Yesterday I posted a question about a '94 Dodge Intrepid with something (I must have dropped it in myself when working on the intake manifold before) stuck in one of the cylinders. I mentioned that I’d spoken to a few mechanics about a replacement and they’d said $2100-$6000. Today I pulled the head off and saw that the top of the piston was pretty beat up and the head around the valves was pretty beat up too. The valves didn’t look beat up at all. The mystery part was that I didn’t find anything in the cylinder to indicate what was banging around. I expected to find a washer or a nut or a small screw or something. Perhaps it beat itself to small pieces and I fished all of the pieces out with a magnet earlier? Is there somewhere else it could have gone? The piston is right now at the bottom of its cycle. The walls of the cylinder seem pretty good. So, my question is this: what do I do? What’s the worst thing that could happen by cleaning it all out and putting it all back together? Could my expected washer be hiding somewhere? How much could a machine shop do for my head? I should not here that the car has never been driven with this problem, but it has been run. Thanks, JD
Whatever got mashed up I’m sure was partly ejected through the exhaust. I’d inspect the valves carefully and rotate them open to check for any bends or damage and make sure they seat properly. If the valves are good and the cylinder wall is in decent shape you lucked out. Put it all back together with care and by the book and drive it. Worst thing that happens is it makes some noise really. If you didn’t bend a rod or spin a bearing and there’s no real damage you’re good to go. Just watch where all those bolts and washers go this time 
Now, you have to get the piston out and replace it. New ones used to cost about $16 each for an ordinary Chevy 350 engine. You may notice that the top ring is jammed. Make sure the connecting rod swings all the way and touches the piston. If it doesn’t, it may have to go too. Do it to all four because you want to find out what’s knocking. If the rods don’t swing freely, it is causing piston slap. If they rattle, it’s an even worse problem. I forgot, if the wrist pin won’t come out with a 10 ton press, throw the rod and piston away.
Whatever is was could have disentegrated with heat by now or been blown out past the exhaust valve where is is not caught in the catalytic converter.
It can be run like this but there is one thing you MUST do. You need to take a Dremel tool, carbide burr, or whatever and round off any sharp edges on any of the nicks or gouges on the piston top and cylinder head. Get them as smooth and rounded as possible.
If you allow the sharp edges to remain they will more than likely glow red hot when the engine is running and cause a severe detonation problem.