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03-01-2016, 09:34 PM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,297
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Quote:
Originally Posted by BillL
Kevin, You might be able to look at the cam with your scope. Note there are some particles embedded in the skirt, and the top ring face looks rough. It is hard to tell in that photo. If the ring face disintegrated (root cause), it could cause the flakes, and then the blow-by overheated the ring (and top land) and froze the ring. Skirt FOD elevated the aluminum.
It seems too much a coincidence that you shed cam flakes at the same time as a ring failure.
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I agree with Bill. If the ring is firmly stuck your metal could be from the ring. Assuming you have a hardened barrel, that metal will be harder than the steel ring. Once you wear past the chrome layer, the ring will give up more metal to wear than the wall. Also, don't discount how much metal material that .001" represents. It is a fairly wide area.
Given the wide area of .001 area, clearly there is a lot of pressure here. Remember, each time you bring the engine up to full temp, that AL piston is growing faster in size than the barrel and this is likely when the wear is occurring. I would examine the ring closely. If the Chrome is worn off, I would speculate that the ring has been making metal in your filter. Be sure to mark the area of the ring adjacent to the wear area before removiing. You can then mic the ring in that area and compare to others to see how much wear there has been.
Crank issues highly unlikely. You'll see bronze material long before steel. Lifters are certainly a possibility, but seems a big coincidence if the cylinder wear is new. If you recently saw a rise in oil consumption that would indicate the cylinder wear is new. However, what you have here shouldn't create a significant reduction in power and may have been there for a while.
Good luck and let us know what you find.
Larry
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N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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03-02-2016, 04:45 AM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Thanks for the advice guys. I'll get back out to the hangar this weekend to take a closer look at the valve train and pull the piston pin so I can bring it home for a closer inspection.
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03-04-2016, 04:23 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Today was warmer than the past few days, and I had a slow afternoon at work, so I took some time off and headed to the hangar. I warmed the wrist pin bosses in the piston with a heat gun, then managed to push out the wrist pin with a piece of wooden dowel. Then I stuck my borescope inside and took a look.
The #4 intake tappet looks pretty ugly. Drat. I managed to get the tip of a finger on the tappet by rotating the crank a bit, and it feels slightly rough, which confirms the borescope image.
I won't print what I said. I've been resigned to finding valve train issues since I first found metal in the oil, but I had been holding out hope that there was a cheaper explanation. At least now I know what the issue is, and what I need to do to get it sorted out.
I'll start pulling the engine on Sunday, and then figure out where I will send it. This is the second time in 3 years with cam or tappet issues, so I'll get the roller lifter mod done this time.
Time to get drink wine. Lots of wine.
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03-04-2016, 05:21 PM
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Join Date: Apr 2008
Location: Central Iowa
Posts: 317
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Question /educate me...
When this sort of trouble starts, does the erosion start in the center and make a "dent or low spot" which then causes more erosion of the surface toward the outer perimeter!
My first thought when looking at the photo was "that seems really close to the edges, how does that erosion of the surface get that close to the edge?"
Kevin, thanks for the thread, sorry for your trouble.
Jim
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RV-6
RV-10 tail kit 50%
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03-04-2016, 06:48 PM
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Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,218
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Kevin, any theories on the underlying cause of the valvetrain issues? Do you think the overspeed incident caused the followers to hammer on the cam, or is something else at work here?
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Kyle Boatright
Marietta, GA
2001 RV-6 N46KB
2019(?) RV-10
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03-04-2016, 07:45 PM
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Join Date: Jun 2012
Location: Frederick, MD
Posts: 821
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Quote:
Originally Posted by Jimd
When this sort of trouble starts, does the erosion start in the center and make a "dent or low spot" which then causes more erosion of the surface toward the outer perimeter!
My first thought when looking at the photo was "that seems really close to the edges, how does that erosion of the surface get that close to the edge?"
Kevin, thanks for the thread, sorry for your trouble.
Jim
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The cam follower rotates in operation to spread wear over the surface. As the center wears the wear extends closer to the edges. Looks like typical spauling.
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Dan Morris
Frederick, MD
PA28-140
Hph 304CZ
RV6 built and sold
N199EC RV6A flying
Learn the facts. "Democracy dies in darkness"
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03-04-2016, 09:26 PM
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Join Date: Dec 2009
Location: Montreal
Posts: 1,456
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As much as this sucks, it was found on the ground before it became a safety problem. If anyone ever needed a reason to cut open their filter here it is.
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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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03-04-2016, 11:00 PM
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Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,573
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two separate issues?
so at this point, do we think that the piston ring/cylinder wall issue and the cam follower spawling issue are completely separate and unrelated? Did debris from one source precipitate the other problem?
I have a hard time imagining that this traces back to the overspeed. Folks run these engines at much higher revs than you saw continuously in racing.
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Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 625
LS6-15/18W sailplane SOLD
bought my old LS6-A back!! 
VAF donation Jan 2020
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03-05-2016, 06:03 AM
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VAF Moderator / Line Boy
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,256
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Wow Kevein - ugly isn't a strong enough word for that tappet face! Even the "ridiculously beat up" examples at Lycoming school didn't look that bad.
Is this a first-run engine, or was it built up as an overhaul? If its first run, there has been something going on in there that wasn't right in the first place.
Paul
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Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
http://Ironflight.com
Last edited by Ironflight : 03-05-2016 at 07:26 AM.
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03-05-2016, 06:12 AM
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Join Date: Feb 2005
Location: Chesterfield, Missouri
Posts: 4,514
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The image makes one wonder if it is a lubrication problem. Sure looks awful. Glad it did not fail in flight and wreck your airplane.
I am a wimp when it comes to engines...and needlessly spend money to offset the wimpiness by calling Barrett Precision in Tulsa and order a new one. Done it twice and never looked back.
That's one reason I am slowly going broke but the motor up front sure runs well.
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