Home » Public Forums » GMCnet » OK an engine question - NOT GMC
| OK an engine question - NOT GMC [message #61243] |
Thu, 22 October 2009 23:43  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I have been putting off fixing my Lycoming 0-320 for almost a year. Tonight I finally got around to pulling #1 cylinder. I had low very compression but I flew it that way always wondering if it was it going to go completely in flight.
Well I pulled the cylinder tonight and found the only top ring broken. Nothing else. No marks on the cylinder walls, no marks on the piston. Valves are good. Nothing but a top ring broken almost perfectly in 1/2.
Now the question is what to do next. I'm leaning toward just replacing the ring (it has 3 - 2 compression and 1 oil) and putting it back together with new O-rings and gaskets of course.
The cylinder is standard and chrome with about 1200 hours on it.
I'm looking for opinions and also any ideas on why it broke. I have never seen this happen before.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: OK an engine question - NOT GMC [message #61253 is a reply to message #61243] |
Fri, 23 October 2009 03:47  |
Craig Lechowicz
Messages: 541
Registered: October 2006
Location: Waterford, MI
Karma: 0
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> Nothing but a top ring broken almost perfectly in 1/2.
Ken,
There are smarter engine people than me on the forum, that will probably chime in, but a couple of thoughts. You didn't say how long it has had an issue, but could it have been cracked (or maybe just over-expanded) on installation? Also, not a lot of compression to start with on airplane engines, but pre-ignition, or a bad backfire (would only take 1 stroke) could do it. (Is this the same one you were having magneto issues with? Rings don't like sparks at unusual times . . .) If there were a lot of wear in the ring groove, that will also cause cracking, but that doesn't sound like the case. Perhaps a bur in the ring groove (now pounded flat?) caused a high stress point. Rings are made from fairly brittle material, so they are sensitive to local stress.
Just a few thoughts. But, if it were me, I would inspect the piston closely, and throw it back together. (Course I can walk without my GMC engine a lot better than I can fly without an airplane engine!)
Craig Lechowicz
'77 Kingsley, Waterford, MI
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| Re: [GMCnet] OK an engine question - NOT GMC [message #61265 is a reply to message #61254] |
Fri, 23 October 2009 08:10 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Gene,
I see you're mechanically challenged like I'm electrically challenged! ;-)
The "lip" at the top of the cylinder is called a "ridge." The tool used to
remove it is called a "ridge reamer."
http://mgaguru.com/mgtech/tools/ts311.htm
The problem is that under the ridge the cylinder is more than likely tapered
and scuffing up the cylinders with a hone won't fix that properly.
When I was in the USAF I had a 1955 Ford with a 292 engine in it. It burned
oil like crazy so I decided to rebuild it. When I tore it down I noted that
it had a serious ridge but I couldn't afford to bore it and buy new pistons
so I ridge reamed and honed it and put oversized rings in it. When it was
all together I hit the starter and nothing happened. I hit it again still
nothing. I hooked up a jumper leads to another battery and hit it again,
this time it turned a bit but no luck. I pulled the starter and had it
checked and it was fine. I decided to just tow it to get it started. When I
released the clutch the engine turned over and started. I ran it up and down
the road in front of the workshop. I later figured it out, the rings were so
tight the starter didn't have enough power to turn the engine over!
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Mr.erf ERFisher
Sent: Friday, 23 October 2009 8:15 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] OK an engine question - NOT GMC
back in the day:
this was almost always caused by a ring grove at the top of the cylinder.
Could be found by mike-ing the cyl, top to bottom. They even made "ring
cutter" tools to remove this lip. then you could hone the cylinder to scuff
it up to seat the new rings.
During a high rev (or something) the top ring would hit the lip at the top
of the cylinder wall and break.
I sure never saw an airplane engine ;>)
gene
> Well I pulled the cylinder tonight and found the only top ring broken.
> Nothing else. No marks on the cylinder walls, no marks on the piston.
> Valves are good. Nothing but a top ring broken almost perfectly in 1/2.
>
>
>
--
Gene Fisher -- 74-23,77PB/ore/ca
"Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: OK an engine question - NOT GMC [message #61270 is a reply to message #61243] |
Fri, 23 October 2009 08:30 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| Ken Burton wrote on Fri, 23 October 2009 00:43 |
I have been putting off fixing my Lycoming 0-320 for almost a year. Tonight I finally got around to pulling #1 cylinder. I had low very compression but I flew it that way always wondering if it was it going to go completely in flight.
Well I pulled the cylinder tonight and found the only top ring broken. Nothing else. No marks on the cylinder walls, no marks on the piston. Valves are good. Nothing but a top ring broken almost perfectly in 1/2.
