Does anybody have the Test Plate referenced in Lycoming Service Instruction 1462A?

[Ratherbflying]

Greetings all... On my last flight I experienced a prop overspeed and an inability to hold an RPM setting in cruise. This points to a sluggish oil pressure building in the prop. We pulled the prop and checked it visually, we pulled the prop governor and checked everything on the engine side of the governor, and then sent the governor out for an inspection, reseal and test. The prop shop said that the inspection didn't reveal any obvious flaws, they hope that the reseal will solve the problem I'm having.

While I'm waiting for the governor to come back I'm considering doing the 1462A service instruction for leak testing propeller oil control (the plumbing from the governor to and including the prop.) The problem is that I have not found an economical source for the test plate the service requires; the only source I have found is Aircraft Spruce and they want $2700 for it.

So I'm thinking of ordering two, you know, so in case I lose one.

Does anyone on the Space happen to have one of these lying around the shop?

[carusoam]

If you are experiencing max rpm, including exceeding red line....

This doesn't happen very often.  I am the lucky guy that gets these kind of experiences...

Expect that the internal shaft seal has fallen out.  It is an aluminum disc that is hammered into the shaft.  It blocks the prop's oil pressure from escaping back to the sump.

for the oil pressure plate that I believe you are asking about.  EAA had detailed how to make one. My EAA friend had pointed me in that direction when my prop went on hiatus....

From my M20C experience...  My prop control stopped working one day.  The gov was very worn and got OH'd... Still had the problem. The gov is a two part fix.  It has a Gear pump,  a fly-weight controlled oilP control valve, and hoses.  (Hoses when they leak are external)

the solution was remove the prop, inspect the 50 cent aluminum disc find it amiss.  Get new disc and install it...

The crank shaft is drilled all the way through.  The disc blocks the back side of the oil pressure chamber.

If I recall correctly, there is enough logic to go through that building the pressure plate is not very helpful in the end.  You get to the point that if isn't this, it must be that...  Proving 'that' or just take off the prop and fix the seal makes more sense...

One question, while you had the prop off, did somebody check that disc?

Hope that helps.

Best regards,

-a-

[Ratherbflying]

47 minutes ago, carusoam said:

 

One question, while you had the prop off, did somebody check that disc?

 

That was the point of removing the prop before we took off the governor. Checked.

[carusoam]

Reviewing the possibilities of what causes no pressure to build in front of the prop...

1) gov gear pump not generating oil pressure.  (What drives the gear pump gears?)

2) gov control valve not holding back pressure.  Flyweight wear or valve seat dirty or wear...

3) gov oil finding a way to leak out of the system.  Internal shaft seal. External hose connections.

 

Then there is the prop itself.

4) prop not being able to react to the pressure and a big spring holding the blades flat.

 

I think I remember the mechanic using air pressure to demonstrate the blades being moved..(?)

visual inspection of the seal can reveal it being grossly out of place like mine was.  Air pressure being applied to the front opening of the shaft can reveal if air can be forced through the seal.  This would show a leaky seal that looks like it's in place.

Since I'm only a PP and not a mechanic, these were ideas I shared with my mechanic.  My observations can be in error.

What I found surprising was the mechanical blade stops did not keep the prop from over speeding. Thought there was a better setting, or my stops weren't set properly (most likely).

fortunately, the issue was fully identifiable without having to go flying.  My failure happened on the ground at my home drome.

Best regards,

-a-

[Ratherbflying]

Yeah, this one was weird the way it came up. The first flight of the day was flawless, I flew for about 45 minutes and landed for a pit stop. Twenty minutes later I climb back in and taxi out. Just as I break ground, the EDM900 warning light starts flashing and when I glance over the tach is at 2830. I still had full authority with the prop control and was able to bring it back to 2650.

In cruise I set it for 2300 but five minutes later the EDM flashed again and the tach had fallen in to the prohibited range. I twisted and it went right back to 2300. I kept a close eye on it after that. Over the airport I went full rich and pushed the prop all the way forward. It went right back up to 2830. 

So I think the oil pressure is slow to build in the prop. When I set it for 2300, I think the pressure continued to build and increased the pitch slightly. So I'm thinking there may be an obstruction between the governor and the prop.

 

[Guest]

From the drawing in the SI, it should be quite easy to build.  I'd do it for 2000$ shipped to you.

