Propeller RPM control issues

[Flybeech21]

I am having prop RPM control issues.  The power setting for today's short, low-altitude flight was 25"/2500 RPM.  On today's flight, during descent, the prop RPM started increasing.  In response, I pulled the prop control to reduce the RPM with no success.  I pulled the prop control to min gov and it had no impact.  If I increased the throttle anywhere above 17" MP, the RPM would increase to over 2700 RPM.  Luckily, this was on descent to the airport.  After landing, I did a run up check and prop cycle - no prop RPM change.  I shut down and restarted and then repeated the run up check and it operated perfectly.  

So, I decided to take the plane up for a test flight.  Everything worked perfectly until: I pitched the airplane down and noticed a slight RPM increase.  I pitched the airplane up to maybe 2.5 Gs and the RPM stabilized back to normal.  Then, I pitched the nose forward to around a 0 - 0.5 G load and the RPM instantly surged to above 2700 RPM.  When I pitched back to positive Gs the RPMs stabilized and functioned normally.  WTH?

Oil pressure during the event was at the bottom of the green arc.  When on the ground at idle the oil pressure was at the middle of the green arc.  

More History.  The previous owner had RPM problems.  He traded props with a fellow 20E owner and replaced the prop governor with a new one.  He says the problem never repeated after that.  This was approximately 5 hours prior to me purchasing the airplane.

The engine was recently O/H by a reputable engine shop.  It is at <70 TSMOH.

Well, its back.  And, I am really scratching my head here on what the problem could be.  Maybe the new governor is bad?  Maybe there is a problem with the plug in the crank?  I am really flummoxed.  

BTW, this is the Hartzell HC-C2YK-1BF propeller subject to the 100-HR AD.

Any suggestions?

[EricJ]

RPM increasing means the prop isn't getting sufficient oil pressure.   If your in-flight oil pressure is low, it may not be the governor.   If it is pitch/g dependent, it could be your oil level is low or your oil pump isn't picking up for some reason.    With such low time on everything it could be something wasn't put back together correctly.

First thing I'd do is check the crankcase oil level just to be sure.

Edited January 18, 2020 by EricJ

[Flybeech21]

3 minutes ago, EricJ said:

RPM increasing means the prop isn't getting sufficient oil pressure.   If your in-flight oil pressure is low, it may not be the governor.   If it is pitch/g dependent, it could be your oil level is low or your oil pump isn't picking up for some reason.    With such low time on everything it could be something wasn't put back together correctly.

First thing I'd do is check the crankcase oil level just to be sure.

The oil level is normal.  Maybe the pickup is faulty in the sump?

[N201MKTurbo]

Maybe a leaking front main bearing.

Or your crank is full of crud.

[Flybeech21]

6 minutes ago, N201MKTurbo said:

Maybe a leaking front main bearing.

Or your crank is full of crud.

I thought of the crud too.  But this thing is brand new.  The engine shop is very reputable and doesn't cut corners.  

I would really like to find an option other than: pull the engine and re-overhaul it.

[N201MKTurbo]

Just now, Flybeech21 said:

I thought of the crud too.  But this thing is brand new.  The engine shop is very reputable and doesn't cut corners.  

I would really like to find an option other than: pull the engine and re-overhaul it.

Maybe the governor is sucking air.

[Flybeech21]

Just now, N201MKTurbo said:

Maybe the governor is sucking air.

This is a possibility.  It is an external oil line subject to an AD.  There was some quibbling between the engine installer and engine shop over who was responsible for that AD.

Ill check it tomorrow and let you know what I see.

[chriscalandro]

What prop governor is it?

[takair]

The line would be the pressure side, but the gasket or mounting face of the governor or case may have a flaw and draw air.  I’ve also seen the sump/accessory gasket bad and allowing the oil pump to draw air....that one may actually be sensitive to aircraft pitch.  You mentioned pressure indication was toward yellow, is this only when pitched down?

[Flybeech21]

I am going to fly it tomorrow and note these areas.  I will pay attention to oil pressure relative to g loading.  Also, I am going to look at oil pressure relative to sustained pitch attitude.

