Oil control rings and lessons learned - with pics!

[PT20J]

43 minutes ago, M20Doc said:

Lycoming must have been running a sale on them.  Air Power wants more that $9000!

You really need two because the way the factory puts cylinders on is with a person on each side and they push their cylinders on at the same time and then torque them together.

[Guest]

44 minutes ago, PT20J said:

You really need two because the way the factory puts cylinders on is with a person on each side and they push their cylinders on at the same time and then torque them together.

Glad I don’t need 8 of them for my engine!

[Chessieretriever]

In my humble opinion a broken compression ring started the problem increasing blowby (and heat to the piston where these hot gases streamed by) which pressurized your crankcase and created your never ending leaks (out of every joint that was unable to handle about 5 inches of water column of crankcase pressure). Your second compression ring shows signs of carbon and temperature on the bottom half wear surface which indicates that it was not sealing either and you were hot enough to carbonize the oil that the oil control ring downstream of it accumulated until most of that oil turned into carbon and the oil ring stopped working altogether. Blowby of hot combustion gases will create very high oil temperatures which may stretch the on board oil heat rejection device beyond its capacity. I would think that any A&P that has been around these engines would look a little further if they saw a skirt that is caked with black carbon but then again maybe times have changed.

[DXB]

On 9/13/2022 at 6:48 PM, canamex said:

 

 

As an armchair A&P wannabe with no real skills, this has been a pretty educational post for me.  The question comes up - is that top ring really broken or merely sitting out of its groove after decompressing?  I had thought a broken ring would produce massive blowby - worse than the 1wt/3 hrs described here.  Asking for a friend  who is also getting the same amount of oil consumption, which is pretty stable, and wondering what to do.  

[EricJ]

10 minutes ago, DXB said:

As an armchair A&P wannabe with no real skills, this has been a pretty educational post for me.  The question comes up - is that top ring really broken or merely sitting out of its groove after decompressing?  I had thought a broken ring would produce massive blowby - worse than the 1wt/3 hrs described here.  Asking for a friend  who is also getting the same amount of oil consumption, which is pretty stable, and wondering what to do.  

The gap appears to be way too wide for where it is sitting, and there's a piece that's broken off in the groove still. 

[PT20J]

2 hours ago, EricJ said:

The gap appears to be way too wide for where it is sitting, and there's a piece that's broken off in the groove still. 

And the end of the ring doesn’t look smooth.

[A64Pilot]

3 hours ago, DXB said:

As an armchair A&P wannabe with no real skills, this has been a pretty educational post for me.  The question comes up - is that top ring really broken or merely sitting out of its groove after decompressing?  I had thought a broken ring would produce massive blowby - worse than the 1wt/3 hrs described here.  Asking for a friend  who is also getting the same amount of oil consumption, which is pretty stable, and wondering what to do.  

I’m nearly certain if it had a compression test done it would have pointed to an issue, plus I feel pretty sure the plugs would also have indicated an issue, then a bore scope would also have shown problems.

I assume no body knew to look. Surprised it wasn’t fouling plugs.

[Guest]

I pulled this piston out of an O-360A1A with almost 2000 hours on it.  It always had good compression and not horrible oil consumption.

[canamex]

11 hours ago, A64Pilot said:

I’m nearly certain if it had a compression test done it would have pointed to an issue, plus I feel pretty sure the plugs would also have indicated an issue, then a bore scope would also have shown problems.

Compression test done every annual, that cylinder always was in the high 70's. When I was AOG in Yellowknife, we pulled the spark plugs and they were decently fouled (two of them were also loose, which was troubling). Also bore scoped the cylinder and found some carbon on the inside of the wall of the #4 cylinder. In Victoria I got a stuck exhaust valve and the compression went down to 30. After fixing the valve, it went up to 60 but I was going through oil like nothing else. My best guess is that the ring broke at some point on one of the short flights in Victoria. Maybe it broke when the cylinder was pulled off. But the oil consumption became just horrendous after a few quick hop flights between Victoria and Vancouver.

[pilot_jb]

On 9/14/2022 at 9:56 PM, canamex said:

Good catch. I went back and looked at the photos and it seems that the mechanic didn't remove the piston from the cylinders and looking at one of the photos it seems as though the piston was pretty heavily covered in gunk. He didn't call it out as a concern at that time and I suppose I assumed that if it was bad then he would have mentioned something but you know what they say about happens when you ass-u-me...

So it looks like the piston/cylinder could've been hooped since way back.

I don't know your mechanic, but if he saw this and didn't realize what was going on then there is a major issue with his skill level...and there's no way he didn't see it. 

This sort of failure will usually also show up in the exhaust pipe and on the belly, as well as the plugs...even before a possible low compression reading.  

Borescope inspections are also your friend and should be conducted regularly.  I look in my cylinders during each spark plug service, and at the back of the exhaust valves (more relevant here) while the exhaust is removed at annual.  

[jetdriven]

I have a client with the 650 hour factory engine who somehow snapped an oil control ring on a flight in easy VFR conditions and nothing abnormal, and the very next flight we changed the oil and topped it off. He took off and in less than an hour it was almost completely out of oil.....were talking about a quart of oil in ten minutes through one cylinder.

[Mooney-Shiner]

On 9/26/2022 at 6:05 PM, M20Doc said:

I pulled this piston out of an O-360A1A with almost 2000 hours on it.  It always had good compression and not horrible oil consumption.

Why did your client decide to pull the cylinder at all?

[Raymond J1]

-I think that the piston best suited to the cylinder of IO 360 A1A is the PNr LW 10207.
I think so because this piston has 2 reserves on the top for the passage of the valves and this impacts the flamme front for speeds between 2400 and 2600 rpm.
This piston also has the particularity that the scraping side of the "shot" and "compression" rings is upwards, which is not the case with all pistons at Lycoming (not high compression ratio).
Finally, and this is important, the oil return holes under the oil scraper segment are larger.