Clarence

[carusoam]

That does sound like gov not working.  The fly weights are in charge of moving the valve.  If the fly weights are inhibited, it will try to open the valve. The fact that you can adjust it, at least briefly indicates the shaft seal is still in there working.  That seal gets hammered in place.  If it escapes it doesn't have much of a chance of hammering itself back in...

the fly-weights can wear in their tracks.  The have specs for their limitations.

use caution with the overspeed.  There are limitations and inspections if it goes too much for too long.  The engine manufacturer has published details on overspeeding...

Best regards,

-a-

[N601RX]

I believe 2830 is the rpm you will get with the prop sitting on the stop before the gov supplies enough oil pressure to move it off the stop.  The tool in the service bulletin can be made very easily with basic tools.  Print a drawing of it on a 1:1 scale and the use a little contact spray to attach the paper to the piece of aluminum.  Then just drill through the holes on the paper and tap the ones that need tapping. Saw out the outline on the paper and remove the paper and your done.  

It's possible lead sludge has built up in the dome and is causing the prop to stick.  How bad was the gray sludge in the hollow nose of the crank?

[Ratherbflying]

7 hours ago, N601RX said:

It's possible lead sludge has built up in the dome and is causing the prop to stick.  How bad was the gray sludge in the hollow nose of the crank?

It was clean as a whistle, no sludge at all. The prop went out for a reseal just last year.

[chooch]

Seems like an old post but similar issue just happened to my '77 M20J - overspeed when oil is hot and no response to rpm control lever while in flight. Everything works perfect when on the ground. Just had gov overhauled but the problem still exists - during test flight after gov OH I made 2 circuit patterns with no issue but in 3rd pattern I lost rpm control again and had to reduce rpms using throttle level going with MP below 15 inHg to stay below 2700rpm. Immediately after landing I made check on the ground with full power set and everything went back to normal - proper response to rpm lever movements. No oil leakages nor starvation.

Any hints where to look for the cause?

[chooch]

On 3/25/2016 at 3:54 PM, carusoam said:

If you are experiencing max rpm, including exceeding red line....

This doesn't happen very often.  I am the lucky guy that gets these kind of experiences...

Expect that the internal shaft seal has fallen out.  It is an aluminum disc that is hammered into the shaft.  It blocks the prop's oil pressure from escaping back to the sump.

 

@carusoam

Could you elaborate a bit more on this internal shaft seal? Where is it located and how to check if it's ok or not? 

[carusoam]

1 hour ago, chooch said:

@carusoam

Could you elaborate a bit more on this internal shaft seal? Where is it located and how to check if it's ok or not? 

Imagine for a moment....

1) the crank shaft is not solid near the prop...

2) It is drilled all the way through with a large hole...

3) This hole is a chamber for oil and its pressure to be supplied to the prop...

4) This oil pressure is supplied by the governor’s gear pump...

5) Since the hole is open at both ends... the prop seals off the front end...

6) Something has to seal off the back end...

7) Call that seal... the internal shaft seal....

8) it is only accessible from the front of the engine...

9) to inspect or see what it is doing requires removing the prop....

10) A method to know if it is there... or not... put some pressure into the supply line side of the prop...

11) if the seal is no longer in place... no pressure will build... air will try to escape from the case vent...

Check with your mechanic / prop guy for proper detail...

It doesn’t take any pressure to know if the seal is not in place... you’re not trying to test the prop’s actuation this way...

 

Wait a minute....

The system works, then doesn’t work, then works again?

The gov has been OH’d...

That’s a tough spot to be in....
 

That would require either the shaft seal to physically be extra flaky.... (Possible)

Or the OH to have a bad valve seat... (more likely, since it hasn’t been proven to be working yet...)

Testing the gov... is probably less work than removing the prop...

Ask some questions to the people that did the gov OH...

Realistically there are a few parts of the gov that could be not working.... from the fly weights not moving to the control valve not closing, to its gear pump not generating oil pressure...

PP thoughts only, not a mechanic...

Best regards,

-a-

[chooch]

2 hours ago, carusoam said:

(...)

That would require either the shaft seal to physically be extra flaky.... (Possible)

Or the OH to have a bad valve seat... (more likely, since it hasn’t been proven to be working yet...)

