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02-21-2016, 04:34 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Quote:
Originally Posted by Kevin Horton
I'll start a new thread about that borescope later today, with more pictures and my detailed thoughts on it.
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Here is the thread with my review of this borescope. |
02-21-2016, 07:42 PM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,514
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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.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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02-21-2016, 08:37 PM
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Join Date: Dec 2005
Location: Sydney, Australia
Posts: 427
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Is that a pool of oil?
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Doug Gray
RV-6 completed, flying since July 2010
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02-22-2016, 04:17 AM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Quote:
Originally Posted by Doug
Is that a pool of oil?
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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. |
02-22-2016, 07:17 AM
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Join Date: Dec 2010
Location: Hatton, ND
Posts: 124
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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.
__________________
Edson Grindeland
Hatton, ND
RV-8 Flying
http://www.hattonflyingcircus.com
You do not need a parachute to skydive. You only need a parachute to skydive twice. 
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02-22-2016, 08:42 AM
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Join Date: Jun 2011
Location: Chesapeake, VA
Posts: 219
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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. 
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Pete (AKA Yoda)
Exempt but VAF 2017 Dues Paid anyway 
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02-22-2016, 09:39 AM
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Join Date: Dec 2009
Location: Montreal
Posts: 1,456
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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.
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Scott Black
Old school simple VFR RV 4, O-320, wood prop, MGL iEfis Lite
VAF dues 2020
Instagram @sblack2154
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02-22-2016, 10:35 AM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,277
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Quote:
Originally Posted by sblack
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.
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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
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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02-22-2016, 02:19 PM
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Join Date: May 2015
Location: Baltimore, Md.
Posts: 1
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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
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02-22-2016, 02:32 PM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,514
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Quote:
Originally Posted by sblack
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.
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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.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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