Oil control rings and lessons learned - with pics!

[PT20J]

23 hours ago, canamex said:

 

@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...

We put one back together in the Lycoming factory class today. Instructor said to  put the gaps 120 deg apart with the oil ring gap toward the top of the engine.

Skip

[MikeOH]

27 minutes ago, PT20J said:

We put one back together in the Lycoming factory class today. Instructor said to  put the gaps 120 deg apart with the oil ring gap toward the top of the engine.

Skip

I've split the gaps, so to speak, on many auto engine rebuilds.  I certainly wouldn't assemble with them all lined up, but have wondered if they really stay put or randomly rotate over time.  I guess I should pay more attention during disassembly!

[carusoam]

30 minutes ago, MikeOH said:

I've split the gaps, so to speak, on many auto engine rebuilds.  I certainly wouldn't assemble with them all lined up, but have wondered if they really stay put or randomly rotate over time.  I guess I should pay more attention during disassembly!

Expect that there are forces on the rings that try to keep them moving…

If they stop rotating… it would probably start to show a heat pattern like when our valves stop rotating…

I can’t imagine what would cause them to turn… the cross hatches pattern doesn’t appear to imply a force one way or the other…

Anyone know a ring guy?  Or cylinder finish guy?

 

Mike,

Do you have a preference for engines you rebuild? (Chevy 350? 427?) 

Best regards,

-a-

[MikeOH]

Having a ring 'freeze' in its groove is a bad thing...they need to move.  I've always figured it was energy supplied by random vibrations with some slight asymmetry giving one rotational direction a slight preference over the other.

No preference...over the years single cylinder Briggs & Stratton (for my mini-bike), Chevy 6 230 ci, various small block Chevy's, one VW, MG (1600 cc), Triumph (also 1600 cc), ... no big blocks, however 

[canamex]

5 hours ago, A64Pilot said:

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

I'm in agreement here. It might be superstitious, but I decided to OH the #2 and #4 cylinders so that I would have a full set of matching cyliners, OH'd at close to the same time. If I were to replace the cylinders it would be with (ideally) a set of +.010 steel jugs for both the (debatable) extra HP as well as the suitability for my amount of flying. I likely won't get that opportunity as I'll most likely OH the motor with new steel jugs at some point, hopefully, in the furture.

[canamex]

4 hours ago, kortopates said:

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


Sent from my iPhone using Tapatalk

I would agree. It's a conversation I'm going to have with the mechanic who replaced all the seals/gaskets. Some peoples' prioritization schema are a little off. I'd much rather have a fully gone-through motor than a quickly rebuilt one.

[Guest]

Un less your maintainer has X-ray vision he could not see the stuck oil ring or the broken compression ring.  The real question is if you’re burning so much oil why didn’t he pull the pistons out of the cylinders?  What direction did you give him?  

[A64Pilot]

When I first joined this forum quite awhile ago I had a heated argument about a cracked case, one guy was saying just take all the parts out of the cracked case and put them in the serviceable case, leave the rods connected, don’t inspect anything, cam lifters etc.

I maintained that as an A&P I was required to determine the airworthiness of the parts before I put them into an engine, several came out and decried that no you only do what your told by the owner, that types like me are why it cost so much to have an airplane worked on, they would never take their airplane to a guy like me etc.

I still maintain that I have the requirement to determine serviceability / airworthiness of parts prior to installation.

If your completely disassembling a mid time or later engine and don’t replace the wear items, rings, bearings etc., your doing yourself a great dis-service. A very good way for an engine to run well beyond TBO is if the wear items have been replaced at mid life, often times that’s during a prop strike inspection.

I’d even consider a proper prop strike inspection to be a “light” overhaul. Many consider a prop strike as damage history, but I think if done correctly it actually can add value.

[dzeleski]

16 hours ago, A64Pilot said:

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

 

Although chamfer gets the point across I think the word you are looking for is cylinder choke.

 

Edit: Ignore me

[Shadrach]

On 9/16/2022 at 9:47 AM, A64Pilot said:

When I first joined this forum quite awhile ago I had a heated argument about a cracked case, one guy was saying just take all the parts out of the cracked case and put them in the serviceable case, leave the rods connected, don’t inspect anything, cam lifters etc.

I maintained that as an A&P I was required to determine the airworthiness of the parts before I put them into an engine, several came out and decried that no you only do what your told by the owner, that types like me are why it cost so much to have an airplane worked on, they would never take their airplane to a guy like me etc.

