I bought this ls2 from someone that had 27k miles from a rolled ss trailblazer. He said he had started the engine in the tbss and it ran perfect. When he put it in his car the shop told him there was some tapping. They thought it may have been a lifter and pulled the heads. I dont know how to post pictures, but the edge of one piston is missing carbon it's a spot about and inch long and a 1/4 inch wide. There was no damage or even signs that the piston was hitting the head. I also have shown the piston to a few people and no one can see anything wrong with the rod, rod bearing, or crank.
I really dont want to spend the money to get it rebuilt seeing as it only has 27k miles and doesnt appear to have anything wrong besides that. Anyone have any idea what is going on there or what to do to fix it? I was thinking of replacing the piston and just running it, but wanted to get some opinions from people with ls engine experience.

 

NW,
A picture would really help, otherwise just guessing. If you click on "post reply" and scroll all the way down on the page, you will see a box that says "manage attachments" If you click on that you can browse the pics on your computer and attach them to your reply.

If the pistons have a lot of carbon, that might have been what was actually making the noise if it was enough to actually hit the cylinder head.

Need picture

 

I bought a rolled Grand Cherokee years back and it had a light tap. Turned out to be a bent rod from when it got started with oil in the intake. Hydrolocked a cylinder and bent it a bit. Replaced the piston and rod and went 100k with it.

 

RED, a machine shop in colorado built a 370 engine for the engine masters challenge. they showed a picture of the long block with same marks your describing, but on all eight pistons. they called it really tight quench and shrugged it off. this was all in a article in popular hot rodding. good luck.

 

Thats sort of what I was thinking too but without pictures we will never know. I would bet there is something else causing the noise.