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Loss Of Oil Pressure caused by a broken ring

gasman

Well Known Member
Friend
Caused a dead stick landing at night. Dec. 2021 FLYING "I learned about flying from that" page 24, A broken ring in number 6 cylinder caused a loss of all oil pressure and total engine failure.

So, my question is.... If the rings are not part of the pressure system, how can a broken ring cause total loss of oil pressure unless the broken ring caused that jug to burn down all of the oil to the point of low oil level and no oil pressure?

Has anyone had a broken ring that caused loss of all oil pressure, and or total failure of the engine?
 
Broken ring can cause increased crankcase pressure that forces oil out the vent ---maybe even blow out the front seal.
 
Huh? too

Yeah, I noticed that in the article, too. I suppose a broken ring could raise crankcase pressure, but it's hard to imagine it getting so high from such a failure in one cylinder that it would push oil out. I'm bumfuzzled. My best guess is the pilot misheard or misunderstood something a mechanic said.
 
Excessive crank case pressure can push out a front main seal which will lead to rapid oil loss.
 
So to get to an actual link to oil pressure - if there is no oil, then no pressure can be developed.

But broken rings don't do this, lack of oil does resulting from
a cascade of failures.

The greater question is why was the broken ring not found sooner?

I had a broken compression ring in my 540. Completely unnoticeable and only found with a compression test. No detectable performance increase after replacement. Blowby was a bit higher than normal, but still not a lot of oil on the belly.

I agree that a broken ring, in and of itself cannot cause a loss of oil pressure. I suspect that two broken comp rings could possibly raise CC pressures by a lot, but should create noticeable piston rattling noise.

Larry
 
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It can, ask me why I know....

One weekend I was breaking in a cylinder after having it reworked due to broke rings and higher oil consumption. On Saturday I flew for several hours from Madison WI to Sikeston MO for lunch at Lambert's Cafe with a friend and returned with no issues. The next day, Sunday, decided to go West to Amana IA to visit another friend. After stopping there I flew North into Minnesota almost to the twin cities then tuned back towards home. An hour from home I stopped for fuel, all seemed good so far. The last hour flight home was uneventful and did not notice any loss of power.

When I got out of the plane was I surprised, I had oil all over the tail of the airplane, LOTS OF IT. I had two of the other cylinders with broken rings and in the last hour they pumped out a couple quarts of oil out the crank case vent. I don't know if this started immediately upon take off in the last hour of flight or just 10 minuets before landing. What I do know is, if this had happened earlier on one of my longer legs that weekend my engine would most likely have lost all of it's oil and thus oil pressure. The engine could have been toast.

You might wonder why rings broke in 3 cylinders in such a short time. The shop who reworked my cylinders could not tell my why for sure. I believe it may have resulted from a problem some time earlier with high CHT's due to Mags going out of time. I did not understand the cause and ran the engine too long with this condition before I diagnosed the problem. Mistake number two was not having all the cylinders reworked after I found the first one with a broken ring.
 
You might wonder why rings broke in 3 cylinders in such a short time. The shop who reworked my cylinders could not tell my why for sure..

Some rings (Superior, for example) do not come sized to fit. They are manufactred to at least the largest possible diameter and must be filled to a specific end gap at a specific place in the cyl bore; Instructions are on their website and a warning comes in the box. Cutting the choke in the bore is an imprecise process and a decent amount of variability exists across cylinders. I believe some other manufacturers's rings are sized to fit, so it's easy to make a mistake. I am guessing your mechanic didn't measure and fit them and the first time you had elevated combustion temps (as combustion temps rise, the rings expand) beyond what the gaps could handle, the rings broke from lack of a gap. Ring gap is very important and the first time that the gap goes to zero, the rings snap.

If 3 out of 4 cylinders have cracked rings, it is a pretty good assumption that the engine builder didn't measure the ring gaps. Kind of sad, as this is engine building 101. If the Lycoming specified minimum ring gap is honored, the engine will go to 500* CHT without broken rings.

