Oil control rings and lessons learned - with pics!

[canamex]

Hey Mooneyspacers,

Just received a picture of my #4 piston and thought I'd share the backstory.

In the last 18 months of owning my 1967 M20F, I've flown just under 400 hours and the entire time have been chasing high oil consumption. I got the plane at a decent price and did a what I thought was a thorough pre-buy, although as a first time owner I definitely know more now than I did last year at this time. The IO-360-A1A had 995 hours on it when I bought it, was last overhauled in 1982, and had two overhauled chromed cylinders put on it five months before I purchased the aircraft, replacing the #1 & #3 cylinders.

About six months ago I got tired of chasing messy oil leaks and decided to take the motor off the plane and replace all of the gaskets and seals that we could without splitting the case. Why didn't I just do a major overhaul? I got an incredibly good deal and my thinking was, "well the engine hasn't been overhauled since 1982, it's been in New Mexico all of its life, and replacing everything which is organic and could suffer from dry-rot might get me another 1000 hours out of the motor". At my price, it was only a few bucks per hour of life extension. While I had the cylinders off, we took a good look at the case and cam and everything looked perfect.

The thing is, once I got flying again, while the motor was much cleaner than before, my oil consumption was still around 4hrs/qt. I read pretty much every post here, as well as anything else I could find about IO-360's, and I resigned myself to high oil consumption due to the engine having chromed cylinders.

In mid-July, I departed Mexico City for Oshkosh and began to notice oil on the gear. Oil consumption was now about 3hrs/qt. By the time I arrived in St. Paul, it was at 2hrs/qt. Before the engine work I had been flying quite a bit at 2hrs/qt and some mechanics I spoke with told me that it was acceptable and that I shouldn't worry too much. Oil consumption stayed steady at 2hrs/qt St. Paul and Regina, SK, and all the way up to northern Saskatchewan. Then, leaving Athabasca Lake for Yellowknife, NWT, I dropped 4 quarts in 2 hours, landed the plane, and called a mechanic.

A friendly mobile Quebecois AME (A&P in Canada) spent a couple of days on the plane re-torquing almost everything and fixing things which had broken because of careless re-assembly of the motor/accessories/cowl and we got the plane back to 2hrs/qt. We departed and flew south through Alberta and actually improved consumption to 4hrs/qt over the last couple of flights before arriving home in Victoria the next day.

I then started up the plane for a sightseeing flight and noticed the engine running very rough, had a bad feeling and took it into the folks at Victoria Air Maintenance. They found a stuck exhaust valve on cylinder #4, un-stuck-it, I flew it, but oil consumption was horrible and the oil temp and pressure gauges were high and low yellow positions respectively. Knowing I'd have to be flying over water and the Sierras to get back to Mexico City, I decided to have them pull the #2 & #4 cylinders to get overhauled.

Just received this picture of the #4 piston and as you can see, the oil control ring is completely embedded into the piston. Will update as things progress.

[N201MKTurbo]

A ring flush probably would have helped.

I was always skeptical of the procedure, but did it on a 310 last year and it did wonders for it.

[Shadrach]

I am confused. You say you had the cylinders off to replace the gaskets and got a good look at the internals. Reassembled everything and the oil control ring coked up that bad in a few hundred hours?

[carusoam]

Got an engine monitor to go with that?

The stuck valve should show up in the data…

Have you taken any pics inside the cylinders?

Silly cylinder behavior, and valve behavior can be seen in pics…

Good pics can be done with low dollar dental cameras…

PP thoughts only,

-a-

[N201MKTurbo]

3 hours ago, canamex said:

Hey Mooneyspacers,

Just received a picture of my #4 piston and thought I'd share the backstory.

In the last 18 months of owning my 1967 M20F, I've flown just under 400 hours and the entire time have been chasing high oil consumption. I got the plane at a decent price and did a what I thought was a thorough pre-buy, although as a first time owner I definitely know more now than I did last year at this time. The IO-360-A1A had 995 hours on it when I bought it, was last overhauled in 1982, and had two overhauled chromed cylinders put on it five months before I purchased the aircraft, replacing the #1 & #3 cylinders.

About six months ago I got tired of chasing messy oil leaks and decided to take the motor off the plane and replace all of the gaskets and seals that we could without splitting the case. Why didn't I just do a major overhaul? I got an incredibly good deal and my thinking was, "well the engine hasn't been overhauled since 1982, it's been in New Mexico all of its life, and replacing everything which is organic and could suffer from dry-rot might get me another 1000 hours out of the motor". At my price, it was only a few bucks per hour of life extension. While I had the cylinders off, we took a good look at the case and cam and everything looked perfect.

The thing is, once I got flying again, while the motor was much cleaner than before, my oil consumption was still around 4hrs/qt. I read pretty much every post here, as well as anything else I could find about IO-360's, and I resigned myself to high oil consumption due to the engine having chromed cylinders.

