yea people don't realize just how strong forged pistons are, so a little scuffing on one section of the piston, as long as it doesn't affect the shape and dimensions of the piston, is perfectly reusable. Hell the scuffing on my skirts took me 5 minutes to polish out with a green scotch brite pad

I have a built VG30DETT that I'm freshening up/doing more work to and the pistons came out with the tops stained with carbon and fuel... Working my magic with green scotch brite, 1000,2000, and 3000 grit sand paper, plus a de-burring tool and some amazing metal polish they all came out perfectly clean, not a single scratch or blemish

If I posted pics of them you would swear they are new lol. I can do some pretty awesome things with metal (machine shop wisdom)

 

Those pistons are pretty janky. The head contact and heat damage may have compromised the top ring groove. Between that and the skirt wear those have got to be all different shapes and sizes.

Lots of guys around that can talk a good game and screw parts together. Doesn't mean it's going to be any good if the basics are missed. I have seen way too many "built" engines that are passed in strength and reliability by a stock motor lol.

 

it makes me wonder what happened to make those pistons so out of whack... I don't think a single part of the piston is still round

 

isn't it obvious? contact with the head is the biggest contributor. 2nd contributor would be ring end gaps not set correctly (actually not even set at all, they are completely untouched)

 

the piston to wall was too tight. cp's are notorious for needed a bit extra ptw

 

Normally contact with the head will just squish the quench pads on both the head and piston, never really does and catastrophic damage unless valves were open when it happened. Ring end gaps would really just cause the motor to run like ****, wouldn't have much to do with any structural deformation of the piston in any area.
That's what Im thinking as well... The tight p2w resulted in continuous contact with the cylinder walls and when the piston "rocked" on each stroke it deformed the piston skirts and other areas, then when it hit the head it deformed the quench pads and possibly the valve reliefs

 

Looks like it was built really tight, but the engine was actually running hot and created the chain of events.

Honestly, with myself running a tuning shop full time right beside an engine builder, I've seen too many variations of different failures. It's still always a guessing game because what we see now is just a snapshot of a brief period the engine was running in.

It is very similar to reading spark plugs; unless the engine was literally on the dyno with full throttle runs and only within minutes of the failure, we get a mix of regular driving (say if the car runs rich all the time), but runs lean under boost, etc... It's often difficult to determine what really happened first. Bad tune, poor cooling, etc... limits change when the engine is hot so it could be a perfect tune for 190 deg F, but then too much to handle at 220F, for example.