Larry
 
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Poor technique installing the rings on the piston could increase the potential for ring failure, also
 
Key Event - thanks for sharing

One weekend I was breaking in a cylinder after having it reworked due to broke rings and higher oil consumption. On Saturday I flew for several hours from Madison WI to Sikeston MO for lunch at Lambert's Cafe with a friend and returned with no issues. The next day, Sunday, decided to go West to Amana IA to visit another friend. After stopping there I flew North into Minnesota almost to the twin cities then tuned back towards home. An hour from home I stopped for fuel, all seemed good so far. The last hour flight home was uneventful and did not notice any loss of power.

When I got out of the plane was I surprised, I had oil all over the tail of the airplane, LOTS OF IT. I had two of the other cylinders with broken rings and in the last hour they pumped out a couple quarts of oil out the crank case vent. I don't know if this started immediately upon take off in the last hour of flight or just 10 minuets before landing. What I do know is, if this had happened earlier on one of my longer legs that weekend my engine would most likely have lost all of it's oil and thus oil pressure. The engine could have been toast.

You might wonder why rings broke in 3 cylinders in such a short time. The shop who reworked my cylinders could not tell my why for sure. I believe it may have resulted from a problem some time earlier with high CHT's due to Mags going out of time. I did not understand the cause and ran the engine too long with this condition before I diagnosed the problem. Mistake number two was not having all the cylinders reworked after I found the first one with a broken ring.

Advanced timing can not only give high CHT, but very high piston temps causing skirt scuffing. That aluminum transfer to the walls will stick rings and yield a lot of blow-by. High probability that broken rings were a result of this and nothing to do with the cylinders, new or old.

I might guess your engine does not have oil jets under the pistons?

edit: Sorry for any confusion - -oil cooling jets will do just that - cool the pistons. If timing was really high the elevated temps will cause high piston and barrel temps , reducing the oil film and softening aluminum and allowing transfer between the piston and wall. Jets would reduce these temps and reduce the probability of scoring. Jets have virtually no connection to causing oil ring or compression ring breakage, but could aid in breaking the over temperature failure cascade leading to stuck and/or broken rings. I hope that makes better sense.
 
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Wonder how effectively my AntiSplat crank vacuum gizmo would mitigate the blow-by pressurization if a ring broke.
 
Advanced timing can not only give high CHT, but very high piston temps causing skirt scuffing. That aluminum transfer to the walls will stick rings and yield a lot of blow-by. High probability that broken rings were a result of this and nothing to do with the cylinders, new or old.

I might guess your engine does not have oil jets under the pistons?

I don't know if I have the jets or not, but with proper timing I have no issue with overheating.
 
My cylinders are currently removed for overhaul due to a broken ring.

My oil temps had been running higher than normal all summer. I presumed it was due to warm weather operations. Looks more likely due to blow by.
My oil consumption went from a quart every 5 hours or so to a quart every hour or two; this change in oil consumption was acute between one flight and the next.
Compression test showed 75+ all around. Engine was still producing good power. It had an occasional hickup transient loss of power. Strangely, when I blew into the air-oil separator I could hear an air leak from somewhere near the front of the motor, and a quarter turn of the prop would make it come and go. I still don't understand what was causing this; it wouldn't replicate when I got the plane to my mechanic.
I decided to investigate. We found a broken ring on cylinder #3. It's spark plugs were slightly oily. Engine is a Titan X-340 with approx 350 TTSN

Advanced timing can not only give high CHT, but very high piston temps causing skirt scuffing. That aluminum transfer to the walls will stick rings and yield a lot of blow-by. High probability that broken rings were a result of this and nothing to do with the cylinders, new or old.

I might guess your engine does not have oil jets under the pistons?

My engine lacks oil squirters. Not sure if that is related to the ring breaking. Just citing as a data point. My CHT's never go above 400; they typically max out in the 390 range during climbs. Standard mags timed 25 degrees.

Wonder how effectively my AntiSplat crank vacuum gizmo would mitigate the blow-by pressurization if a ring broke.

I have an AntiSplat exhaust air valve with the Napa CRB 229000 valve. There was still enough pressurization that oil was being pushed out the whistle slot in the hose leading to the exhaust air valve.

