Piston ring gaps - can they rotate in service?

[Katamarino]

Your thoughts would definitely be welcome.

The engine is an O-470-50. At the end of 2019 it had about 650 hours. The starter bearing adapter failed and put metal into the engine. This necessitated a bulk strip. We found that the camshaft and lifters were a little pitted; enough that we decided to replace them given that I'd be flying the aircraft over the Pacific, and the case was already apart anyway. One cylinder was also very low compression. I decided to replace all 6, as one had already been replaced previously and I suspected the remaining 4 might not be far behind.

I then flew for about 260 hours on the repaired engine in the next year. It was broken in fully in line with recommended procedure. It never sat for long, and had oil and filter changes every 25-50 hours depending on how much time I was putting on. The hottest 2 cylinders occasionally briefly touched 400f, but the majority of the time they were at 380 or below. The other 4 never got above 380.

It sat hangared in New South Wales from December 2020 until November 2021, fully inhibited in line with Continental's instructions. We then flew it 0.3 hours to the shop for annual.

Annual revealed one cylinder with 48/80 and when we pulled it we found hugely worn exhaust valve guides. We checked the other cylinders and 4/5 were the same. We also found the camshaft and lifters severely pitted. Pictures are attached.

 

[Bell206]

put metal into the engine.

Was the oil cooler, internal oil galleys, oil sumps, external oil lines, etc. flushed completely of the failure debris as part of the tear down and maintenance performed?
Did the good #6 cylinder show any signs as the other 5 did?
Is there a solid paper trail of the parts installed?
Did you get an oil analysis done at this annual? This is an important item to know the results. If it picked up debris from the start adapter failure in this sample this could be one possibility of this type widespread damage and wouldnt be the 1st time something like this has happened.

I'm not an engine expert but I find this type damage to be more mechanical in nature than heat related based on these pics and your explanation. Perhaps PM Dan Thomas and get his input?

 

[Checkout_my_Six]

Bad lifters….poor heat treat will do that.

 

[Dan Thomas]

Was the oil cooler, internal oil galleys, oil sumps, external oil lines, etc. flushed completely of the failure debris as part of the tear down and maintenance performed?
Did the good #6 cylinder show any signs as the other 5 did?
Is there a solid paper trail of the parts installed?
Did you get an oil analysis done at this annual? This is an important item to know the results. If it picked up debris from the start adapter failure in this sample this could be one possibility of this type widespread damage and wouldnt be the 1st time something like this has happened.

I'm not an engine expert but I find this type damage to be more mechanical in nature than heat related based on these pics and your explanation. Perhaps PM Dan Thomas and get his input?

Badly worn valve guides. New cam and lifters worn out. What oil was used in this engine? Who made the cam and lifters?

 

[IK04]

That doesn't look like spalling, it looks like impingement. Particles of something hard in the oil might cause that, or the lifters just fell apart due to poor quality.

 

[Katamarino]

Was the oil cooler, internal oil galleys, oil sumps, external oil lines, etc. flushed completely of the failure debris as part of the tear down and maintenance performed?
Did the good #6 cylinder show any signs as the other 5 did?
Is there a solid paper trail of the parts installed?
Did you get an oil analysis done at this annual? This is an important item to know the results. If it picked up debris from the start adapter failure in this sample this could be one possibility of this type widespread damage and wouldnt be the 1st time something like this has happened.

I'm not an engine expert but I find this type damage to be more mechanical in nature than heat related based on these pics and your explanation. Perhaps PM Dan Thomas and get his input?

A new oil cooler was also installed (old one had a leak) and I'm told a thorough flush of everything else was carried out.

Cylinder 6 shows no issues, and is from an entirely different serial number range from the other 5 which are sequential. Suggests a bad batch to me.

Yes, there's a solid paper trail of the parts.

No oil analysis; I was having it done religiously prior to the first bulk strip, but it showed absolutely nothing so I stopped seeing the value.

 

[Katamarino]

Badly worn valve guides. New cam and lifters worn out. What oil was used in this engine? Who made the cam and lifters?

It has been run on Aeroshell 100 for the break in, and then Aeroshell W100 or W100+. The parts are all from Superior.

 

[Bell206]

A new oil cooler was also installed (old one had a leak) and I'm told a thorough flush of everything else was carried out.

I'd have them detail what oil flush process they used. A lot of material can remain in the oil galleys, etc. which a quickie douche with varsol wont catch. Unfortunately it does not take a lot of high carbon steel debris to do damage in a short period of time. Is Superior requesting any of these parts back for analysis or warranty?

I was having it done religiously prior to the first bulk strip, but it showed absolutely nothing so I stopped seeing the value.

FYI: there"s always value in more information. I always recommend oil analysis as it can look into the future in some cases.

 

[Dan Thomas]

It has been run on Aeroshell 100 for the break in, and then Aeroshell W100 or W100+. The parts are all from Superior.

OK. Oil should be good. The other thing I note is the damage across the entire face of the lifter, implying possible corrosion. Was this engine ground-run and put back in the hangar regularly instead of flying it?

That still doesn't explain worn valve guides, though. Lyc had a problem with their guides up until 1999 when they went to a high-chrome-content bronze guide. The other guide wear factor is a sideways push on the valve stem by the rocker. Wrong rockers?? Unlikely, but aviation maintenance is full of surprises...

 

[Katamarino]

OK. Oil should be good. The other thing I note is the damage across the entire face of the lifter, implying possible corrosion. Was this engine ground-run and put back in the hangar regularly instead of flying it?

It was not. On the only occasion that it sat for a long time, it was inhibited in line with Continental's published procedures. When it sat for shorter periods (weeks) it was always with freshly changed oil, in a hangar, and not ground run. Superior will take all the parts back to look at for warranty. Luckily I can't fly now anyway due to aircraft being in a different country to me!