Any thing else?

BTW, thanks so much for giving me advice here.  I have to figure this out.

Kevin

[takair]

4 minutes ago, Flybeech21 said:

I am going to fly it tomorrow and note these areas.  I will pay attention to oil pressure relative to g loading.  Also, I am going to look at oil pressure relative to sustained pitch attitude.

Any thing else?

BTW, thanks so much for giving me advice here.  I have to figure this out.

Kevin

Might as well watch oil temp in relationship to pressure.  Usually is inverse...but my guess is it won’t be in this case.  If you have cowl off, look for oil leaks off the governor.  It sometimes puddles in the cove in the firewall before working it’s way down.

[tmo]

At a risk of sounding stoopid, it isn't the linkeage between the cockpit prop control and the governor, right?  It could fail in / to a forward position?

[carusoam]

I’m the voice at the back of you head? 

 

The governor system is proven to not be working properly... could be a simple oil leak.

Fly it... risk overspeed of the engine... manually watch/control rpm, full power can’t be available...

This goes in the do not fly box until the problem is known...

 

In the shop... it is easy to pressurize the system to know where the leak is occurring...

 

To continue to fly it and hope the engine tells you what is wrong is relying on hope...

Hope makes a crummy flight plan...

 

So...

Where does this rant come from..?   My M20C lost the disc seal at the back of the shaft.. it leaks oil pressure into the case...

To produce enough power for continued flight it is in or near the overspeed range...

or while flying the plane the rpms climb well past the governed range...

The prop would have to be set-up with impossible precision to have the stops be in the right place for 2700 rpm... it just doesn’t work that way...

You might consult with out prop guy to better understand what you want to do...  @Cody Stallings

Call me a friend, looking after the health of your engine...

PP thoughts only, not a mechanic...

Best regards,

-a-

 

[takair]

Anthony makes some good points above.  I mentioned a previous experience where the engine was sucking air.  Admittedly, that was on a 540.  Attached is the image of the location on a 360 that can cause a similar issue.  In your situation, because it is only doing it pitched down, it may be that the oil in the sump prevents cavitation until it is not over the void.  That leads me to believe it may be on the inside of this area.  In the situation I mentioned, the oil pressure would drop at high power, where the pump was working harder and it would suck the cut gasket in (as I recall, someone damaged it removing the accessory section and tried to use RTV to seal it rather than dropping the sump to replace it). 
 

I hope you are able to sort this out.  I would start by looking for leaks....governor and in the area shown.  Then perhaps pull the governor to see if the gasket and machined surface is in good shape.  There is also a test to check the crank and prop oil path...it is a pressure test.  A little more involved and I can’t quite correlate it to pitch attitude.  Be sure the suction screen crush washer  is not leaking or missing.  Last is the sump/accessory case gasket I mentioned.  Not the easiest to change on a Mooney.

[Flybeech21]

11 hours ago, takair said:

The line would be the pressure side, but the gasket or mounting face of the governor or case may have a flaw and draw air.  I’ve also seen the sump/accessory gasket bad and allowing the oil pump to draw air....that one may actually be sensitive to aircraft pitch.  You mentioned pressure indication was toward yellow, is this only when pitched down?

Thanks a ton Takair.  I am heading down to the hanger now.  I'll let you know how it works out.

I spend a lot of time in the hanger these days.  I am having to do a top overhaul on my Pitts since I burned the jugs up at Reno last year.  ughhh..

[drapo]

I had a similar issue after I got my engine back from the overhaul shop. Although I did not get quite a dramatic surge in RPM, but a sluggish prop control, low oil pressure and  an oil leakage at the governor. Sent the governor to the prop shop, thinking overhaul, but it passed the leak test and the technician ended up only changing the bearing since the governor was already off.

When I picked up the governor, the shop owner shared this Lycoming bulletin and told me that my problem could be that the gaskets didn't do their job and this could resolve the issue: https://www.lycoming.com/sites/default/files/Propeller Governor Pad Plate PN LW-12347.pdf

We did order the Lycoming pad plate, about a $100 part and installed it and the leakage stopped along with all other symptoms. Not saying that this is your solution, but could be worth a try!

