Proper alignment of cams to crankshaft timing marks.
Evidence of chain contacting anything else besides it's normal gears and tensioner/s.
Drain oil and strain, looking for particulate contamination, metals, chain guide material, etc...stuff that could plug the oil screen.
I believe the interference is at the outer edge of the pistons, if so, damaged/pinched ring lands @ the piston outer edges if you remove the head.
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