what more than likely caused this

I can't see the picture very well. Did you have the bore machined to work with that piston? Do you know what caused the previous meltdown? What steps led to this picture other than a leak test?
 
The divots and pitting on the top of the piston is a sure sign of foreign debris in the cylinder. I’m thinking a bad lower crankshaft bearing or thrust washer. Got a pic of the crankshaft?
 
pics are still too small to see anything relevant.
after uploading the pic to PB, you need to find the .IMG code for forums, then copy and paste it into your post.
or....
try getting the photobucket app to post full size pics ?
i think the tapatalk app will do it also ?
 
Are those drops of oil, water, or bits of metal? Thrust washer @ bottom of pic looks iffy.

Not a smoking price on the parts, but fair. If it's not a far drive. Maybe talk him down a bit. Unless I don't see them, still need crank bearings.
 
Those are particles and oil so something in the bottom. End is grinding cause I split the case and flushed it before I put on the new parts but I don't know what it is doing it cause those are like gold flakes not silver from the piston
 
I'l bet if you used a feeler gage on the big end of the rod the side clearance is out of spec. To me the thrust brg looks wavy and discolored. That is probably where the "gold" flakes came from.
 
Those are particles and oil so something in the bottom. End is grinding cause I split the case and flushed it before I put on the new parts but I don't know what it is doing it cause those are like gold flakes not silver from the piston

What was the reason for splitting and flushing?

Did you have a piston explode?

Splitting and flushing is really not quite enough, all the bearings must either be replaced or be removed and thouroghly cleaned to remove all debris.

I always advocate replacement of bearings.
 
I'm pretty sure it had water in it from the last owner cause when I split the case it smelled like rotten eggs the reason I split it is to get all the particles out from the last time it destroyed the piston gonna split the case today and completely co through everything and replace it its not rust though but we will see I think I'm gonna try to save some money and send it to Ken o Connor so I know its done right
 
I'm pretty sure it had water in it from the last owner cause when I split the case it smelled like rotten eggs the reason I split it is to get all the particles out from the last time it destroyed the piston gonna split the case today and completely co through everything and replace it its not rust though but we will see I think I'm gonna try to save some money and send it to Ken o Connor so I know its done right
Sounds like good idea....