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Lycoming Piston Pin Plug Failure

N

N208ET

Well Known Member
http://imageshack.us/a/img538/8093/DVYSbA.jpg[/IMG]http://imageshack.us/a/img537/2203/cEBvKg.jpg[/IMG]
Anybody see anything like this happen before? It had the bronze plug installed which wore itself to pieces, taking out the piston with it. Cylinders are chrome, heck it might be serviceable still. The engine however had to come off for complete tear down. Metal was in the bearings and throughout the case. The sump was full of metal specs. Total Buzzkill!
This is a Lycoming 0-360 narrow deck engine. EMag, Catto Prop, and have used auto gas the last 150 hours or so. TT 500 hrs on lower end, 700 hours on cylinders.

Randy
8A
 
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That is some ugliness for sure. On the IO360-C1C on our Arrow, with 500 since a top, we had some metal show up in the oil filter and oil analysis.

Thought at first the excessive wear on some of our pin caps was the source:

piston2caps---Copy.jpg


But, when the last cylinder was pulled, a failed ring and chunk of piston was probably the culprit:

piston4bottom.jpg


Luckily we had an overhaul fund, so the decision to do the right thing was pretty easy.
 
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Broken Ring

It looks like it started with a broken ring. Without seeing the top of the piston it is impossible to tell if that was caused by detonation or from the initial build process.

Are you checking cylinder leak down annually and oil filter inspection for metal on each oil change? That ring has been broken for a long time. Hundreds of hours, not tens of hours.

Edit: Shaving off the pin end button is typical. Usually, it is due to it passing over a step in the cylinder bore caused by the ring travel area. Conti uses a piston ring at the bottom of the piston so that the button won't pass by the step from ring wear! A twisted, but effective design, solution. Usually, it just shows up as metal in the screen and filter. It is identified by the sliver shape of the metal pieces. They also have aluminum buttons (lighter). The button was NOT root cause.
 
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2 Cents

If this were mine. I would not use that Rod again. I would exchange it for one you knew was good and had the rest-pin bushing boarded strait and reamed very nice. Just me and my picky ways. Yours R.E.A. III #80888
 
Bill, just to clarify, those pics I posted were from the Arrow, not Randy's RV. We did a leak down test every 100 hours, nothing notable.
Oil analysis and filter check every oil change. We had a spike in the analysis with no metal found on one oil change, then a continued spike
with fine particles in the filter on the subsequent oil change. That led to the pulling of cylinders, and eventual overhaul.

Sorry for the threadjack, Randy.
 
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N208ET said:
http://imageshack.us/a/img538/8093/DVYSbA.jpg[/IMG]http://imageshack.us/a/img537/2203/cEBvKg.jpg[/IMG]
Anybody see anything like this happen before? It had the bronze plug installed which wore itself to pieces, taking out the piston with it. Cylinders are chrome, heck it might be serviceable still. The engine however had to come off for complete tear down. Metal was in the bearings and throughout the case. The sump was full of metal specs. Total Buzzkill!
This is a Lycoming 0-360 narrow deck engine. EMag, Catto Prop, and have used auto gas the last 150 hours or so. TT 500 hrs on lower end, 700 hours on cylinders.

Randy
8A
Click to expand...

YES!

Was flying with a friend in a Tri Pacer a few years back, he flew me to and from Jeff City, MO for a RV-6 check out.

On the way home, the engine did not seem to be producing the same power as earlier that day. We made a precautionary landing at Herman, MO checked things over visually and found nothing amiss. Cranked up, good mag check, and continued on to Spirit.

Next day the same thing was found, the wrist pin retainer had failed and the pin was destroying the cylinder - big time.

It is a credit to the toughness of a Lycoming engine. We made it home. :)
 
It looks like detonation erosion on the piston crown edge, did the compression rings have any tension left in them, looks like they were not sealing for a long time, only takes a small amt of oil ontop the piston to precurse detonation......those are some scary pics!
 
Oh NO Randy!! That is not fun at all!! Sorry to see the damage there.

What made you tear it down? Was it a sudden symptom or gradual?



Richard from Duckworks and Langaire
 
Chromed cylinders

I also have chromed cylinders. Was wondering if chrome lining wears out rings faster than standard cylinders? John
 
catmandu said:
Bill, just to clarify, those pics I posted were from the Arrow, not Randy's RV. We did a leak down test every 100 hours, nothing notable.
Oil analysis and filter check every oil change. We had a spike in the analysis with no metal found on one oil change, then a continued spike
with fine particles in the filter on the subsequent oil change. That led to the pulling of cylinders, and eventual overhaul.

Sorry for the threadjack, Randy.
Click to expand...

Thanks for the clarification - I should have checked the links, I assumed you reposted his links.

So - to the real pictures - yes it appears a pin button failure - odd though that it wore so much it fell out, the Conti ones have a longer section within the pin. Some careful investigation is in order.

Bret, I am not seeing any evidence of detonation - where did you see it? The one area that looked like aluminum was added material not eroded. Usually, the edge of the piston is broken, sometimes rounded off (eroded), and the carbon deposits are cleaned off from the "impact". This kind of erosion can happen on diesels too, and the piston will look like the craggy peaks of the Patagonia range. The valleys can be 1/8" deep.

edit: I meant to respond to Bret's comment, I don't know where Andy came from.
 
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The outer edges of the piston ring lands between the rings show that the rings were not sealing, they should be as clean as the skirt. did you take the rings and square up in the cylinder and check end gap and ring tension, if all tension is gone, the rings have seen a lot of heat. Also if too small a ring gap was installed originaly they could butt under excessive heat and break things.....
 
