Propeller RPM control issues

[Andy95W]

There's a thread around that talks about vernatherms.  210° is pretty hot at the oil temperature thermocouple.

I'd look at your vernatherm is getting old and not opening enough.  Once your oil temperature is steady at 180-190°, I'm interested to hear how your pressure looks.

[carusoam]

Vernatherm central....

https://mooneyspace.com/search/?q=Vernatherm&quick=1

People have been discussing oil temps and what to look for...

From cleaning oil coolers to getting them OH’d...
 

Using an IR thermometer can find blocked tubes...

 

The Vernatherm is an thermostat / valve for the oil cooler...  they don’t last forever... easy to test too...

Also inspect the surfaces that the vernatherm touches and seals against...

If the oil doesn’t get cooled properly It’s viscosity goes thin like water...

bad viscosity Is hard to get pumped properly... it leaks back through the pump gears too fast...

 

MS has a good prop guy if there is ant questions regarding the prop...

PP thoughts only, not a mechanic...

Best regards,

-a-

[hammdo]

That is one of my thoughts — oil cooler

a partially blocked cooler can raise temps and lower pressure. You could also check temp drop across the inlet and outlet to see if the cooler is doing its job, using the ir tool.

I’d check when it was last flow checked/cleaned/OH.

next could be wide tolerances for the pressure drop, oil pump weak. The higher temp should really not drop the psi too much if it’s a good oil and quantity is right.

-Don

 

 

[Flybeech21]

5 hours ago, hammdo said:

That is one of my thoughts — oil cooler

a partially blocked cooler can raise temps and lower pressure. You could also check temp drop across the inlet and outlet to see if the cooler is doing its job, using the ir tool.

I’d check when it was last flow checked/cleaned/OH.

next could be wide tolerances for the pressure drop, oil pump weak. The higher temp should really not drop the psi too much if it’s a good oil and quantity is right.

-Don

 

 

The previous owner apparently sent the oil cooler off to be flushed.  Thats all I know of what has happened with the oil cooler.

 

[chooch]

10 hours ago, Flybeech21 said:

  

9 hours ago, Flybeech21 said:

@Flybeech21

I'm terrified reading your posts as I've been experincing very similiar issues for couple of months now :-(((

In my '77 J 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 ran 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 and supplied compressed air the blades moved but gurgling in the engine was even louder.  

Are there still any checks I could do to make sure that engine overhaul (which I cannot afford at the moment) is the only option left for me? Is there any chance that repeating Lycoming leak test with engine and oil warmed up to normal operating temperatures will give better results?

 

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. @Flybeech21 Did you do the leak test with prop off? The Instruction 1462A says the prop should remain on the engine as otherwise there is big hole at the end of crankshaft which does not allow to create proper counterpressure to be measured by leak detector. 

I'm also running out of ideas and engine oh is not really an option for me at the time being so any hints/help wellcome.

 

 

 

 

[Flybeech21]

I did the leak down test with the prop installed.

[chooch]

13 hours ago, Flybeech21 said:

I did the leak down test with the prop installed.

Was the test done with engine and oil warmed up or at ambient temperature? What pressure did you achieve?

[Flybeech21]

On 7/12/2020 at 6:08 AM, chooch said:

Was the test done with engine and oil warmed up or at ambient temperature? What pressure did you achieve?

It as warm.  35 psi.

[carusoam]

Kevin,

Got any data from the engine monitor that can be shared?

a picture is worth 1000 words... data, is even better..!

 

Can you update a description of what is going on with the rpm?  What happens, when it happens, anything that goes with that?

PP thoughts only, not a mechanic...

Best regards,

-a-

[Bartman]

I’m sure I’m missing something here, but why does your photo look different than mine? Is that a test fitting?

 

[chooch]

5 minutes ago, Bartman said:

I’m sure I’m missing something here, but why does your photo look different than mine? Is that a test fitting?

On my picture you can see tip of air gun pushed against fitting in engine's case - I did it to test if prop blades would move when supplied with airflow higher than through the leak detector. 

Main difference is that your engine has oil cahnnel from the governor to prop made of steel or aluminium tube while in my engine this connection is done with flexible hose - both versions are mentioned in Lycoming Parts Manual (steel tube is better as it has no lifetime limitaions while hose or aluminium tubes require periodic replacement).

 

regards,

 

m.

