Replacing a melted piston.
 

Hi y'all. I'm gonna need some help here if you guys don't mind. I have a 79 k20 350. I bought it in NM and it sounded like it was running on 6cyls. I replaced the distributor, cap, coil. Nothing helped. I Was on the highyway and it suddenly overheated. I got it home cuz the motor was acting like it was seized up. Put roughly 1.5 oz of marvel mystery oil in all the cylinders and let it sit for a week. It turned over by hand at the flywheel with a crowbar. So i bumped it with the starter. Coolant came out of the #5 cyl spark plug hole after 2 bumps. Turns out the starter was getting stuck in the engaged positon after 3 cranks. So forced it to free itself and bumped it until it turned over all 8cyls. #8 cyl had coolant come out the cyl also. I removed the heads, it had the original Steel head gaskets. The gaskets weren't physically "blown" per say. But the #5 piston was melted. I'm needing to get it up and running on the cheap, so we can have 2 running vehicles. Can i just replace the piston with a stock piston, rings & bearings, & new head gaskets?https://cimg0.ibsrv.net/gimg/www.per...df9612652b.jpg

Is the cylinder wall okay and not scratched and marked up? No visible cracks?

Also that piston doesn't melted, it broke a ring land off and it did a little bouncing around in there.

But otherwise yeah you could just buy a new piston and slap it back together if you wanted too, 350's are like lego's.

The walls are smooth for the most part. Just the top and the part of the cylinder where it " melted" had a build up of metal. It appears as though i could hone it out. The top of the cylinder had a 1" wide by 3/8" deep chunk of metal that came out by just lifting it up with my fingernail. But I'm still confused on why the #8 cylinder would have coolant in it?

Looking at the cylinder to the right, at the bottom of the pic, it looks like that ring land is about to break as well.

It's definitely chewed up.

Just swap a 5.3 in it and call it a day.

It has a 5.7 in it right now. I'm still not sure why there is coolant in the cylinders as the head gaskets weren't clearly "blown". I checked the heads and didn't see any visible cracks. But they are 624 heads. Going to get a set of 993 heads. Swapping for 2 old carbs.

When you pulled the heads off, likely coolant got into the cylinder that way.

Before i removed the heads i removed the spark plugs and turned the motor over by hand and coolant came out of the spark plug holes. I knew then there was a problem.

Block could possibly be cracked but I doubt that. Once you pull the pistons out, it'd be worth a look.

kinda late here to the party but are all the pistons in the correct orientation? Notice the marking on the tops the last 2 are one direction? Just a thought

The engine is stock and has never had the heads off before. It still had the factory steel head gasket.