Lose of Prop control-Lycoming 540-1990 Money Bravo

[Dklossner]

Looking for ideas and possible causes, below is the details of the incident. 

On January 2^nd 2011, at level flight at 4,000 ft, 27 inches MP @ 2,400 RPM, OAT -4c.  The RPM’s starting creeping up, in fact is exceeded the redline by 200 RPMs.  I started pulling out the prop control, but it had no effect.  Then I started reducing MP pressure even farther to 20 inches – only then did the RPMs start to decline.  We flew the remainder of the flight, approximately 10 minutes,  at 20 inches MP @ 2,500 RPMs.  When we landed, we conducted anther run up and again the prop showed no signs of pitch variation regardless of the prop control position – it was like the prop control linkage had broken, which of course was not the case. 

 

On January 3^rd, we removed the prop governor – had it tested and it tested good

 

On January 5, we conducted the leak test in accordance to Lycoming service instruction 1462A ,  It failed the test, which is a indication of a internal engine issue.  I am following the Lycoming SB 396K for overspeeds.

 

Currently the TT is approximately 1,974 - 145 hours SMOH, which was done in 2006.  The engine has had oil changes ever 25 to 40 hours.  There has been no noted issues with any maintenance and the engine has ran strong with all engine guages in the green – last annual was completed in November 2010.  Oil samples show no signs of excessive wear and oil filter inspections are clean.  All compressions are excellant.

 

I have contacted the engine rebulder and we have started dicussing repair options - I will see how this goes, right now he is reluctant.

[takair]

David

I saw a similar issue on an E model a few years ago, not quite the same, but the same type of troubleshooting.  I had sent out the governor twice for a check.  On both occasions it checked good on the bench.  That prop shop said I may have an engine problem.  The engine shop insisted it was the prop or governor.  Long story short, I sent the governor to another shop.  It initially bench checked good, but when they tore it down they found all kinds of problems.  Under the right conditions it could not keep up the oil pressure and the prop would go into lower pitch.  The internal damage was enough that the first shop should have seen it.  Feel free to PM me for the shop that got it right.

[MooneyMitch]

As far as governor overhauls, I have had compete success with two overhauls.  One on my former F model and one on Jolie's E model.   Both units were overhauled at AeroSpeed in van Nuys, CA.   These are my experiences only.  I hope your engine internals turn out to be ok.

[carusoam]

Loss of RPM control comes mostly from loss of oil pressure in the prop.  This can be caused by three things.  Two of them are obvious, the third is not.....

[1] govenor, most obvious, does not generate oil pressue to adjust prop.  The govenor also houses the valves that release the oil pressure out of the prop.  You said you took care of this.  I had one rebuilt also.

[2] Oil is leaking out of the system externally.  This would be extremely obvious by the amount of oil on the windshield and excessive CHTs.....Again, not the issue.  I had a prop rebuilt to match my governor.

[3] Oil is leaking uncontrolled inside the system.  This is something I learned from the Canard forum guys with Lycoming engines.  There is a plug in the center of the crank shaft (at the front) that is leaking.  The crankshaft is through drilled.  Prop on one end and open to the crank case on the other.  Oil pressure enters the the shaft through holes in the side by a hose supplied by the governor.  That's the orange silicone covered oli line at the front of the engine.  If the plug becomes unseated, the oil pressure that is supposed to hold your prop angle of attack / rpm is now leaking back unnoticeably into the crank case.

Fortunately the fix is simple.  Remove the prop, inspect the plug and put it back ih place.

My recommendation, if this is the case, is to supply a new plug.  Your mechanic may want to just hammer the old plug back in.  It came loose once, don't let it do it again.

It's a low cost fix to a serious problem.  I only found out how it worked, with enough detail, after I had my prop and governor overhauled.  I now believe in a well balanced prop though.....

Check your engine manual for part numbers.  I am sure you will find the plug in a drawing at the prop end of the shaft.

Good luck, let us know what you find....

Best regards,

[Dklossner]

Guys,

Thanks for your thoughts.  I have ruled out a faulty governor test due to the results of the Lycoming pressure test 1462A. 

The question about the plug is still an concern.  Apparently, according to Lycoming, there are two versions with several different iterations per version (large 1.75 dia. plug & small 1.25 dia. Plug).  The prop shop mechanic was confident that the plug was good and tight.  In fact, he said we had tapped on it with a center punch to make sure it was secured.  Excerpt from the prop shop which conducted the test “The test we performed was the propeller oil control leak test per the attached Lycoming Service Instruction.  Our results from the test were 0 psi (step 7 in the service instruction).  The minimum specified is 6 psi.”

A few more details to consider:

·         Plane has always been hangered and primary flown in warmer climates (used Shell Areo 100+),  I am based in Ohio, so the first thing I did was change to Shell Areo 80+.  I also added the oil additive Cam Guard.

·         I had the prop shop change back to the 100+ (trying to eliminate all the variable).  We now have partial prop control, whereas before we had none. 

