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I own a 2016 Chevrolet Caprice PPV, 6L L77. I recently had a lifter failure on a AFM/DOD cylinder. Immediately turned the car off as I recognized the problem. Upon disassembly I found that the camshaft had not been destroyed. The lifter was not marred or damaged, no scoring or pieces missing. I cut the oil filter open found no forbidden glitter of any kind. I dropped the oil pan, also no glitter or debris of any kind. All push rods were good. No scoring or damage to the ends.
As I was cleaning up the motor to prepare for reassembly, specifically the tops of the Pistons and block deck, I noticed minor scoring on the bottom of the piston that corresponded to the bad lifter. I examined the head and found similar minor scoring on the cylinder head for that cylinder. See photos.
My question. As I have found no debris, I have no heavily damaged parts, No missing material from lifters, pushrods or spark plugs. What could have caused this damage? If something was in the cylinder, why did it leave such little damage? Why is the damage in a very specific spot on the piston and cylinder head? Wouldn't the debris have bounced all over the cylinder? Also, wouldn't an engine turning at 2500 RPM eat itself up if something had been in the cylinder? What am I missing?
Honestly, that almost looks more like light valve contact than debris damage. If the AFM lifter stuck momentarily , the valve may have just barely kissed the piston a few times in the same spot before shutdown, which would explain the marks
"Light valve contact" wouldn't pepper the deck surface of the head with matching marks, or the piston in a space nowhere near any valves. That can be ruled out.
Detonation doesn't leave long narrow peck marks in the head surface with rolled-over edges onto other surfaces. It leaves pits, almost like the metal has been boiled or something. I think that can also be ruled out.
Looks to me like something got into that cyl at some point and took a beating, and now it's gone. Probably totally unrelated to the lifter failure since there's no way that lifter pieces can end up in a cyl without leaving any other evidence anywhere. Might have been something left during its original build that got stuck in the ring land, or maybe on the spark plug when the plug got changed, like a little piece of wire or something, and it did what it did, broke loose, and got expelled.
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I need an opinion... 