I still maintain that I have the requirement to determine serviceability / airworthiness of parts prior to installation.

If your completely disassembling a mid time or later engine and don’t replace the wear items, rings, bearings etc., your doing yourself a great dis-service. A very good way for an engine to run well beyond TBO is if the wear items have been replaced at mid life, often times that’s during a prop strike inspection.

I’d even consider a proper prop strike inspection to be a “light” overhaul. Many consider a prop strike as damage history, but I think if done correctly it actually can add value.

You may be referring to me as I had to split my case at 8XX hours due to a crack. A mechanic can take all the latitude they wish with regards to what they’re willing to do and what they’re  not willing to do. However, from a regulatory standpoint there is no requirement to inspect rod bearings during a case repair. If you decide to do that you will need to buy new rod bolts and if you’re going to do that, you might as well put new bearings in as well. Disassembling a functioning system that is not required for the repair is not necessary nor legally required. Whether or not it’s prudent to do so has nothing to do with the legal requirements. I believe in an individual mechanic’s right to determine what they are comfortable signing off and what they’re not. That comfort level will vary with personal experience, but they must all operate within the boundaries of the regs. In my case, the repairs were performed by an engine shop that turns out several overhauls each week. I had a long discussion with the owner of that shop prior to repair. We basically came up with a makes shift flow chart of what would be done and allowed for the potential of additional repairs and perhaps an overhaul if necessary. The over arcing philosophy applied was that there was no need to measure disassembled parts if they passed visual inspection and that there was no need to disassemble functioning parts just for the sake of disassembly. Given that the case was overhauled, we elected to replace any bearings that were housed in the freshly align bored case. It did not take a micrometer to see that the cam and crank showed almost no signs of use much less wear. The lifters looked normal to the naked eye but under magnification showed evidence of very minor pitting. We elected to replace the lifters, aforementioned main bearings and sent all four cylinders out for IRAN which included replacing one guide, lapping all the valves and lightly honing the cylinders. 
 

total cost of all the work was ~$4600 (2010) plus my time removing and hanging the engine. I had just parachuted out of a corporate job because of a merger and had the time on my hands.

I elected to go the route I did because I knew we were keeping the airplane and my priority was safety, not impressing a potential buyer with TTSMOH numbers.

It turned out to be the best choice. I learned a lot about my airplane and took great time and care with routing hoses and controls while hanging the engine.

That was 11 years and 5XX ago. The engine has run flawlessly since and remains oil tight. I could’ve easily spent 40k and received zero additional return for 10X outlay…or worse if there was a problem after overhaul. Many of the armchair experts on the AOPA red board voiced their opinions that an overhaul was the only prudent course of action. Time has proven otherwise.

[Shadrach]

10 minutes ago, dzeleski said:

 

Although chamfer gets the point across I think the word you are looking for is cylinder choke.

Nope, he meant chamfer. He’s referring to an angle that is machined into the flange at the bottom of the cylinder where the piston is inserted, not the taper of the piston walls (choke).

[dzeleski]

25 minutes ago, Shadrach said:

Nope, he meant chamfer. He’s referring to an angle that is machined into the flange at the bottom of the cylinder where the piston is inserted, not the taper of the piston walls (choke).

Brain wasnt fully awake, thanks thats correct.

[canamex]

4 hours ago, M20Doc said:

What direction did you give him?

The decision to replace all the gaskets and seals came after a series of visits to the plane to chase oil leaks which felt like playing an expensive game of whack-a-mole. As soon as we fixed one little oil seep, another one would pop up, and another, and another.

Additionally it became pretty clear that anything organic around the engine was disintegrating, so after replacing everything we could, including mounts, baffles, SCAT tubing, and all of the hoses, and still having leaks, the next logical thing to focus on was the leaks stemming from the bases of the cylinders. This course of action was based on many conversations with my mechanic in which the plan was to minimize down time (I fly the plane a lot, and sometimes for work), and gradually replace anything organic, that is, seals and gaskets and hoses. Because the oil consumption was still within limits and my understanding was that chromed cylinders just naturally use more oil, it wasn't inconceivable to think that the high oil consumption was due to a combination of chromed cylinders and pesky leaks. So if baseline for Chromed cylinders was 1qt/4hrs maybe I was leaking 1qt/hr from everything else.

What I know now, after a few months and many conversations with engine shops and more mechanics is that the numbers just don't add up. Properly installed and broken-in chromed cylinders should not be burning any more than 1qt/7-8hrs and there's no way the oil leaks we were chasing were contributing more than 1qt/hr.