I have done some reading as to possible causes of broken rings. Many possible causes...
This may have been a ring flutter incident. As slippery as this plane is, I do occasionally close the throttle and flatten the prop pitch in descent. If I haven't done that in descent, it is always done in the pattern or prep for landing. I found some mentioning this practice as bad such as here:
https://forum.cubcrafters.com/showthread.php/2256-Engine-management
https://www.euroga.org/forums/maint...ter-applicable-to-our-aircraft-engines?page=1

And then there's this:
The Titan service letter for ring installation comes with this bold warning:
http://www.continental.aero/xPublications/xService Bulletins/Experimental PMA/SIL004/
WARNING
Hard bumping of the piston ring during installation can cause
the formation of cracks in the piston ring that may not fail
immediately; however, piston ring breakage can introduce
pieces of the ring expander between the piston and bore. This
can result in the formation of grinding type cracks on the bore
surface and may cause complete catastrophic engine failure.

In reading I found an educated post on another forum by Kevin Mead:
https://www.pilotsofamerica.com/community/threads/lycoming-stuck-ring.67359/page-2
We have this problem all of the time with the Mirage and Matrix Lycoming engines. At first nobody wants to believe it's a cylinder problem. I have found the oil control ring stuck, but in most cases it's broken.

The oil consumption will drop immediately, normally as bad as 1 qt per hour. I've seen one broken oil ring cause a consumption of 4 qts in an hour. The 2 compression rings will be good and the compression check will be 80/80. There is so much oil in the cylinder leading to great compression. Another symptom will be a bad mag check on the first flight of the day. Oil consumption is at it's worst in the flight levels too.

What's funny is that I can pull pieces of the oil control ring and it's spring out of the suction screen but the cylinder wall is not damaged.

I had two calls in the last month about sudden high oil consumption on the Lycoming TIO540 engine. So much consumption that they landed with very little oil. In both cases it was a broken oil control ring. Sudden consumption has been a bad turbo many times too, oil loss is so fast in those cases. This problem has been going on since the introduction of the new chrome edge cast iron oil control rings in 1994, So many times the people that where forced down continued flight after adding 6 qts of oil or more at the last stop.

My common findings.

Compression will be good. There's extra oil providing a better seal.

Normally a bad mag check, oil on a plug. An engine monitor will take you to the offending cylinder.

Many times pieces of the oil control ring are in the suction screen.

Normally the cylinder wall isn't damaged, I don't know how.

I find the rings broken in the box that is in a new cylinder kit.

I have also had the same problems on the Turbo Saritoga and the Machen converted Aerostar TIO540-S1AD and -U2A engines.

Want to see higher consumption? Take it up high.

Many of the people that continued flight had a dead and destroyed engine by the time they made it down from the flight levels.

The training must be good, very few off field emergency landings.

It's really bad that nothing has been done to end this problem.


Kevin states sudden high oil consumption. This is important as it was the case with my broken ring. While I don't know when the ring broke, I did see sudden high oil consumption. It changed from a quart every 5-6 hours to a quart an hour the next flight. I also had an oily plug on the #3, the cylinder with the broken ring. The compression test was 75+/80 on all cylinders in spite of the broken ring. I would suggest that a broken ring be high on ones differential diagnosis list when confronted with these symptoms. Unfortunately, the only way to know is to make the decision to pull the cylinder.
 

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I have an AntiSplat exhaust air valve with the Napa CRB 229000 valve. There was still enough pressurization that oil was being pushed out the whistle slot in the hose leading to the exhaust air valve.

Off topic, but...

There should not be a whistle slot in the hose between the separator can and the check valve. It's intended to be a vacuum line.
 
Off topic, but...

There should not be a whistle slot in the hose between the separator can and the check valve. It's intended to be a vacuum line.

I believe you run 2 of these valves in lieu of a whistle slot. Perhaps that is a better setup. I don't know. I am mostly interested in preventing blowout of nose seal.
 
I believe you run 2 of these valves in lieu of a whistle slot. Perhaps that is a better setup. I don't know. I am mostly interested in preventing blowout of nose seal.

The check valve at the exhaust tap blocks positive exhaust pressure and opens for negative exhaust pressure, thus lowering case pressure. Case pressure below local pressure has a number of benefits, one of which is that it pulls the front seal inward during normal operation. A whistle slot probably leaks inward as well as outward, and if so, it degrades the case pressure reduction. In comparison, a second check valve only opens when the exhaust tap is blocked.

During abnormal operation (i.e. the broken ring example), two open check valves are probably less restrictive than one open valve and a whistle slot.
.
 

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