Mystery of short cylinder life discovered on Acclaim?

[PMcClure]

Spent the day at TCM in Fairhope. I recommend this to anyone, I learned a lot about my engine and operations and just liked the people there. Anyway, I was talking with Rodger Gradle and Bill Ross about cylinder life on the 550's. Roger stated that they have discovered that the oil separator installed on the Acclaim is causing high crankcase pressures (3 times their spec). A fix is in the works that will require a new oil separator and change to the exhaust pipe. Some details to work out but TCM and Mooney are discussing exactly how this will be communicated to customers. 

 

The Ovation (no turbo) does not have the air oil separator. I had my crankcase pressure checked and it was nil. I also had them check the fuel pressures and flow and found that my ship flow meter was off and the flow had been set to this ship meter in the past. Actual pressure (and flow) was lower than reading. TCM recommends this calibration be done every year. 

[philiplane]

Fuel flow is always set by reference to calibrated gauges, and never to the ship fuel flow meter. Unfortunately, most shops don't have the correct gauges so they go by the ship fuel flow meter.

 

Acclaims suffering from short cylinder life are probably run by the book, which allows 85 percent power cruise settings. Any engine will have short cylinder life at those settings.  

[Lood]

Aren't airplane engines certified to run at their rated power for the duration of the TBO? Or supposed to...

[Joe Zuffoletto]

A fix is in the works that will require a new oil separator and change to the exhaust pipe. Some details to work out but TCM and Mooney are discussing exactly how this will be communicated to customers.

I had this modification made to my Acclaim shortly after I bought it in 2011, and it indeed fixed the problem. During my last annual my cylinders checked out A-OK and I should never need the premature top overhaul that some suffered.

[PMcClure]

I discussed cylinder life at length with both Roger and Bill. The cylinders are certified to last to TBO at "max recommended %" rated power or below. I was there for an honest evaluation of my cylinders as I reach 1300 hours. I am still in tolerance, about where you would expect. The oil separator issue in the Acclaim is installed by Mooney, not TCM and increases the crankcase pressure up to 12 psi and worse as it ages. Roger told me they found this problem when a wounded Acclaim diverted to Fairhope for oil on the windshield. This lead to finding the problem of high crankcase pressure caused by the oil separator. TCM made Mooney aware of this during their hiatus. I don't have a dog in this fight, but thought some Acclaim owners may want to know what has been found. 

 

Edited to include max recommended %.

75% for the Ovation 550G.  

[Piloto]

The problem could be related to routing or point of the oil return line of the oil separator. The oil in the oil separator container is emptied after engine shutdown by gravity when there is no crankcase pressure. If the return line is blocked or restricted oil can accumulate in the container to the point of restricting crankcase ventilation. My M20 separator discharge into the valve cover of cyl.#4 Never had any problems with it but mine has no turbo. It is important that the oil separator intake be higher than the crankcase vent port. This reduces the amount of oil vapors into the separator. The viscosity of the oil is another factor. 100W is harder to discharge than 15W-50 after engine shutdown

 

José

[mike_elliott]

Roger is the best. He mentioned this issue with the Acclaim at the last Mooney Summit. They run a first class operation in Fairhope.

[kmyfm20s]

Is it a particular brand of air/oil separator and would the same condition exist in a non turbo engine with the same seperator? How does high crank case pressure cause the cylinder life to be shortened?

[PMcClure]

They said the max recommended crank case pressure is 3psi for the 550G. I think this issue with the oil separator was both the size and the way it emptied into the exhaust. Overtime, "coke" would build up in the line and restrict the flow causing a build up in pressure. 

[PMcClure]

Here is the link for Service Bulletin for max crank case pressures. Measured in mph! Too Funny! I never learned that measurement in engineering school. 4 inches of H2O= 90mph!!

 

M89-9    

[kmyfm20s]

I understand how it can increase crank case pressure what I don't understand how increased crank case pressure effects cylinder life. Does it prevent oil nozzles from spraying properly, an opposite pressure on he bottom of the cylinders making them work harder, or preventing the contaminants from being removed?

[carusoam]

Inquiring minds would like to know...?

Best regards,

-a-

[Jeff_S]

This is good info...I may pay a visit to the TCM factory since it's pretty close by (especially at Ovation speeds!).  Thanks for sharing, Paul. Still no takers on 51K?

[PMcClure]

51K is still mine. Several inquiries open.   The more I fly it, the less I want to sell it! 

 

The explanation on positive crank case pressure is that the pressure below the ring disrupted the seating of the rings. Also there was some discussion about corrosive combustion gases. The bird that came into Fairhope and oil spraying out the nose seal caused by internal pressure.

 

The test was simple, I suggest anyone to do it. And a trip to TCM was not only fun but very informative. Bill or Roger seem like they are open to talk to owners on the phone about any questions you might have too.  

[philiplane]

Aren't airplane engines certified to run at their rated power for the duration of the TBO? Or supposed to...

No, they only have to pass a 150 hour endurance test at full power.

[Piloto]

Maybe the Acclaim needs a Bravo conversion like the TLS.

 

José

[jlunseth]

The initially problem we were all hearing about, was that the oil breather line (it routes through the separator) exited into the exhaust pipe, and the exhaust pipe would coke up, choking off the exit point.  Quite a few aircraft were needing cylinders or top OH's at 400 hours.  Is this a new and different issue that the OP is talking about, or same issue.

[PMcClure]

The initially problem we were all hearing about, was that the oil breather line (it routes through the separator) exited into the exhaust pipe, and the exhaust pipe would coke up, choking off the exit point.  Quite a few aircraft were needing cylinders or top OH's at 400 hours.  Is this a new and different issue that the OP is talking about, or same issue.

Sounds like the same issue to me. But it is the first time I heard it. 

[kmyfm20s]

I had this modification made to my Acclaim shortly after I bought it in 2011, and it indeed fixed the problem. During my last annual my cylinders checked out A-OK and I should never need the premature top overhaul that some suffered.

Just curious, how many hours on yours cylinders?

[Joe Zuffoletto]

Just curious, how many hours on yours cylinders?

450.