So, should my mechanic have raised his hand and explored the cylinder further? Absolutely yes. When I asked about the cylinder in question, his guidance was that the seals and gaskets would fix the issue. The mechanic in Yellowknife discovered a host of issues with how the motor had been put back together including improperly torqued hoses, improperly sized clamps, non aviation grade hardware, improper routing of the fuel lines...we're no longer working together.

@Shadrach's decision making process seems similar to mine, and I'm still well under half the cost of an overhaul. Time will now tell as to if I'm so lucky to have the same results...

[Shadrach]

13 hours ago, MikeOH said:

Having a ring 'freeze' in its groove is a bad thing...they need to move.  I've always figured it was energy supplied by random vibrations with some slight asymmetry giving one rotational direction a slight preference over the other.

No preference...over the years single cylinder Briggs & Stratton (for my mini-bike), Chevy 6 230 ci, various small block Chevy's, one VW, MG (1600 cc), Triumph (also 1600 cc), ... no big blocks, however 

Rings move but I don’t think it really matters much as any metal to metal contact between cylinder wall and ring  is minimal after break in. Honda experimented with oval pistons back in the 70s. They essentially took a small V8 block and paired the combustion chambers to get around the cylinder limits imposed by Grand Prix rules. 

[Fly Boomer]

17 hours ago, A64Pilot said:

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

I have worked on engines with such a deep chamfer that my ring compresser would not work.

[Shadrach]

3 minutes ago, Fly Boomer said:

I have worked on engines with such a deep chamfer that my ring compresser would not work.

I’m confused as to how a chamfer at the flange would prevent a ring compressor from functioning.

[Fly Boomer]

22 minutes ago, Shadrach said:

I’m confused as to how a chamfer at the flange would prevent a ring compressor from functioning.

The adjusting mechanism would contact the edge if the barrel before the spring steel could get to the “bottom” of the chamfer.  You had to be there.

[Shadrach]

31 minutes ago, Fly Boomer said:

The adjusting mechanism would contact the edge if the barrel before the spring steel could get to the “bottom” of the chamfer.  You had to be there.

You’re saying the rings would pop out of the compressor and expand slightly in the chamfered area rather than slide into the barrel?

[A64Pilot]

1 hour ago, Shadrach said:

I’m confused as to how a chamfer at the flange would prevent a ring compressor from functioning.

Most ring compressors are bands and have small detents in them to keep the band from sliding in between the piston and cylinder, these detents should catch the lip of the cylinder liner.

A nice chamfer is wider than these bumps and they will not catch the edge of the barrel and will slide in under the chamfer, then it binds up and compresses the piston so it’s tough to slide.

[Shadrach]

14 minutes ago, A64Pilot said:

Most ring compressors are bands and have small detents in them to keep the band from sliding in between the piston and cylinder, these detents should catch the lip of the cylinder liner.

A nice chamfer is wider than these bumps and they will not catch the edge of the barrel and will slide in under the chamfer, then it binds up and compresses the piston so it’s tough to slide.

I wouldn’t know. I just used hose clamps on small displacement piston engines I’ve assembled and thos go in from the top.  
I did help install a few cylinders on C150 (cont O200) years ago but I don’t recall a ring compressor being used. 

[A64Pilot]

3 hours ago, Shadrach said:

You may be referring to me as I had to split my case at 8XX hours due to a crack. A mechanic can take all the latitude they wish with regards to what they’re willing to do and what they’re willing not to do. However, from a regulatory standpoint there is no requirement to inspect rod bearings during a case repair. If you decide to do that you will need to buy new rod bolts and if you’re going to do that, you might as well put new bearings in as well. Disassembling a functioning system that is not required for the repair is not necessary nor legally required. Whether or not it’s prudent to do so has nothing to do with the legal requirements. I believe in an individual mechanics right to determine what they are comfortable signing off and what they’re not. That comfort level will vary with personal experience. In my case, the repairs were performed by an engine shop that turns out several overhauls each week. I had a long discussion with the owner of that shop prior to repair. We basically came up with a makes shift float chart of what would be done and allowed for the potential of additional repairs and perhaps an overhaul if necessary. The over arcing philosophy applied was that there was no need to measure disassembled parts if they passed visual inspection and that there was no need to disassemble functioning parts just for the sake of disassembly. Given that the case was overhauled, we elected to replace any bearings that were housed in the freshly align bored case. It did not take a micrometer to see that they cam and crank showed almost no signs of use much less wear. The lifters looked normal to the naked eye but under magnification showed evidence of very minor pitting. We elected to replace the lifters, aforementioned main bearings and sent all four cylinders out for IRAN which included replacing one guide, lapping all the valves and lightly honing the cylinders. 
 

total cost of all the work was ~$4600 Plus my time removing and hanging the engine. I had just parachuted out of a corporate job because of a merger and had the time on my hands.

