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  #1  
Old 02-20-2016, 05:37 PM
Kevin Horton's Avatar
Kevin Horton Kevin Horton is offline
 
Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,365
Default Strange looking cylinder wall

The IO-360-A1B6 engine in our RV-8 has been making some metal. I first noted it when inspecting the oil filter after an oil change in August - I found roughly 50 shiny, ferrous flakes. I consulted Lycoming SI1492D, which describes various types and amounts of metal one might find in an oil filter, and recommends action. Based on that recommendation, and after consulting with three Aircraft Maintenance Engineers (an AME is the Canadian equivalent to an FAA A&P), I flew the aircraft for two hours and checked the filter again. I counted 7 flakes, so I flew 10 more hours (I was away for most of the rest of the year, so this took until January). This time I found the rate of making metal had gone up quite a bit, and now I was seeing what looked like alumimum along with the steel, so I grounded the aircraft.

When I first found the engine was making metal, I feared it could be the cam. After finding aluminum too, I did some research, which lead me to wonder if it could be a broken piston ring.

I acquired a Vividia VA-400 borescope, and today I took a look in the cylinders. Three cylinder looked pretty good, but #4 has a very strange, wide area where the cross hatching is not visible. This area goes all the way up the cylinder. At first I thought it might be a piston pin issue, but I'm pretty sure it is no where near the front or back of the cylinder (you can see the top plug hole, with borescope shaft through it, in the second photo). The next step is to find an AME to help me pull that cylinder to investigate.





Has anyone seen anything like this before?
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  #2  
Old 02-20-2016, 05:59 PM
aerhed aerhed is offline
 
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Default

It goes beyond the top of the ring travel. I think you're going to find a piston problem at least.
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  #3  
Old 02-20-2016, 06:01 PM
aerhed aerhed is offline
 
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Looking again I see I was fooled by the ring step, so something in the top ring.
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  #4  
Old 02-20-2016, 07:29 PM
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Mike D Mike D is offline
 
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Default

I had the same issue. It turned out to be the cap that covers the wristpin was rubbing in the side of the cylinder. This caused scoring on the cylinder wall and the. On the rings. My best guess was it was caused by oil sludge that baked into a hard ring and kept the cap from floating like it should. This pushed the cap into the side wall if the cylinder.

What is odd about yours is that is in the wrong position to be the cap.

My compressions were below acceptable and I had to change the cylinder and piston assembly.
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  #5  
Old 02-20-2016, 11:18 PM
lr172 lr172 is offline
 
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Default

I have seen similar in auto engines. Cause was ingestion of debris, but they were narrower than yours. I believe something is amiss in the top ring area. Hard to say if it is a broken ring, maybe ring land damage, maybe debris. It likely first wore the cylinder wall smooth, but the appearance of aluminum in the oil would point to the piston now wearing. the clocking of the wear pattern excludes a piston pin issue.

You definately need to pull the cylinder and investigate. You might still be able to hone it depending upon how much metal it has removed. You can also bore it out, as you will likely need a new piston given the appearance of AL material in the oil.

I am curious to see what the cause is.

Larry
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  #6  
Old 02-20-2016, 11:49 PM
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bhester bhester is offline
 
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Default Borescope?

Quote:
Originally Posted by Kevin Horton View Post
I acquired a Vividia VA-400 borescope, and today I took a look in the cylinders.
Kevin, sorry to hear about your cylinder problem. I looked at that link for the scope, looks like a good tool to have, better than those dental cameras.

Can you give us more input about it? How do like it? I'm about to order one.
Thanks!
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  #7  
Old 02-21-2016, 06:02 AM
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Kevin Horton Kevin Horton is offline
 
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Quote:
Originally Posted by bhester View Post
Kevin, sorry to hear about your cylinder problem. I looked at that link for the scope, looks like a good tool to have, better than those dental cameras.

Can you give us more input about it? How do like it? I'm about to order one.
Thanks!
I'll start a new thread about that borescope later today, with more pictures and my detailed thoughts on it.
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Last edited by Kevin Horton : 02-21-2016 at 06:12 AM.
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  #8  
Old 02-21-2016, 08:46 AM
Robert Anglin Robert Anglin is offline
 
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Location: houston, texas
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Default Picture purfect

It is hard to tell from a couple of pictures, but you are doing the right thing here by removing the jug and looking at the rings and wrist pin ends. If it were a wrist pin plug the wear would be in line with the front or back of the cylinder just like the line between the spinner to the tail and would be the diameter of the pin. I think this scarring is a little wider than the pin cap would be, but it is hard to tell from the JPG. Looking at the wear on the cylinder up from the bottom it looks like the top compression ring is going up a little higher than the scar goes. this would lead me to think it would be at the second ring or the oil wiper ring. Again it is hard to tell from the picture, but you will find it when you pull the jug. Just a guess in the dark, but I would suspect a broken or wedged ring or ring grove, it does happen. You will be fine with a jug transplant. Good luck, Yours, R.E.A. III #80888
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  #9  
Old 02-21-2016, 09:24 AM
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Caveman Caveman is offline
 
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Default Finger strainer check

Hi Kevin,

Just curious if you checked the oil sump finger strainer and if so what you found there. Depending on the size of the metal flakes you might find more material there.

Joe
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  #10  
Old 02-21-2016, 02:40 PM
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Kevin Horton Kevin Horton is offline
 
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Quote:
Originally Posted by Caveman View Post
Hi Kevin,

Just curious if you checked the oil sump finger strainer and if so what you found there. Depending on the size of the metal flakes you might find more material there.
I did check the oil sump finger strainer when I changed the oil (i.e. the oil change where I first found metal), and it was completely clean. I haven't looked at it since, as I haven't drained the oil when changing the oil filters for inspection.
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