Testing the gov... is probably less work than removing the prop...

Ask some questions to the people that did the gov OH...

Realistically there are a few parts of the gov that could be not working.... from the fly weights not moving to the control valve not closing, to its gear pump not generating oil pressure...

(...)

Thanks for detailed explanation. I already spoke with the guys who overhauled the governor - they confirmed that it was tested after OH, before shipment back to me and all worked fine. So next step is to look somewhere else - engine or prop hub.... My plan is to start with pressure test as described in Lycoming SI before I decide to remove the prop....

[N201MKTurbo]

The hollow shaft in the front of the crankshaft tends to collect sludge. It could be so full of sludge that the oil pressure is blocked. This sludge can also build up in the prop piston. You might want to pull the prop and clean it out. 

[chooch]

1 minute ago, N201MKTurbo said:

The hollow shaft in the front of the crankshaft tends to collect sludge. It could be so full of sludge that the oil pressure is blocked. This sludge can also build up in the prop piston. You might want to pull the prop and clean it out. 

I'm planning to do that if results of test described in Lycoming Service Instruction 1462A are OK. Although I doubt if there will be any blockage by sludge since with cold/viscous oil and on the ground all works fine and problem occurs only once oil gets warm and only in flight....

[N201MKTurbo]

1 hour ago, chooch said:

I'm planning to do that if results of test described in Lycoming Service Instruction 1462A are OK. Although I doubt if there will be any blockage by sludge since with cold/viscous oil and on the ground all works fine and problem occurs only once oil gets warm and only in flight....

I'm with you, just grasping at straws....

[EricJ]

BTW, my governor is currently off for overhaul, and while it is off I was looking at this SI.   My IA had already suggested blowing some air through the high-pressure oil line just to make sure there's nothing in it (which I will do), but the SI is also interesting.   Apparently the plate isn't strictly necessary since a rubber-tipped air fitting can be pressed against the propeller oil inlet on the governor pad and accomplish the same thing.   I intend to try to this and do the differential pressure test as well the same way.    As long as the governor is already off, it seems like a reasonable thing to do.   There's an AvWeb article (reprint from Light Plane Maintenance) on doing this:

https://www.avweb.com/ownership/propeller-governor-diagnostics/

 

 

[chooch]

15 hours ago, EricJ said:

BTW, my governor is currently off for overhaul, and while it is off I was looking at this SI.   My IA had already suggested blowing some air through the high-pressure oil line just to make sure there's nothing in it (which I will do), but the SI is also interesting.   Apparently the plate isn't strictly necessary since a rubber-tipped air fitting can be pressed against the propeller oil inlet on the governor pad and accomplish the same thing.   I intend to try to this and do the differential pressure test as well the same way.    As long as the governor is already off, it seems like a reasonable thing to do.   There's an AvWeb article (reprint from Light Plane Maintenance) on doing this:

https://www.avweb.com/ownership/propeller-governor-diagnostics/

 

 

Hi @EricJ. Thanks for sharing your thoughts and the link - interesting reading. Are you experiencing any issues with rpm control or just want to do the pressure test as you have the governor removed anyway? 

[EricJ]

7 hours ago, chooch said:

Hi @EricJ. Thanks for sharing your thoughts and the link - interesting reading. Are you experiencing any issues with rpm control or just want to do the pressure test as you have the governor removed anyway? 

My prop got lazy over just two flights, and wouldn't cycle unless the control was pulled all the way back.   My IA indicated that we should send the governor in, so I did that, but also suggested we should check for crap in the pressure line.  As long as we're going to blow the line out, anyway, I thought we might try the full test to make sure there aren't any other issues.

 

[EricJ]

So I got a new governor and yesterday went to blow out the high-pressure line and try the differential pressure test trick using the hint from AvWeb to just use a rubber-tipped air fitting.   It worked well enough to blow any crap out of the line (which I had disconnected at the front of the engine case), but because of the way the groove is machined in the pad in the accessory case on my engine I couldn't get a good enough seal there to do a differential pressure test.   My IA said he's been going to build one of the adapter plates to do this at home but hasn't ever gotten around to finishing it.   With the plate it would not be difficult to do.   If this ever comes up again I may fabricate a plate and try it.