I elected to go the route I did because I knew we were keeping the airplane and my priority was safety, not impressing a potential buyer with TTSMOH numbers.

It turned out to be the best choice. I learned a lot about my airplane and took great time and care with routing hoses and controls while hanging the engine.

That was 11 years and 5XX ago. The engine has run flawlessly since and remains oil tight. I could’ve easily spent 40k and received zero additional return for 10X outlay…or worse if there was a problem after overhaul. Many of the armchair experts on the AOPA red board voiced their opinions that an overhaul was the only prudent course of action. Time has proven otherwise.

I had no idea who it was, slept several times since.

I disagree, Someone can’t bring me a box of parts and say assemble an engine from these, I have to have either tags or some other form of proof that they meet specs and are airworthy, or determine their airworthiness myself, which many I can’t they have to go off for that.

As I disassemble an engine the parts are cleaned and inspected and should be tagged. I just can’t fathom going through and paying for all that labor and not putting in new bearings. Many argue that you should never under any circumstances replace a tire and reuse the tube and I can’t argue against that. But where do you draw the line on an engine, do you reuse the garloc seals and prop seal, they weren’t leaking before.

As with all rules it gets a little loose, for example if I pull a prop to replace an alternator belt you don’t send the prop off to be disassembled and inspected. Some would say you have to use common sense.

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.

If you pull a cylinder for whatever reason, it should be inspected, and I maintain an A&P is required to. 

If a mechanic puts a cracked exhaust back on after a cylinder change and the pilot dies from CO poisoning, is the mechanic liable? Should he sleep well at night?

 

[Shadrach]

9 minutes ago, A64Pilot said:

I had no idea who it was, slept several times since.

I disagree, Someone can’t bring me a box of parts and say assemble an engine from these, I have to have either tags or some other form of proof that they meet specs and are airworthy, or determine their airworthiness myself, which many I can’t they have to go off for that.

As I disassemble an engine the parts are cleaned and inspected and should be tagged. I just can’t fathom going through and paying for all that labor and not putting in new bearings. Many argue that you should never under any circumstances replace a tire and reuse the tube and I can’t argue against that. But where do you draw the line on an engine, do you reuse the garloc seals and prop seal, they weren’t leaking before.

As with all rules it gets a little loose, for example if I pull a prop to replace an alternator belt you don’t send the prop off to be disassembled and inspected. Some would say you have to use common sense.

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.

If you pull a cylinder for whatever reason, it should be inspected, and I maintain an A&P is required to. 

If a mechanic puts a cracked exhaust back on after a cylinder change and the pilot dies from CO poisoning, is the mechanic liable? Should he sleep well at night?

 

A box of parts is not the same thing as an otherwise operational and airworthy engine with complete logs that is in need of an obvious repair.

No need for every mechanic to agree on what's prudent, though it'd be nice if they agreed on what is legal. Clearly my engine shop felt comfortable with the scope of work they performed. I followed their recommendations which were made based on my goals.  Another forum member had a similar issue to mine and elected to use the same shop because of my experience. For whatever reason the same shop owner recommended an OH after splitting the case... Don't know the details but I am guessing he had a good reason.

[Fly Boomer]

1 hour ago, Shadrach said:

You’re saying the rings would pop out of the compressor and expand slightly in the chamfered area rather than slide into the barrel?

Yes!  The spring compressor was an obstacle to getting the job done.

[PT20J]

In my class we used the Lycoming factory tool to compress rings. It’s a heavy machined steel ring with a slot to go over the rod and a ramp machined into the inside circumference on the engine side. It’s fast since you don’t have to tighten any clamps - just press it on over the piston and slip the cylinder on. Instructor said Lycoming sells them for $6500. That’s probably why I’ve never seen one before. 

[Guest]

5 hours ago, PT20J said:

In my class we used the Lycoming factory tool to compress rings. It’s a heavy machined steel ring with a slot to go over the rod and a ramp machined into the inside circumference on the engine side. It’s fast since you don’t have to tighten any clamps - just press it on over the piston and slip the cylinder on. Instructor said Lycoming sells them for $6500. That’s probably why I’ve never seen one before. 

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