Oh it didn't fall out

There were bits and pieces of it left in the piston socket, and in the piston pin itself. What wasn't there was in the engine with the debris from the piston and a little from the rings that were broke. Most of the rings were still on the piston, the top ring was still intact. I had about 25 hours since the last oil change and didn't notice anything when I cut the filter. I ended up having a low oil pressure alarm on rollout when I landed at my home airport. (lucky) The first spark plug I pulled was black and wet, the bad cylinder. I pulled the rest and the looked fine, then did a compression test and got 0 on that one. Pulling the valve cover and finding metal and things have gotten worse the further I went. I do believe the crankshaft is serviceable, but I haven't had it magnafluxed yet. at least I'm learning lots!
 
Bret

It looks to me that the oil ring let go after the damage got that far, then the secondary ring got wore off. This left only the top ring to do the work and started letting chamber activity go by and progress down the piston while oil was being pulled into the cylinder, causing things to get black and moist appearing. I had oil in the intake tube when I took it off. The oil consumption hadn't really changed that I could tell lately, leading me to believe the engine didn't run a extremely long time like this, but who knows. And no, I didn't measure anything out, I'm away for work now so can't do anything but theorize for now.
 
I don't see any evidence of detonation here. Broken ring lands are usually the first manifestation of detonation in about 95% of cases.
 
Pins

This problem goes back to at least 1994. Do a google search using "Lycoming piston pin plug problems" and you will find a LOT of information.
One opinion is that if the lower piston ring wears a visible step at the bottom of the pistons travel, that this step will shave off a tiny bit of metal from the plug over time.
There have been three different plugs used in recent years, the first generation MUST be replaced. I didn't find an AD, so probably lots of engines flying with the original plugs.
Some shops have been eliminating the plugs and installing circlips on experimental engines.
 
jrs14855 said:
This problem goes back to at least 1994. Do a google search using "Lycoming piston pin plug problems" and you will find a LOT of information.
One opinion is that if the lower piston ring wears a visible step at the bottom of the pistons travel, that this step will shave off a tiny bit of metal from the plug over time.
There have been three different plugs used in recent years, the first generation MUST be replaced. I didn't find an AD, so probably lots of engines flying with the original plugs.
Some shops have been eliminating the plugs and installing circlips on experimental engines.
Click to expand...

Hey Jim,
Yes, this is not new (for Lyc) , and as long as there is a wear step to be crossed by a pin, it will still shave off material - but. . . I thought this plug was pressed in the end of the wrist pin. Are they not pressed in? What is the progression of failure to result in an erosion in the pinbore like this one? As opposed to just a stream of shavings contaminating the engine?

BTW - I have mentioned before -Conti added a piston ring at the bottom of the piston skirt to lower the ring step so the pin does not cross a ridge. That is the only reason for that ring down there. Also - I was told years ago that circlips would not stay in, thus the reason for the centering plugs.
 
Pins

I think the first generation was pressed in, #2-all aluminum plugs, and #3 aluminum bronze and shaped very differently and do not engage the piston pin.
The google search will lead you to the Lyc service instruction and drawings of the plugs. Apparently Lycon has had good success with the circlips. There was an article on this and other Lycon features about a year ago in Kitplanes. I don't agree with some of what Lycon does but the circlips seem like a better solution than the plugs. One suggestion is that the circlip problems have been in motorcycles which turn extremely high r/m's.
There are also discussions of Teflon plugs instead of the aluminum/bronze.
Another issue is assembly lubricants. Lycoming calls for a special lubricant on the plugs.
I was not able to find a source of ANY of the special lubricants in the Lycoming S I. I called Lycoming and they would not tell me anything. Their standard answer is "contact your maintenance provider"---which would be me!!!!
A totally incompetent company which should have gone out of business 40 years ago, but they have a captive audience.
 
Piston Pin Plug Failure

I have seen many many Lycoming piston pin plug failures. I have not seen any quite that bad. I have seen the plug wallow around in the cavity in the piston until it was small enough to go inside the pin. That let the pin move side ways enough to get into the cylinder wall and ruin the cylinder.

Because this has been such an ongoing problem Superior and ECI both carry/developed Lycoming piston pins with swagged in integral plugs, much like some of the Continentals use. I would never assemble a Lycoming with the old style separated pin plugs!
 
Plugs

The best way to address this would be to take a survey of several of the top engine builders and find what they are currently using.
I have several thousand hours in Lycoming powered airplanes and have never personally had an engine failure. Two mag failures but the engine did not stop running.
 
Piston Pin Plug Failure

I had this EXACT same thing happen to me some years ago when I owned a Mooney with a Lyc. O-360 A1D. It was discovered when the governor quit working because a chunk of metal was lodged in the gears. The oil filter was crammed full and iron filings from the rings had spread throughout the engine. A complete (and unplanned) overhaul was required.

The engine had chrome cylinders. I do not believe it was caused by leaking or broken rings. I think it is inherently a Lycoming design flaw, brought on by the plug either being slightly misfitted, or lack of lubrication at startup perhaps due to a period of inactivity. Some rust on the cylinder wall might also cause it but in my case this was not possible because of the chrome.

Back then there was a publication called "Light Plane Maintenance." I wrote to the editor and he told me that this type incident was not uncommon.
 
I often used Teflon pin buttons in race engines and never saw a failure. The material is rated for up to 500F. I built a turbo street Toyota engine with Corvair forged pistons. I machined some Teflon pin buttons for it. This engine went through 3 owners over 14 years and had 4000+ hours on it before it went to the crusher. The bottom end was never touched in that time.

These are commonly fitted to VW performance/ race engines. Anyone using such things in Lycomings?
 
I'm not sure how you could install these wrong

Short of putting the plug in backwards, and if you do that I doubt the piston would slide into the cylinder. Lack of lube is a possibility, I guess. Who knows, I am going to investigate better designs and hopefully come up with something else.
 
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