New governor wanders

[Dialed In]

The plane is a M20 E with a Hartzell prop. So I got my old governor changed at annual because it leaked oil and the new PCU governors were supposed to great. First flight back home run up responded well it would pull the prop down about the same as before, take off was steady at 2680, then set governor at 2500 for cruise and it would wander down to 2480 and then up to 2550-60. It was an hour flight and I tried several rpm setting all varied about the same. The old governor held rpm steady +- 10. I was wondering if anyone else saw this rpm variation right after the new install or should it be spot on right out of the box? The cable is tight with no movement in it at the clamps, oil pressure solid at 79, nothing else seems different. I was initially cruising at 10,500 with 19 in manifold but tried several power settings down low and all produced the same variation. @M20Doc are there any settings that would affect this or is it a pull off and send back in?

[carusoam]

That can’t be normal…

Of course…

The Gov may only be part of the problem…

Inside… It has an oil pump to make pressure, a valve to adjust the pressure, and fly-weights to adjust the valve….

Might want to contact the shop that installed it and ask their thoughts…

Our MS prop guy may have some experience… see if Cody is around.  @Cody Stallings

Sounds like pressure isn’t being held properly, or the prop has a control challenge…

Was there any cleaning involved in the prop’s hub, or does it still have decades of sludge getting reorganized in it?

PP thoughts only, not a mechanic…

 

Best regards,

-a-

[0TreeLemur]

Another thing to consider is the linkage between the cable and the gov.  I've noted that as the likely culprit because the rpm wanders a bit in our C. 

We installed a PCU gov. in 2019 after our original governor was found to be an antique by a local prop shop.  Looking into possible sources of wandering rpm, the linkage in our plane consists of a bolt through a heim bearing that is connected to the end of the cable, which creates an eccentric connection.   It also creates some hysteresis (slop) in the connection, especially when changing direction.    Some day I'm going to ask my A&P if he can change to more of a clevis-type connection which would eliminate that slop. 

[Guest]

8 hours ago, Dialed In said:

The plane is a M20 E with a Hartzell prop. So I got my old governor changed at annual because it leaked oil and the new PCU governors were supposed to great. First flight back home run up responded well it would pull the prop down about the same as before, take off was steady at 2680, then set governor at 2500 for cruise and it would wander down to 2480 and then up to 2550-60. It was an hour flight and I tried several rpm setting all varied about the same. The old governor held rpm steady +- 10. I was wondering if anyone else saw this rpm variation right after the new install or should it be spot on right out of the box? The cable is tight with no movement in it at the clamps, oil pressure solid at 79, nothing else seems different. I was initially cruising at 10,500 with 19 in manifold but tried several power settings down low and all produced the same variation. @M20Doc are there any settings that would affect this or is it a pull off and send back in?

Strange that a new governor would be failing from birth, but I guess it’s possible.  What type of tachometer do you have? Is it the problem?

[Dialed In]

I installed an EDM 900 this winter so the tach I believe is accurate. The prop was not pulled so it has about 10 years of buildup in it. I will check the linkage again at the governor but I did feel it before the test flight and did not notice any slack, it could have been on the stop though. It seems to be an issue in the dwell if you would call it that. The wander is slow maybe one cycle a minute.  If you nose down ever so slightly it seems the governor does not correct until it get a 50-60 rpm rise then just a slight nose up drops 20-30 under where it’s set. I’m talking slight adjustment in attitude less then 100ft/min. I am going to call the shop this morning I just didn’t want to bother them on Sunday. 

[Ragsf15e]

1 hour ago, Dialed In said:

I installed an EDM 900 this winter so the tach I believe is accurate. The prop was not pulled so it has about 10 years of buildup in it. I will check the linkage again at the governor but I did feel it before the test flight and did not notice any slack, it could have been on the stop though. It seems to be an issue in the dwell if you would call it that. The wander is slow maybe one cycle a minute.  If you nose down ever so slightly it seems the governor does not correct until it get a 50-60 rpm rise then just a slight nose up drops 20-30 under where it’s set. I’m talking slight adjustment in attitude less then 100ft/min. I am going to call the shop this morning I just didn’t want to bother them on Sunday. 

It also sounds like the curse of a good engine monitor.  You probably wouldn’t notice 20-30rpm on the analog gauge, but now you see every single rpm, amp, and psi.

[markgrue]

It is possible that there is air in the system.  A very aggressive rpm check would probably eliminate most of it.   Sometimes it just has to work itself out.  

 

Mark

[carusoam]

Interesting….

The amount of oil that goes in and out of the hub is quite small….

Would it make sense to do a few extra pulls of the blue knob during the next run-up to really exercise the system….?

 

Get an rpm app on the phone… this is an aural method of checking the rpm instrument… they work amazingly well…

PP guesses only, not a mechanic… or a mechanic guessing….

Best regards,

-a-

 

[Dialed In]

Mark you might be onto something. I talked to my A&P and he suggested I talk to the governor shop I bought it through. I called them and they said they would contact the territory service rep and he would call me. This shop has been difficult to do business with I was really hoping that the governor would work and I would never have to talk to them again but alas here I am. Anyway nobody called back, figured that would happen that’s how the entire buying process went. I think this is the last time I purchase something from a dealer outside of who my shop uses.  Anyway I have not gotten any other advice yet other then this forum but while flying it it does feel like maybe there is air in there, it is slow to react and over shoots target. If I get some time in the next couple days I’ll really pull the prop down on run up and see if that primes everything. 

[Dialed In]

Rich @N201MKTurbo any ideas?  Have you had to prime new governors?

[N201MKTurbo]

37 minutes ago, Dialed In said:

Rich @N201MKTurbo any ideas?  Have you had to prime new governors?

No, whenever I put on a new governor or a fresh prop, it is slow to respond the first few cycles then works fine.

A friend with a Comanche just got his prop and governor back from overhaul. He sent them out because the RPM was unsteady. It turned out that the pump gears were so warn that it couldn’t hold pressure. 
 

I’m no expert on governors, but I suspect the governor is the problem. Have you contacted the rebuilder and asked them about the problem?

[Dialed In]

Yes I have, it is a brand new pcu 5000 ATH-1 I’m still waiting to hear back from them. 

[carusoam]

The three parts of the Gov….

1) Fly weights… if they are sticky… they don’t fly so well… and won’t move the control valve smoothly as needed….

2) Control valve… this is the thing that sends oil to the prop or dumps it into the sump…. It needs to operate smoothly and be in good physical shape….

3) Gear pump… gear pumps simply spin and deliver oil to the system…. It is a different gear pump than the one to lubricate the engine… we don’t have an OilP gauge to show us what is happening inside the Gov….

4) introducing air into the system… Would cause some variation…. The system has a method of eliminating air as well… this one I don’t have enough memory of….   
 

See if the PCU guys have an operators manual to go with their nice Gov….?

It may give hints on what you might see….

PP thoughts only…

Best regards,

-a-