[takair]

On 1/17/2020 at 9:43 PM, Flybeech21 said:

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

There is a thread somewhere with pictures of A Potential issue with the pickup path between the sump and accessory case.  This occurs where the gasket becomes part of the path.  Usually this issue also results in fluctuating or loss of oil pressure too.  As I recall, this was not mentioned as a symptom...or was it?

[Flybeech21]

Sorry I have been so absent on the forum.

Well folks, my problem still persisted after trying everything known to man to try and solve the issue.  I installed the restrictor plate and the problem was a little better.  After hagleing  with the engine shop for nearly a month, we decided to pull the engine, tear it down and inspect.  After a year of throwing money at this issue at the direction of the engine shop we are finally at the point where they say "lets pull it and tear it down."  

After pulling the engine, we found the problem.  The two dowel pins (see photo) in the forward main bearing area were drilled all the way trough and the pins were hollow.  The pins reside in the shaft galley for the propeller oil supply.  So, oil was being dumped back into the case at a rate determined by the viscosity of the oil.  This is the reason when oil temp increased, prop RPM increased.  

DIVCO is at fault.  DIVCO overhauled and yellow tagged this case after performing faulty workmanship.  PLAIN AND SIMPLE!!!!!!   I have poured countless hours of labor and $12000 into chasing this issue when it was DIVCO's terrible work the whole time.  At the present time they are only willing to cover the cost of reoverhauling the case and buying a new set of bearings.  The engine shop is handing communications with them for now. Once they are done "getting what they can get" then I will start my part.  They should cover a hell of a lot more than fixing the case and buying new bearings.  

I will keep you guys updated.

Sorry for the absence.  

IMG_0427.HEIC

[takair]

Wow, thanks for sharing.  Truly difficult to diagnose that one.  Wonder how that slipped through the system with them doing so many cases. Hope things work out financially.  Couldn’t open the attachment, were those images?  

[Flybeech21]

1CA48BAD-2B61-432A-AC9A-79D51E18461D.heic

[EricJ]

Here it is.

[carusoam]

Great pic Fb!

That is amazing problem solving! (Unfortunate how expensive it is...)

Thanks for sharing all the details...

Best regards,

-a-

[PT20J]

Bummer. That’s the problem with warrantees, though. They generally only cover replacing the parts but not the labor or damages. 

Skip

[cliffy]

Not trying to throw a wet blanket on your parade but you THINK you have found the problem. Only a test flight will  prove it.

My questions would be -

If those dowel pins are supposed to be solid per the IPC (the IPC was checked correct?) then what are hollow pins used for in any engine?

Where did they come from and what engine are they used in?

What is their part number vs the P/N of the solid pins?  Did you verify with the parts catalog rather than someone just making an assumption? 

I would make damn sure of the correct part numbers at this point before the engine goes back together.

How did hollow pins get in the parts supply line if they were not supposed to be used? 

Verify everything at this point before assembly. No assumptions or guessing. Ask for copies of the IPC call outs and the P/N labels of what goes in. 

Verify Verify Verify

[hammdo]

@N201MKTurbo nailed it on the 4th post. He noted front main bearing leaking...

-Don

[N201MKTurbo]

I don’t know if my dowels are are drilled through or not, but they end in a solid piece of aluminum.

[N201MKTurbo]

FWIW,

The local engine shop (Aircraft Engine Specialists), who has been very helpful in this rebuild. Told me not to send my cases to DIVCO. They said they send their cases to Nickson’s in California. So I did too. Rudy at Nickson’s said my cases were previously overhauled by DIVCO, because they had DIVCO numbers stamped on them. He said Lycoming sends all their cases to DIVCO for their factory reman’s. Rudy said DIVCO sends cases to him that they can’t (or don’t want) to repair. 
 

I will leave second hand opinions of DIVCO to the people who made them.

[N201MKTurbo]

I’m not a lawyer, but your engine shop accepted the case from DIVCO and the warranty was between them, not you. It seems like your beef is with the engine shop and their beef is with DIVCO.

[robert7467]

Mine had a similar issue. I found a dirty oil screen and the linkage to the govenor was completely loose. That fixed the issue for me!

[chooch]

42 minutes ago, robert7467 said:

Mine had a similar issue. I found a dirty oil screen and the linkage to the govenor was completely loose. That fixed the issue for me!

Lucky you. My linkage to governor was checked when governor came back from overhaul. Oil filter is clean but perhaps it's good idea to check also oil screen. BTW: anyone has an idea how to remove this screen tube? Space seems very tight and I doubt I will be able to retract the screen