Howdy new here and impressed with some of the knowledge. This is a KB190 piston from a 360. The motor has done next to no work maybe an hour running time and had spun a bearing. I've had the crank ground and also had the rods resized and have just noticed this? Is it from being knocked around on the way to the machine shop, being roughly handled some where or engine running damage? The engine is less that 10.5 :1 open chamber J heads and was running on methanol with around 36 deg ignition. There are two photo's attached
Cheers
Tony

What do the bearings look like?. I had the same "look" on a few of my pistons when my engine detonated. It also showed up on the main caps and block mating surface. Really shows up in the bearings.

Spun a couple of rod bearings, metal through the engine, lost cam lobes etc. Mains looked OK all things considered.

Detonation will do that, what do the cylinder walls look like in the hole where that piston was? Are the piston skirts good or mark up or tore up?

JMO here but you lost the cam lobes first.. metal
got into the bearings and the piston was just damaged
in the aftermath... a cam doesnt lose the lobes in a
moment it will take a bit of time.. again.. JMO

Bores were OK but I can't go and have a second look 'coz I had the block hot tanked and have sinced honed it. Funny you should ask about the skirts because they were marked up I figured it was trash from the oil so I just cleaned them up with 1200 wet & dry this morning which is when I nboticed this damage?

Been a few years since I've played cars and have never had an issue like this but now I've found all about how they've taken all the stuff we need out of oil. Expensive lesson. How does the oil path go in a Chrysler - Oil pump to lifters then camshaft to crank mains then rods? The rod bearings are way worse than the mains including the back of the bearings? Cam bearing were chopped out as well but they could have been there since 1972 ??

I believe the lobe thrash was falling down on the
rods.. then into the oil, pump, filter, lifter journals,
mains, rods and from the mains to the cam up to the rockers

On Meth with less than 10.5-1 ? I thought that you needed 13+ for Meth ?

Sure looks like foreign object damage to me. When is hard to say now but clean it up and run it

The second pic says that to me also... thats rough looking
on the edge like something was banging on it.. not like
detonation which tends to be smoother(but not always)...
but your right.. a little clean up and run that one again
I've run worse than that one

Meth does like higher pressure.. but we had meth
cars before the E-85 cars with production compression
and they worked fine.. the only thing was the corrosion
so we changed to E-85 instead

What does the upper groove of the ring land look like? Does the piston move freely on the rod? If these two things are OK I'd run it.
Doug

I'm not saying that it has anything to do with the issue but, a hypereutectic piston like that needs extra top ring gap. might want to check that also. I have personally seen guys break that chunk of the piston out.

Might be just barely touching the edge of the chamber in those heads, that is one of the closest points in a J head and unless the chamber is polished it will leave a mark like that where it looks like course sand. That is the area where the piston rocks up and down the most so tight clearance will show up there first.

It don't look like it came from the oily side of the piston, may have got some tiny piece of debris trapped in the for a few revs.