[takair]

9 minutes ago, drapo said:

I had a similar issue after I got my engine back from the overhaul shop. Although I did not get quite a dramatic surge in RPM, but a sluggish prop control, low oil pressure and  an oil leakage at the governor. Sent the governor to the prop shop, thinking overhaul, but it passed the leak test and the technician ended up only changing the bearing since the governor was already off.

When I picked up the governor, the shop owner shared this Lycoming bulletin and told me that my problem could be that the gaskets didn't do their job and this could resolve the issue: https://www.lycoming.com/sites/default/files/Propeller Governor Pad Plate PN LW-12347.pdf

We did order the Lycoming pad plate, about a $100 part and installed it and the leakage stopped along with all other symptoms. Not saying that this is your solution, but could be worth a try!

That is interesting.  I wonder why the plate would help?   Perhaps there is some known deformation that occurs and the plate allows for doubling the gasket to take it up?

[Flybeech21]

OK.  Problem solved.  I went to the Hartzell maintenance manual 115N.  Ran the applicable trouble shooting procedure and discovered that there was no grease in the prop.  I greased it IAW the instructions and flew it and it worked perfectly.  

Now to give the previous owner's mechanic a call...

 

[chriscalandro]

Oof. 

[carusoam]

Great follow-up Kevin!

Anything is possible...

Best regards,

-a-

[Cody Stallings]

9 hours ago, Flybeech21 said:

OK.  Problem solved.  I went to the Hartzell maintenance manual 115N.  Ran the applicable trouble shooting procedure and discovered that there was no grease in the prop.  I greased it IAW the instructions and flew it and it worked perfectly.  

Now to give the previous owner's mechanic a call...

 

Negative. 
Need to pay close attention to the Prop Gov in this situation. 
Putting grease in the propeller doesn’t have anything to do with it not maintaining RPM.

The Grease just Lubricates the Thrust Bearings.

Bout 18/19in is where my F model gov would go off line. At that point the prop will be pushing the engine. If you push the power to 20/22in( somewhere in that area) you should get a very noticeable rpm reduction an be able to hear the Gov load the propeller with pitch.

I would be very curious to know if you have a Hartzell H-1 Gov.

This same thing happened to me. Propeller control full out would only pull it down to 2550 Rpms. 
Turns out the Gov was internally bypassing the oil that was needed at the prop.

Keep a close eye on this issue. “Down shifting” to Granny Low isn’t a good idea at 140Knts

[chooch]

On 1/18/2020 at 8:18 PM, Flybeech21 said:

OK.  Problem solved.  I went to the Hartzell maintenance manual 115N.  Ran the applicable trouble shooting procedure and discovered that there was no grease in the prop.  I greased it IAW the instructions and flew it and it worked perfectly.  

Now to give the previous owner's mechanic a call...

 

Has this been really solved by greasing? I'm expecting overspeed issues and lack of rpm control in flight, when oil gets warm (on the ground everything works fine). Governor was overhauled and installed IAW M20-120 Service Instruction but problem did not disappear  I have 3-blade Hoffmann prop and there is nothing mentioned in the maintenance manual but perhaps your solution could be also applied here.... Which page of 115N manual described the procedure you applied?   

Edited June 17, 2020 by chooch

[Flybeech21]

Well Damn.  My problem is still not solved.  I have been off of the thread for a long time.  But, I have been fighting this issue ever since and it is still not solved.   

Summary:

When the issue returned, I pulled the prop and sent it to the prop shop.  It was garbage.  Bad blades, bad fork, hadn't been overhauled in decades.  I overhauled it to the tune of $6000 and still didn't get rid of the 100 HR AD.  Problem solved right?  WRONG.