Again, thanks for the ideas and feedback

[carusoam]

David,

What you have experienced is governor system failure.  It is unlikely that you have oversped your engine.  When the govenor system fails on your aircraft it fails to max rpm.  You handled it the only way possible, reduce manifold pressure and operate it like a fixed pitch prop until you can put it safely on the ground.  (When the governor system fails on a rocket or missile, they go to full feather, nice idea for max glide if the engine dies, not so nice if it is a simple governor system failure.)

Thoughts to share on your tests and observations...

[1] Partial control is back after hitting the plug back in place?  I believe this plug forms a seal by being properly "hammered" into place.  It's proper operation requires a tight seal.  If it comes out, putting it back in is a good idea, but it will already have been "shaped" by its initial installation.  Shaping it again will unlikely give the proper seal that you are looking for.  I put this up there with crush washers for spark plugs.  Not a good idea to reuse.  The next owner of my plane, unfortunately, reported having to replace the plug again.  My A&P had also reused the existing plug.  These hardly ever fail, so nobody keeps one in stock.  Very few people have experience with it.

[2] Lower number oils are heavier in weight, higher in viscosity, and perfom better in gear pumps than lighter weight oils.  They pump well and leak less.  Change the oil all you want, however, it will not be responsible for the prop control not working.  One might be a little slower to react than the other....

[3] Govenor has gear pump and valves.  Your rebuilt govenor was tested and you got a yellow tag back with that right? I think I understand that you had the existing one tested to these standards at least?  The thought being that the valve system is stuck and the return side of the valve is left open.  The gear pump always operates, the old style spinning regulator adjusts the valve position to either pressurize the prop or leak excess oil to the sump.

[4] In the prop, there are cyllinders that use this pressurized oil to change the angle of attack of the blades.  What is the condition of these cyllinders?  If you pump pressure into the prop, do the blades operate properly.  I don't recall how much oil pressure is required to operate the cyllinders.  Compressed air (regulated, start low first) might work (your A&P will know).

[5] If you were to disconnect the oil supply line back to the governor, pressurize the front you will either operate the prop blades or you will hear the leakage back into the engine block.  Prop shop must have a definitive test for this.

[6] How much does it cost to remove the old shaft plug and replace with a new shaft plug.

[7] New idea - not to be alarming: The shaft seals at the front of the engine block are strong enough to not leak when oil is pressed into the crank shaft.  If the back seal is deteriorating oil does not enter the shaft and leaks back into crank case...This would be a big job.  take a look at your engine drawings and identify what there are for shaft seals at the front....seal bits would/may be showing up in your oil filter.  I have not seen a shaft seal fail on anything but an ancient Chevy...  and again, lighter weight oils would behave worse, not better, with a leaky seal.

I am stuck in Oss, NL for a few days.  I don't have access to the lycoming tests that you have stated or drawings.  If you point me to where they are on the web or email me.  I can take a look at it.  It has been about five years since My M20C experienced this similar challenge.

In case anyone is concerned...The recommendations I have given here are based on my personal experience and learning.  It is up to you and your A&P/mechanic to follow proper procedure.  I am not an A&P.  Just an engineer with some flying experience and a few owner assisted annuals.

Best regards,

-a-

 

[Dklossner]

Below is the ling to the Lycoming SI 1462A which outlines how the test was completed and the expected results. 

http://www.lycoming.textron.com/support/publications/service-instructions/pdfs/SI1462A.pdf

My action plan is as follows:

1. remove prop (this is one of the intial steps required to remove the engine)

2. Double check the condition/seal of the crankcase plug. If possible develope a external to engine pressure check

3. Based on the plug inspection/test - remove engine or be thankful I didn't have to remove engine.

 

 

 

 

[carusoam]

I read the leak test procedure. 

For anyone following along: Remove governor and replace with 1/2" steel plate drilled and tapped for compressed air and differntial pressure gauge (compression test).  Apply 40 psi air to system and read how much air pressure is retained in the system (vs calibrated leak of compression tester).

David indicates 0 PSI retained.  All of the air leaked out.  if the pressure read 40 psi, none was leaking out.  Prop would have been stuck in low rpm.  Acceptable range is 6 to 35 psi.

Looks like a leak in the system.  Now the question is where.  shaft plug or shaft seals sound like the only "internal leak" options.

I would still want to verify two things:  [1] can I hear or perceive the leak when air pressure is applied.  [2] is the prop cylinder activating when pressure is applied. 

[1] Prove to yourself a second time that it is a leak into the engine:

Are you able to apply the air pressure to the system to set up an audible leak.  listen down the oil fill tube?  If air is leaking into the block I would think you can hear it.  Leaky valves are audible in their exhaust pipe during compression tests, for example.

[2] Prove to yourself it is not a prop problem:

It sounds like you have eliminated the prop as a problem already.  Were you able to activate the prop cylinders by pressurizing the system? 

The two bladed props, i believe only has one cylinder?

I don't know how easy it is to test the shaft plug for a leak even with the prop removed.  The crank is straight hole with a plug on one end.  The side oil supply holes will be open to the exterior shaft seals.  You would have to apply pressure beyond the supply holes to test / eliminate only the shaft plug. 