So I've abandoned the effort to try the differential pressure test.   Since my prop only has about 400 hours on it it is apparently unlikely that the seal at the piston is an issue, so we'll put the gov back on this week and hope that works.   Was worth a shot, anyway, and I thought I'd report back on the results.   

[carusoam]

Thanks for sharing that tidbit, Eric!
 

I’m surprised that Lycoming doesn’t have this as a stock part...

Or maybe they do?

Best regards,

-a-

[chooch]

Thanks for update @EricJ. Hope that everything will go well with overhauled governor. I'm having the test plate machined this week (any workshop can do it - it costs $50 in Poland, most of it being price of 1/8" NPT taps not so common in Europe). If everything goes as planned the pressure test is scheduled next week.

regards,

Marek

[chooch]

Comming back on my issues with rpm control in my '77 J:

background: on the ground and with cold oil all seems to work fine, propeller responds to movements of blue lever but once in the air and oil gets warm I lose rpm control and engine overspeeds beyond 2700rpm with no response to blue lever movements (fortunately I spotted the issue on time and immediately reduced thrrotle to stay below 2700rpm).

I got governor overhauled but problem still not solved.

Yesterday I performed leak down test according to Lycoming SI 1462A but with engine and oil at ambient temperature (no engine run up prior to the test) - with 40 psi on Gauge #1 of the leak detector there was only 1-2 psi on Gauge #2 and I could hear clear gurgling inside the engine. Prop blades didn't move so I twisted them back and forth couple of times together with turning the prop - all I managed to achieve at some point was short (30 second) indication of 20 psi on Gauge #2 but it happend only once and for short time - afterwards pressure on second gauge stayed just slightly above 0. 

I also checked passage though prop control oil hose (from governor prop control port to front engine port) and there is no blockage in it. Also when I pushed air gun to engine front port (see one of attached photos) and supplied compressed air the blades moved but gurgling in the engine was even louder.  

So, before moving to next step i.e.  pulling the propeller off, couple of questions:

1. Is there any chance that repeating Lycoming leak test but this time with engine and oil warmed up to normal operating temperatures will give better results?

2. @carusoam: If it turns out that the aluminium disc in the crankshaft is leaky or gone, is it something what can be fixed in the field, without dismantling the engine? My Lycoming guys told me that this requires the crankshaft to be sent to Lycoming for this fix and quoted it for over 13.000 USD.... :-( BTW: it's item #7 on attached drawing from Lycoming parts manual,. right?

thanks in advance for any hints or help,

 

regards,

Marek

 

[carusoam]

Marek,

The shaft seal is a round aluminum disk, accessible when the prop is removed...  (looks like #3 above, when placed in the hole it looks like #7)

Sounds like it may be leaking... more as oil warms up... When it leaks more than the gov’s pump can supply, you get a runaway rpm... a related rates problem...

If your governor is working... It’s gear pump pushes oil towards the prop... the gov’s oil control valve builds the pressure in the prop as it closes...

The oil pushed into the prop by the gov, drains back to the sump when it passes out the control valve...
 

When my M20C ran into this challenge... we OH’d the gov, because it needed it.... I don’t recall how we tested the prop...  after that, we pulled the prop to see the 50cent aluminum disk got dislodged...

Pulling the prop is a small pia... lots of nuts, small even turns, to make progress... and safety wiring...

When using air, make sure it isn’t leaking back through the gov... that will make sounds in the engine sump as well...

Review how the prop is plumbed... two(?) oil hoses, supply and return..? (I have forgotten over time...)
 

There is probably a right way to remove the old seal... sending it to Lycoming and spending 13 AMUs.... wouldn't be my choice... a hammer and brass rod probably got used to mangle the seal and make removal easy...
 

Clean and inspect to make sure the next seal will go in place properly...

I had an excellent working relationship with a really good mechanic...   

Normal failure for this seal... it gets out of place slowly... and leaks a little... then it becomes dislodged and leaks a lot... it never goes back in place on its own...

PP thoughts only, not a mechanic...

Best regards,

-a-

[V. Das]

We had one case where the Propeller Governor is not able to bring the RPM below 1590 rpm with prop lever at low rpm position.

Changing the governor did not help. Plan to do the leak down test according to Lycoming SI 1462A.

I am not sure if there is a schematic that will help to illustrate the failure of the system to hold the pressure