to note that the Lycoming SI does not specify a torque, Mooney does 80-90 inch pounds which is half of what the Lycoming manual calls out for a 5/16-18 thread.

Clarence

[Bubblehead]

6 hours ago, jetdriven said:

I'm with Jose, use PR-1422 or similar. Clean the hole and the stud really well with electrical contact cleaner or brake cleaner. Fuel and mineral spirits leaves a film. That prop governor pressure is like 600 PSI, a small leak can pass a lot of oil. 

I don't think there is 600 psi.  If there was the flat gaskets would not hold it.  From studying up on this it appears the governor used engine oil pressure and regulates that to the prop.  There is no oil pump in the governor, just flyweights and orifices that line up more or less to raise or lower pressure to the engine. 

Thanks, John

[Bubblehead]

On the advice of the famous "Mahlon" of the Lycoming forum on Matronics and formerly of Lycoming, I have decided to use 271 Threadlocker Red.  I will let you know how it comes out. 

[takair]

Just now, Bubblehead said:

On the advice of the famous "Mahlon" of the Lycoming forum on Matronics and formerly of Lycoming, I have decided to use 271 Threadlocker Red.  I will let you know how it comes out. 

Mahlon is an engine genius.  He used to be at Mattituck in Long Island, NY until Continental moved them.  Had my engine done there and initially had some problems.  Mahlon was instrumental in diagnosing and more importantly covering a tear down at their expense...after it was technically out of warranty.  Not to hijack the thread, but I thought it would be worth the shoutout.  He still has a great reputation in New England.

[jetdriven]

1 hour ago, Bubblehead said:

I don't think there is 600 psi.  If there was the flat gaskets would not hold it.  From studying up on this it appears the governor used engine oil pressure and regulates that to the prop.  There is no oil pump in the governor, just flyweights and orifices that line up more or less to raise or lower pressure to the engine. 

Thanks, John

It certainly has an oil pump inside it and it raises the oil pressure to control prop pitch. I don't know the exact PSI but it's much higher than the 60 PSI the engine runs at. 

http://www.mccauley.textron.com/von_klip_tip_cs_propeller.pdf

[carusoam]

More chemical engineering type thoughts...

1) Govenors use what is called a gear pump to generate the pressure that is sent to the prop.  Gear pumps are what is used when a process needs a combination of high pressure and continuous delivery.  The oil pump for the engine is also a gear pump

2) the control valve controls the pressure that is sent to the prop.

3) the fly-weights operate the control valve

4) high pressure and soft seals don't usually co-exist.  600 psi is pretty high.

5) low viscosity oil is pretty skilled at finding it's way to leak.

6) Loctite red will be a challenge to get the stud out if you don't get it torqued enough to seal it.  

7) Loctite isn't known for it's sealing  properties, is it?  The over-size stud with the interference fit threads is responsible for the seal (and the reason for the torque increasing with tightness). Sure the glue will seal the microscopic spaces after that.

8) not intending to say the stated mechanics above aren't knowledgeable.  More of a make sure you know what they meant.

9) To really know your plane, look up additional information on the governor's operation.  Specifically how your particular one fails when it looses oil pressure.  Most single engine plane's fail with low pressure flattening out the prop.  Some, like the Mooney Missile, will fail with the prop going to a coarse setting that can be challenging during a go-around situation.

10) the manufacturer's web site with your model number is usually pretty helpful.

PP ideas that come to mind. Not a mechanic.

Best regards,

-a-

[Browncbr1]

The purple loctite I mentioned earlier (515) is specifically formulated as flange sealant for these kinds of applications up to 300 degrees.  It does not lock threads as the brand name suggests.   I definitely would discourage use of red locktite 271.  

[cnoe]

As a casual observer it appears that Locitite 515 is not designed for this application. Why would one not use Loctite 592 or its Permatex equivalent which is specifically formulated for such an application? https://www.permatex.com/products/thread-compounds/thread-sealants/permatex-high-temperature-thread-sealant/



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[Browncbr1]

6 hours ago, cnoe said:

As a casual observer it appears that Locitite 515 is not designed for this application. Why would one not use Loctite 592 or its Permatex equivalent which is specifically formulated for such an application? https://www.permatex.com/products/thread-compounds/thread-sealants/permatex-high-temperature-thread-sealant/



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Nice find, that may work better..  indeed the application is different.  My case bolts do not thread into the case.