In mid-July, I departed Mexico City for Oshkosh and began to notice oil on the gear. Oil consumption was now about 3hrs/qt. By the time I arrived in St. Paul, it was at 2hrs/qt. Before the engine work I had been flying quite a bit at 2hrs/qt and some mechanics I spoke with told me that it was acceptable and that I shouldn't worry too much. Oil consumption stayed steady at 2hrs/qt St. Paul and Regina, SK, and all the way up to northern Saskatchewan. Then, leaving Athabasca Lake for Yellowknife, NWT, I dropped 4 quarts in 2 hours, landed the plane, and called a mechanic.

A friendly mobile Quebecois AME (A&P in Canada) spent a couple of days on the plane re-torquing almost everything and fixing things which had broken because of careless re-assembly of the motor/accessories/cowl and we got the plane back to 2hrs/qt. We departed and flew south through Alberta and actually improved consumption to 4hrs/qt over the last couple of flights before arriving home in Victoria the next day.

I then started up the plane for a sightseeing flight and noticed the engine running very rough, had a bad feeling and took it into the folks at Victoria Air Maintenance. They found a stuck exhaust valve on cylinder #4, un-stuck-it, I flew it, but oil consumption was horrible and the oil temp and pressure gauges were high and low yellow positions respectively. Knowing I'd have to be flying over water and the Sierras to get back to Mexico City, I decided to have them pull the #2 & #4 cylinders to get overhauled.

Just received this picture of the #4 piston and as you can see, the oil control ring is completely embedded into the piston. Will update as things progress.

The top ring looks broken, and the broken piece is in the ring groove.

[carusoam]

+1 for ring gaps… they are usually quite tiny… just enough space for thermal expansion…

Eagle eye award… goes to Rich today!

Best regards,

-a-

[canamex]

On 9/13/2022 at 7:29 PM, N201MKTurbo said:

A ring flush probably would have helped.

I was always skeptical of the procedure, but did it on a 310 last year and it did wonders for it.

I have the savvy aviation PDF for that procedure and considered it but not sure that it would have done much to un-stick that oil control ring. Between my two test-flights and at the recommendation of both the mechanic as well as two cylinder overhaul shops, I did add a quart of the Marvin's Marvelous Mystery Oil to see what would happen but the oil consumption just got worse.

[canamex]

On 9/13/2022 at 7:40 PM, Shadrach said:

Reassembled everything and the oil control ring coked up that bad in a few hundred hours?

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.

[canamex]

On 9/13/2022 at 8:08 PM, carusoam said:

Got an engine monitor to go with that?

The stuck valve should show up in the data…

Have you taken any pics inside the cylinders?

Silly cylinder behavior, and valve behavior can be seen in pics…

Good pics can be done with low dollar dental cameras…

PP thoughts only,

-a-

@carusoam An engine monitor is next up on the list but with all the engine costs the past month I might not be installing until the new year. There's also a GPS, new panel, interior, paint...all in time

@N201MKTurbo nice eyes! My understanding is that the rings gaps should be rotated 90° from eachother and it doesn't seem that's the case either...

[Shadrach]

1 hour ago, 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.

Opportunity lost. Maybe it’s common practice to leave pistons in cylinders during removal.   I would think a mx would want to put eyes on the rings of an engine that is  burning oil.

[carusoam]

Also…

Usually… rings are free to rotate around the pistons…

On odd days they can align… so if you get a bad compression reading… going to fly again often is enough to have the rings un-align…

With this much oil going through the cylinder…

The engine monitor will probably see when a lower spark plug is getting flooded… or the oil’s ash blocks the gap…

Stuck valves… don’t rotate the way they are supposed to… these have a signature in the EGT patterns that look like a sawtooth…

There are often good engine monitors that show up for sale around here… it doesn’t need to be a nice color one or of primary type…

The expensive part is the installation… so pick one similar to what you want in the future… and build on it…

PP thoughts only, not a mechanic..
 

Best regards,

-a-

[EricJ]

14 hours ago, canamex said:

I have the savvy aviation PDF for that procedure and considered it but not sure that it would have done much to un-stick that oil control ring. Between my two test-flights and at the recommendation of both the mechanic as well as two cylinder overhaul shops, I did add a quart of the Marvin's Marvelous Mystery Oil to see what would happen but the oil consumption just got worse.

A little bit of MMO may have just removed a little gunk and opened up more space for leaks.    The full procedure can clear sufficient crud out of the control ring and lands that it can move in the groove and seat again, which is the potential cure.   When it works, it saves a ton of expense.

The broken compression ring means it was a good idea to take it out, anyway, so the oil ring condition is kind of moot.   As mentioned, the rings can rotate, so they can be in a random orientation on removal regardless of how they were put in.

[ArtVandelay]

Can this problem be avoided by running LOP, less excess avgas especially unburned avgas, cleaner running engine?

[DXB]

14 hours ago, 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.

Something doesn't make sense to me here.  I have no idea how one would remove a cylinder without seeing the entire piston including the rings. One normally takes off the cylinder first. Then one taps out the piston pin to remove the piston.  One could leave the piston in place on the connecting rod if the only goal was to inspect the bottom end, but I think it's typical to replace the rings and rehone the cylinder barrel to ensure everything seats up once the cylinder goes back on.  My mechanical knowledge is a bit suspect however - someone please correct me if needed.

