I picked up a LS6 long block recently Tried to inspect best I could. All looked good got it home and Cylinder 7 has some scoring. Whats the verdict. I can feel them with fingernail

 

You can clearly see the piston was overheated from detonation at the very top. It needs at the least a piston and rings, clean the cylinder up.

 

I agree Probably detonation, Piston top looks fine just needed a little cleaning. I'll have to check rings and ring lands

 

That piston is TOAST, its the reason the cylinder is scored. Miost likely the top ring is cracked too. If you run it in short order you will have a non functioning number 7 cylinder. Look carefully at the very top edge of the piston ITS MELTED!

 

Thanks, I'll have machine shop look at maybe go with a 3.903 piston set.