[Piloto]

I just had my governor tested at the prop shop and no leaks found. One of the shop guys suggested to use baby talc powder to trace the leak source. Any comments on this, I do not want to get cancer.

José 

[mooniac15u]

4 minutes ago, Piloto said:

I just had my governor tested at the prop shop and no leaks found. One of the shop guys suggested to use baby talc powder to trace the leak source. Any comments on this, I do not want to get cancer.

José 

Although a couple of juries have awarded damages there is little actual scientific evidence that asbestos-free talcum powder increases your cancer risk.

[Bubblehead]

jetdriven and carusoam - I stand corrected.  Thank you for sending the link to the booklet.  I learned a lot from that.  I still doubt we're seeing 600 psi but I concede there is a pump.  Oil pressure failure on my plane puts the prop in high-rpm (low pitch) condition.  I may be wrong but wouldn't course pitch be better with engine failure?  When a prop on a twin is feathered it is move through course settings until it is in the low drag position.  Good conversation starter.

Piloto - Good that you had it tested but don't forget to install the plate! I also had mine tested at a prop shop and there were no leaks although my relieve valve was relieving a bit low and they adjusted that.  And baby talc is ok unless you use it frequently in places it doesn't belong.  A lot of people raised a lot of kids using it before putting the diaper on without problems.

General comments on several posts.  First, thanks for all the great information and even the opinions.  I am considering it all.  Since the leak is not between flanges, flange sealant is not appropriate.  I would have liked to get an oversized stud plus some sealant but I could never find any.  I strongly considered and even bought Permatex thread sealant, but Mahlon, who I trust, recommended Loctite Red 271.

Regardless, the evil deed was accomplished last night prior to the start of Game 6 of the World Series.  Go Cubs!  Anyway, the stud is reinstalled with 271 and we'll put the governor on in the next couple of evenings and do a leak test.  I will report back.

I really do appreciate the opinions and thoughts.  That's how I learn. I take none of it at face value, and think it through for myself and then accept and live with and overcome the consequences.

[Piloto]

Why the spacer is important:

http://www.cessna.org/documents/public_info/saib/saib-ne-06-08.pdf

Without the spacer the governor shaft may touch bottom before the gasket is fully compressed. This explains a lot of what I have seen, specially attaching nuts getting loose. This should be an AD.

José

[ArtVandelay]

I just had my governor tested at the prop shop and no leaks found. One of the shop guys suggested to use baby talc powder to trace the leak source. Any comments on this, I do not want to get cancer.
José 

Somewhere I heard athletes foot spray works, easy to apply and it's powdered, never tried it myself, YMMV.

[Andy95W]

58 minutes ago, Bubblehead said:

Oil pressure failure on my plane puts the prop in high-rpm (low pitch) condition.  I may be wrong but wouldn't course pitch be better with engine failure?  When a prop on a twin is feathered it is move through course settings until it is in the low drag position.  Good conversation starter.

With engine failure, yes, but they designed it so that if you have either a governor failure or oil line rupture, you can still make engine power with the prop at low pitch. (No chance of that at full coarse pitch).

[jetdriven]

23 hours ago, Bubblehead said:

 

Put  UV dye in the oil and find the leak after running a few minutes with a black light. 

[Guest]

2 hours ago, Piloto said:

Why the spacer is important:

http://www.cessna.org/documents/public_info/saib/saib-ne-06-08.pdf

Without the spacer the governor shaft may touch bottom before the gasket is fully compressed. This explains a lot of what I have seen, specially attaching nuts getting loose. This should be an AD.

José

Just what we need, another AD covering poor maintenance.  It's been a Lycoming SI for at least 11 years and it's in the maintenance manuals and parts books.  People are allergic to reading.

Clarence

[Piloto]

3 hours ago, M20Doc said:

Just what we need, another AD covering poor maintenance.  It's been a Lycoming SI for at least 11 years and it's in the maintenance manuals and parts books.  People are allergic to reading.

Clarence

At the next oil change check to see if the spacer is there. The spacer is made of metal and can be seen in between the gaskets. The overhaul shop didn't put in there. I found out because of the oil belly stains. Otherwise you may find out when the oil pressure drops to zero. 

José