On the first flight after prop overhaul, the problem persisted.  I was so pissed off that I started installing the Graphic Engine Monitor that I had purchased and figured some eureka moment would happen while I was installing the GEM.  On the ground run, I noticed the factory oil pressure gauge was 15- 20 psi less than what the GEM was indicating.  After verification, the factory gauge was inaccurate.  Problem solved right???    WRONG!  I adjusted the oil pressure up to the 80 psi I though I was getting before.  I flew it again and then noticed that when the prop gov was in the operating range, the oil pressure plummets to slightly less than 60 psi ( in the yellow arc) and the problem still persisted.

I then pulled the prop off and performed the transfer bearing leak down test per Lycoming's service instructions.  No defects.  The plug in the crank was intact and the test was normal.  

I then changed the spring and ball with a stiffer spring and a new ball to get up to 90 - 95 psi.  I flew it again.  This flight I noticed that the oil pressure would steadily decline with the increase in oil temperature and would go below the magical 60 psi at precisely 210 degrees of oil pressure.  when I leveled off and kept the throttle low to prevent the persistent overspeed tendency and to allow the oil to cool the propeller system would function completely normal once the temp reduced to below 210 degrees.  Partial victory I guess.  

So this engine is still in it's break in phase.  I decided to keep flying it to continue the break in.  It operated fine as long as you kept the power back for the first 10 mins of cruise and let the oil temp cool to less than 210 degrees then operated normally.  Then I changed over to phillips 20W-50.  The issue was back with a vengeance now and twice as persistent.  

I then decided it was time to send the prop governor in.  

Aside: This was the second prop governor that was installed on the airplane chasing this issue.  After speaking with the previous owner's mechanic, he told me that they had the same squawk and fixed it with a new PCU5000 prop governor.  They flew it twice with no issues and put it up for sale.  I was the lucky buyer!!!  I asked them about the profile of the test flights and they told me that it was pattern altitude type short flights.  That is why it didn't show back up.  They never got the oil temp above 210.

The prop shop said there was nothing wrong with the governor except it was not set per the manual.  They reset everything per the manual and sent it back to me.  I reinstalled it and - you guessed it - still not fixed!

I then decided to remove the PCU5000 and go back with a Hartzell H-1.  I decided to do this after speaking with Rich (the chief inspector at PCU prop governors manufacturer).  He wanted verification that it was not some compatibility issue with the engine/prop combination that they didn't know about.  So, I did that.  It was an absolute pain in the neck.  The studs on the adapter plate were too long and had to be changed.  The Hartzell is huge compared to the PCU and required throwing a couple of wrenches across the hanger and removing the oil filter and P-Lead on the right mag to get it to fit.  It literally took me a half of a day to get the H-1 on this airplane.  

So, time to fly it again!  I flew it and the problem still persists.  I am beat down and devastated.  This flight was this afternoon.  

I am out of ideas here.  I have never had an engine issue beat me.  I have always been able to figure out what the issue is.  This one has defeated me.  I need help.

I do see some good ideas posted above.  I will forward them to the engine shop as this is now, in my opinion, an engine warranty issue.

 

Edited July 11, 2020 by Flybeech21

[EricJ]

Have you looked at the oil pressure and oil temperature traces and rpm together on the engine monitor data?    I'm still wondering if something wasn't assembled properly in the engine and you're losing pressure to the prop.  You indicated it correlates to temperature,  and viscosity is also proportional to temperature, so you may have an internal leak somewhere when it's hot, or it isn't keeping pressure up sufficiently anyway.

Since you have the engine monitor in now, it may help sort out the details of what's happening at any given moment.

 

[Flybeech21]

6 minutes ago, EricJ said:

Have you looked at the oil pressure and oil temperature traces and rpm together on the engine monitor data?    I'm still wondering if something wasn't assembled properly in the engine and you're losing pressure to the prop.  You indicated it correlates to temperature,  and viscosity is also proportional to temperature, so you may have an internal leak somewhere when it's hot, or it isn't keeping pressure up sufficiently anyway.

Since you have the engine monitor in now, it may help sort out the details of what's happening at any given moment.

 

I have been reviewing the data with the engine shop.  There is nothing to tie it to anything in particular.

I am going to mention this service instruction that installs a plate between the gov and adapter listed above.  That sounds very promising.