Now the question is what to do next. I'm leaning toward just replacing the ring (it has 3 - 2 compression and 1 oil) and putting it back together with new O-rings and gaskets of course.
The cylinder is standard and chrome with about 1200 hours on it.
I'm looking for opinions and also any ideas on why it broke. I have never seen this happen before.
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Ken,
In many years of engine durability testing, I have seen more than a few "ring only" failures. I will not say that they are common, but they do happen. A number of those were prototype or special test engines. Of those few that had no damage to the bore, after a very complete inspection of the piston, the broken ring was replaced and the engine was returned to its test cycle.
Your 0-320 (as you stated) is a chrome bore, and it will almost not wear. A check for a top-travel wear step would be smart, but I'll bet you don't have one. I would also check the piston's ring groove side clearance. I'd be willing to bet that it is just fine - too.
If it were my aircraft that I was intending to fly with my wife and her new guitar, I would do the required inspections, reassemble it and fly it. After a couple of hard climbs, my comfort would be restored.
Why don't you hear of failed rings in passcar motors?
Because you are not in the business. It is less common now because of better materials, but up until the recent epoch it was not at all uncommon to encounter an engine that had a sudden increase in oil consumption in the 80kmi region and on inspection there was a broken compression (rings 1 or 2) ring. With VERY few exceptions, passcar motors are parent metal bores and the broken ring will grove the bore and so require at least a hone.
And that is my carefully considered opinion.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: OK an engine question - NOT GMC [message #61295 is a reply to message #61243] |
Fri, 23 October 2009 11:05 |
idrob
Messages: 645
Registered: January 2005
Location: Central Idaho
Karma: 0
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| Ken Burton wrote on Thu, 22 October 2009 21:43 |
I'm looking for opinions and also any ideas on why it broke. I have never seen this happen before.
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Ken: I don't know much at all about engines, but I had an unusual failure on a 5 cylinder 1991 Audi that no one could fully explain. It failed on a long hard 8 mile 7% grade in hot weather, about 100 F outside. Ran fair afterwards, just oil consumption and lower power, a bit rough. I drove it quite some time prior to having it repaired.
When my excellent independent Audi mechanic got it apart, it was a broken or cracked piston. They had never seen it happen before and they do a lot of Audi work. No cylinder bore damage, no other indication of even wear on that cylinder. They just replaced the piston and rings, and put it back together. All is well now.
So, occasionally, stuff just happens, I guess.
Rob Allen
former owner of '76 x-PB
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| Re: OK an engine question - NOT GMC [message #61303 is a reply to message #61243] |
Fri, 23 October 2009 12:48 |
Tin Gerbil
Messages: 236
Registered: October 2006
Location: Vancouver Island, B.C.
Karma: 0
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Senior Member |
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Ken;
We have one (5 hours) rebuilt 0-320 cylinder assembly left over, if you need it. We just zero timed our engine and put 4 new cylinders with 9.5:1 pistons on. Now after 5 hours on the dyno, we find we will have to twist the prop to take advantage of the 170 hp.
A broken top ring can be caused by many things. If you break a ring on installation, it is the top one. With the taper on the bottom of those cylinders, you would have to be awfully haywire to snag a ring on assembly. If the end gap is too tight, it can scuff and break, but you should see some damage to the land. You should also see a line in the cylinder where the gap was. Maybe it was over stressed during installation on the piston? After 1200 hours, I think it is a mystery that will never be solved. The main thing is you are not out $1200 for another cylinder/piston assembly.
We worry about the cost of GMC parts. This 0-320 was $10,185 and mostly for parts. No bunk, shower, fridge, stove or even wheels. I guess as long as I keep loaning my son my GMC, he will be able to afford to keep flying.
Gordon
Gordon
'74 Canyon Lands "Tin Gerbil"
Vancouver Island, B.C.
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| Re: OK an engine question - NOT GMC [message #61311 is a reply to message #61303] |
Fri, 23 October 2009 13:34 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Thanks everyone for your thoughts. I am guessing the ring was over stressed and maybe cracked during installation many years ago.
I might take the cylinder and piston over to the cylinder shop and have them look at. I'll take it to another trusted A&P this afternoon. My favorite IA is currently in Phoenix and I have not been able to find him yet.
To answer the questions.
It is the same engine. This problem appeared long before the magneto problem. I know of no backfire but it could have happened and I just do not remember it since I really do not know when this happened.
The engine ran fine. It was only that I noticed a loss of compression when hand cranking the prop over. I'll check the Mag timing when I put it back together. It was OK a few hours ago when we did the annual inspection.
I need to get this back together quickly and move on to several other pressing projects. I'm going out this afternoon to round up the necessary parts and get some other people to look at it.
Thanks again.
Ken
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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