-This piston has a disadvantage, the forged skirt contributes to a faster wear of the cylinder bottoms, cause of a downgrading of the cylinder since for this part a limit diameter is imposed.

- Chrome rings are not suitable for chrome cylinders... Often we forget about this restriction when we buy new segments.

-The major cause of oil consumption is not on this side... Very often, it is necessary to look at the valve guides, especially the exhaust ones, whose clearance is excessive on engines that do not heat up. And very often, the slags deposited on the exhaust valve stem contribute more to the wear of these guides. This is where you have to look for the cause of your technical problems because the pollution of the piston by unburned oil residues is a consequence and not a cause.
Since you have opened the engine, also remember to check the oil injector under the piston... There are sometimes interesting things that prevent the proper internal flow / cooling of the high engine.

[Guest]

7 hours ago, ukrsindicat@yahoo.com said:

Why did your client decide to pull the cylinder at all?

The engine was very old, had other issues and our local engine overhauler was going to be retiring, so they wanted him to overhaul it before he retired.

[A64Pilot]

On 9/26/2022 at 6:05 PM, M20Doc said:

I pulled this piston out of an O-360A1A with almost 2000 hours on it.  It always had good compression and not horrible oil consumption.

Yes, in this one the bottom two rings look fine, it might have gone awhile before things went South. It even looks as if it never had a top ring.

If you look at the first piston, especially the oil control ring was carboned up and therefore ineffective.

Perhaps all the first one needed was a “ring flush”?  

[Guest]

8 hours ago, A64Pilot said:

Yes, in this one the bottom two rings look fine, it might have gone awhile before things went South. It even looks as if it never had a top ring.

If you look at the first piston, especially the oil control ring was carboned up and therefore ineffective.

Perhaps all the first one needed was a “ring flush”?  

A giant cash flush cured all of its issues.

[Danb]

As always 

[Jim Peace]

Marvel Mystery oil.....

drop mic

 

 

[Shadrach]

On 9/26/2022 at 6:05 PM, M20Doc said:

I pulled this piston out of an O-360A1A with almost 2000 hours on it.  It always had good compression and not horrible oil consumption.

It looks like the fop ring was never installed… All I see is carbon. Were there at least parts of a ring hiding in all that build up?

Edit: Just saw you next post.

[cliffy]

On 9/16/2022 at 12:20 PM, A64Pilot said:

There is no logical reason why a prop strike inspection would require new bearings etc. But the manufacturer wrote the SB under the understanding that if the engine is torn down to that extent, it’s foolish to not go back with new bearings etc.

Just to be exact-  the PROP STRIKE AD does NOT require a complete tear down and inspection of the engine, It only requires the rear case removal and the crank gear inspection. Most all insurance companies pay for a complete tear down to limit their liability.

Lycoming's Required Parts to Replace SB is not legally binding on Pt 91 but it would be hard to support not doing it on the stand in front of a Judge or FAA in case of an accident _ "SO YOU know more than the manufacturer on how to overhaul this engine? "   Such a question HAS come up in other FAA proceedings.  

Prudent and legally binding are two different animals 

[kortopates]

...
Lycoming's Required Parts to Replace SB is not legally binding on Pt 91.
....

True, but following the manufacturer's overhaul manual IS required and you'll virtually always find the equivalent list of required parts replacement in it - even if not exactly the same vintage, since you don't have to follow the most recent edition.
But good points on being the focus of FAA investigation but I would be more concerned about a damaged party's lawyer suing you for essentially being negligent by not only replacing all required parts but also not complying with all service bulletins as any respected engine overhauler would do.


Sent from my iPhone using Tapatalk

[Guest]

The AD drives compliance with S/B 475C, gear inspection and bolt and lock plate replacement. Lycoming says to comply with S/B 533.

The AD seems overkill if you bumped your prop on the hangar door, but realistic if the prop tips are curled into a pretzel.

https://www.lycoming.com/sites/default/files/Crankshaft Gear Modification and Assembly Procedures.pdf

https://www.lycoming.com/sites/default/files/SB533C Recommended Action for sudden Engine Stoppage%2C Propeller_Rotor Strike or Loss of Propeller_Rotor Blade or Ti (1).pdf

[tmo]

I've read, on the internet, so take that into account, about people adding a pint of automotive Mobil 1 0W20 for a few hours / last flight before an oil change. It supposedly helps clean things up. What do the smart people here think, apart from it being obviously an unapproved approach. But I guess so is Camguard in turbocharged engines.

[EricJ]

4 hours ago, tmo said:

I've read, on the internet, so take that into account, about people adding a pint of automotive Mobil 1 0W20 for a few hours / last flight before an oil change. It supposedly helps clean things up. What do the smart people here think, apart from it being obviously an unapproved approach. But I guess so is Camguard in turbocharged engines.

I've not heard of using Mobil 1 for that, but it is not unusual, especially for certain engine types, to put some Marvel Mystery Oil (MMO) in the oil for the same purpose.   

[Guest]

12 hours ago, tmo said:

I've read, on the internet, so take that into account, about people adding a pint of automotive Mobil 1 0W20 for a few hours / last flight before an oil change. It supposedly helps clean things up. What do the smart people here think, apart from it being obviously an unapproved approach. But I guess so is Camguard in turbocharged engines.

I’d be cautious adding unknowns to my engine oil.  You’d hate to loosen enough stuff to block a gallery.  I remember years ago as an apprentice, an engine which had run on mineral oil for hundreds of hour got a quart of Aeroshell W100 added.  Shortly after the screen was blocked solid, followed by bearing failure.