[Guest]

14 hours ago, 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.

The Chrome cylinder walls won’t have helped either.

[Shadrach]

1 hour ago, ArtVandelay said:

Can this problem be avoided by running LOP, less excess avgas especially unburned avgas, cleaner running engine?

Don't see how mixture would matter. Oil consumption is not a function of mixture. I would guess that the broken compression ring preceded the oil control ring.

[Shadrach]

1 hour ago, DXB said:

Something doesn't make sense to me here.  I have no idea how one would remove a cylinder without seeing the entire piston including the rings. One normally takes off the cylinder first. Then one taps out the piston pin to remove the piston.  One could leave the piston in place on the connecting rod if the only goal was to inspect the bottom end, but I think it's typical to replace the rings and rehone the cylinder barrel to ensure everything seats up once the cylinder goes back on.  My mechanical knowledge is a bit suspect however - someone please correct me if needed.

You can pull the cylinder just far enough off to access the pin and leave the rings still compressed in the barrel.  

[DXB]

14 minutes ago, Shadrach said:

You can pull the cylinder just far enough off to access the pin and leave the rings still compressed in the barrel.  

Interesting - good to know in case one pulls a cylinder purely to examine the bottom end.  

[Shadrach]

30 minutes ago, DXB said:

Interesting - good to know in case one pulls a cylinder purely to examine the bottom end.  

That is the likely what transpired and the reason that the pistons were left in the barrel. Not needing to bother with a ring compressor during reassembly speeds up the process. However, I am surprised the mechanic was not curious about the dark carbon deposits on the piston skirt. It's pretty clear that something was not functioning properly.

[kortopates]

1 hour ago, Shadrach said:

You can pull the cylinder just far enough off to access the pin and leave the rings still compressed in the barrel.  

Only in theory. Reality is once the piston has any time in service the pin gets coked with enough carbon on the pin that it will no longer move without being pressed out by a tool, or other similar fashion, that can't be accomplished while your still holding the cylinder with both hands. After the cylinder comes off, the piston pin can be pressed out. But it won't go back on with just a finger push till it's cleaned up.

Taping out the piston pin is no-no for putting a side-load on the crankshaft rod bearing. So is (re) installing an unairworthy cylinder, regardless if it just came off. Just say'n...

 

[Shadrach]

4 minutes ago, kortopates said:

Only in theory. Reality is once the piston has any time in service the pin gets coked with enough carbon on the pin that it will no longer move without being pressed out by a tool, or other similar fashion, that can't be accomplished while your still holding the cylinder with both hands. After the cylinder comes off, the piston pin can be pressed out. But it won't go back on with just a finger push till it's cleaned up.

Taping out the piston pin is no-no for putting a side-load on the crankshaft rod bearing. So is (re) installing an unairworthy cylinder, regardless if it just came off. Just say'n...

 

I was not advocating.  I’ve not had problems pressing pins out of non aviation, air cooled piston engines (mostly British twins). Given the pics the OP posted, I assumed that the OP’s mechanic some how accomplished what you’re suggesting is no no…

[Guest]

3 hours ago, Shadrach said:

That is the likely what transpired and the reason that the pistons were left in the barrel. Not needing to bother with a ring compressor during reassembly speeds up the process. However, I am surprised the mechanic was not curious about the dark carbon deposits on the piston skirt. It's pretty clear that something was not functioning properly.

You can put a ringed piston in a Lycoming barrel without a ring compressor.

[N201MKTurbo]

28 minutes ago, M20Doc said:

You can put a ringed piston in a Lycoming barrel without a ring compressor.

If it has used rings, it sometimes lets the blood out of your fingers.

[A64Pilot]

36 minutes ago, M20Doc said:

You can put a ringed piston in a Lycoming barrel without a ring compressor.

Done it with my fingernails, the cylinder has a chamfer if I use the word right, I prefer doing it this way because you can feel if a ring gets caught as very little pressure is used to push the piston in. Just rock the piston slightly to keep it level

Same with 4 cyl Kawasaki’s, never used a compressor there either. There you have to do two cylinders at the same time

So far as leaving the piston in, some do and claim there is no requirement to inspect the cylinder and piston for airworthiness either, but I do, and to be honest unless everything looks brand new the cylinder is going to the shop for a light hone and I’m fitting new rings, depending on its age it may get new valves and valve guides too, yeah it’s some money, but you can breathe a lot of hours into a cylinder doing so. I don’t have the equipment to hone correctly and I will not use a dingleberry hone, done right honing is a very precise process,,and a dingleberry is anything but precise.

It’s common practice to stagger ring gaps, but I’m not so sure it does any good because they do rotate, except two strokes that have a pin in the piston that prevents rotation. I still stagger them, because it might help and certainly isn’t hard to do.

Oh, do yourself a favor and plan on retiring the chrome cylinders

[kortopates]

I was not advocating.  I’ve not had problems pressing pins out of non aviation, air cooled piston engines (mostly British twins). Given the pics the OP posted, I assumed that the OP’s mechanic some how accomplished what you’re suggesting is no no…

Understand. It’s a mystery to me how that cylinder got put back on without noticing the stuck ring.


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