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  #1  
Old 11-27-2021, 10:46 PM
gasman gasman is offline
 
Join Date: Mar 2007
Location: Sonoma County
Posts: 4,196
Default Loss Of Oil Pressure caused by a broken ring

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?
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  #2  
Old 11-28-2021, 12:21 AM
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Mike S Mike S is offline
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Broken ring can cause increased crankcase pressure that forces oil out the vent ---maybe even blow out the front seal.
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  #3  
Old 11-28-2021, 12:35 AM
JDeanda JDeanda is offline
 
Join Date: Apr 2013
Location: Ventura, CA
Posts: 291
Default 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.
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  #4  
Old 11-28-2021, 07:32 AM
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Walt Walt is offline
 
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Excessive crank case pressure can push out a front main seal which will lead to rapid oil loss.
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  #5  
Old 11-28-2021, 07:46 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Quote:
Originally Posted by BillL View Post
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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Last edited by lr172 : 11-28-2021 at 07:49 AM.
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  #6  
Old 11-28-2021, 08:27 AM
Frank Smidler Frank Smidler is offline
 
Join Date: Feb 2005
Location: Stoughton, WI
Posts: 494
Default 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.
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  #7  
Old 11-28-2021, 08:48 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Frank Smidler View Post
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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Last edited by lr172 : 11-28-2021 at 09:16 AM.
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  #8  
Old 11-28-2021, 12:12 PM
OKAV8r OKAV8r is offline
 
Join Date: Feb 2007
Location: Seattle
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Poor technique installing the rings on the piston could increase the potential for ring failure, also
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  #9  
Old 11-28-2021, 04:30 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,381
Default Key Event - thanks for sharing

Quote:
Originally Posted by Frank Smidler View Post
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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Last edited by BillL : 11-29-2021 at 06:59 AM.
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  #10  
Old 11-28-2021, 05:52 PM
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rocketbob rocketbob is offline
 
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Quote:
Originally Posted by Walt View Post
Excessive crank case pressure can push out a front main seal which will lead to rapid oil loss.
Last year I "added" a front main seal on a RV-6 that didn't have one. Flew like that for years.
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