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-   -   Strange looking cylinder wall (https://vansairforce.net/community/showthread.php?t=134845)

Kevin Horton 02-21-2016 04:34 PM

Quote:

Originally Posted by Kevin Horton (Post 1055622)
I'll start a new thread about that borescope later today, with more pictures and my detailed thoughts on it.

Here is the thread with my review of this borescope.

BillL 02-21-2016 07:42 PM

Well, the failure is interesting, but only one thing to do - remove and repair.

The area seems much too well defined to be carbon polishing. And too high to be anything but a piston ring. No material transfer for a FOD compression of the top land, and no associated head damage. A guess, is it is likely a broken ring that has finally banged around and turned to scrape the wall. in a most unpleasant way.

Doug 02-21-2016 08:37 PM

Is that a pool of oil?

Kevin Horton 02-22-2016 04:17 AM

Quote:

Originally Posted by Doug (Post 1055827)
Is that a pool of oil?

No, it isn't oil. I should probably have flipped the bottom picture upside down, as you can see the upper spark plug hole near the top of the picture, with the borescope shaft sticking through it. The area that goes up the cylinder wall is well above the low point, so oil wouldn't be sitting there.

edsong 02-22-2016 07:17 AM

Oil
 
Sure looks like oil to me. I had broken rings in a Pitts and it looked exactly like that. It was burning a quart of oil in less than 2 hours.

PeteP 02-22-2016 08:42 AM

Issue
 
Scoring looks to be to high up the cylinder wall to be a wrist pin cap. My guess would be a ring or possibly a FOD. :(

sblack 02-22-2016 09:39 AM

So where is all the aluminum coming from if it is not the wrist pin (which I agree it is not)? The rings are steel as is the cylinder liner. Is the piston coming apart. I guess I could wait for Kevin to pull the jug, but I am just curious and impatient.

lr172 02-22-2016 10:35 AM

Quote:

Originally Posted by sblack (Post 1055953)
So where is all the aluminum coming from if it is not the wrist pin (which I agree it is not)? The rings are steel as is the cylinder liner. Is the piston coming apart. I guess I could wait for Kevin to pull the jug, but I am just curious and impatient.

Assuming a broken ring. The ring piece is likely jammed up on the ring land and creating great pressure against the wall (clearly there is a lot pressure as it has worn steel off the barrel; That pressure also has to be opposed by something), causing all the wear. At some point the land can break or deform and also wear off, creating the AL deposits in the oil.

Larry

KennyM 02-22-2016 02:19 PM

KennyM
 
This is my first post. I own a Cessna 152 & have dreams of building an
RV 8. The post about Lycoming making metal got my attention. I bought
a zero time LC235 got 700 hrs. before it starting making metal. Was
Piston wrist caps ( bad design in my opinion) Can be checked without
Removing cylinder pass rings. Good luck

BillL 02-22-2016 02:32 PM

Quote:

Originally Posted by sblack (Post 1055953)
So where is all the aluminum coming from if it is not the wrist pin (which I agree it is not)? The rings are steel as is the cylinder liner. Is the piston coming apart. I guess I could wait for Kevin to pull the jug, but I am just curious and impatient.

Scott, A piston ring wants to twist in the groove as it moves up and down. A short broken piece has no spring pressure and gas pressure blows it around, as does acceleration forces. It rotates much much more than a complete ring. I have seen them drastically wear the piston groove as they tend to make them selves round. With enough time they will rotate and dig into the piston faster. Combustion gasses blow down in the slot and aggravate everything.

Pretty sure we will see a large distorted ring groove worn in the piston. So - it makes ferrous metal from the wall and aluminum from the piston. It may be causing some skirt erosion as well from debris trapped in between.


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