You may be able to test /eliminate the shaft seals by applying pressure (as you did before) to the system and blocking the side feed holes.  It will be difficult to hold back 6 psi of pressure, but if you hold back more than 0 psi, it is good news for seals.

Maybe the front seal is removable to inspect the rear seal?

Maybe the shaft plug can be inspected for shape and condition, prior to removing and replacing.  It is a simple aluminum coin that is compressed in place.  I think removing it is like taking out a freeze plug from an engine casting.  It get's destroyed in the process.  It would be hard to tell if it were the cause after the fact.

If you need to create a test (unlikely): Can you build a shaft size plunger?  a disk that is wide enough to block of the side supply holes and wrapped in a rubber material to create a simple plunger seal.  A little oil to complete the seal and allow for sliding down the crankshaft.

You can use it to block off the supply holes during the compression test on the shaft seals.

You can use it as a simple piston.  Move it down the shaft, it should move easily up to the side supply holes.  After that, it should start compressing air against the shaft plug.  (if it is really plugging that is).

Just some additional thoughts.

Hoping for the best....

-a-

[Dklossner]

I was thinking the same thing,  can we pressure test the plug - externally?  The prop shop did run the prop through its paces and they claim all is well. 

Another thought is how quickly this situation came up - does that give us any addtional clues?  if were a bearing issue, wouldn't I see a lower engine pressures?  If it were a crack - oil leaks?

Thanks again.

 

 

 

[carusoam]

Jose, Jetmech......

Any thoughts....?

 

-a-

[jetmech1972]

I'm sorry cant help on this one.  If the govenor has come back with a yellow tag and have cycled the prop in your own test then I too would eliminate the prop and govenor.  The logic of the posted test procedures I would agree in that replacing the oil seal plug would be the next step before removing and disassembling the engine. 

[Awful_Charlie]

Just a few thoughts, although I've no experience of this directly (and not an A&P)

Have you checked the drive into the governor by removing it and turning the engine over slowly by hand and looking in the end of the governor drive?  If there is no drive there then I'm afraid you are into a teardown, but it is a simple low cost check, and verifies the internal bits associated with getting the drive from the camshaft to the governor.

Is there anyone on your field you could do a prop/governor swap with, just to verify where the problem lies.  The price of another governor overhaul will probably cover a days A&P time.

I'm guessing the plug sounds a favourite, from the parts catalogue I have it looks like a 1 3/8" 71640.  There is a  2" STD-1211 also listed, but I'm suspecting that is for the fixed pitch application.

Good luck, let us know how you get on in due course

Ben

[Dklossner]

Ben,

Yes, before we had the prop guys look into the prop and conduct the 1462A test, we checked the governor drive - all was good.  Hopefully today, we will have the opertunity to inspect the plug one more time. 

thanks for your thoughts. 

David

 

 

 

[Dklossner]

To all,

It turned out to be a poorly installed plug in the crankshaft.  We were able to diagnose the problem by exerting a small amount of pressure in the crankcase pressure relieve port. 

[carusoam]

David,

That sounds like a great way to test for the leakage...

So, how did MooneySpace work for you?  You put in your request for help at 7:28am on January 8 and within six hours you got four responses and one included the following advice....

"[3] Oil is leaking uncontrolled inside the system.  Oil pressure enters the the shaft through holes in the side by a hose supplied by the governor.  If the plug becomes unseated, the oil pressure that is supposed to hold your prop angle of attack / rpm is now leaking back unnoticeably into the crank case.

Fortunately the fix is simple.  Remove the prop, inspect the plug and put it back ih place."

 

Were you able to use the advice?  Did this save you any time, money or heartache? - The power of MooneySpace....

I am glad you were able to post the resolution.

Best regards,

-a-

[takair]

Quote: Dklossner

To all,

It turned out to be a poorly installed plug in the crankshaft.  We were able to diagnose the problem by exerting a small amount of pressure in the crankcase pressure relieve port. 

[Dklossner]

Keep in mind that the Lycoming test  (propeller oil control leak test - Lycoming SI 1462A) showed insufficient pressure – actually zero PSI .  Additional, you could feel a significant amount of air pressure coming from the oil fill tube - again confirming that there was a leak.  The Lycoming engineers provide four potential causes:

1.       Engine - Front main bearing needs to be replaced – apparently there is a relationship to the front bearing and the oil supply to the governor. 

2.       A plug located on the crankcase has become lose and needs to be replaced

3.       The transfer collar needs to be rebuilt

4.       A piston which controls prop pitch has oil on both sides and needs to be rebuilt.

We had eliminated the transfer collar and the piston potential causes.  So that left the front main bearing or the plug.  The issue is you can't easily determine if the plug is leaking.  So we applied 25 PSI of air pressure (we made a small rubber adaptor to plug into the crankcase breather vent port (see page 7-19 Airplane and System Description formthe POH) and only then could we see oil/air/bubbles leaking around the plug.  We were concern to add too much pressure to the engine - so we limited the test to 25 PSI. 

Hope that helps. 

Regading Mooneyspace - it is a great tool.   I believe,  my experiance and test may help others which is one of the great benifits of Mooneyspace. 

 

[takair]

David, very helpful.  Thanks for posting the details!