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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.
The car is almost back together. Fingers crossed 🤞
The gentleman that tunes the car believed it to be detonation. The machine shop who milled the heads on the car didn't think it was detonation, he believed something got into the cylinder. Neither one of them thought it was a major cause for concern. That being said, I am still mystified how debris can get into a cylinder and stay in 10% of the overall cylinder/piston area and NOT bounce all over the place. Since the affected area is only the "squish" zone and not near where the valves are that rules valve contact out. It also seems like a very big coincidence to me that the only cylinder that has such damage is the cylinder that suffered lifter failure. Either way, I appreciate everyone that chimed in with suggestions. Thank y'all very much
To me, that looks like detonation. If something had gotten in there and bounced around, you would have random marks all over the place. The cyl walls look a little beaten on, but it is what is. I would have the heads touched min to clean up the detonation marks and put it back together. The tune is suspect and I would watch oil consumption and run a catch can to minimize any detonation going forward. I would def have the tuner back it off some once you get it back together.
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I need an opinion... 
