I am currently rebuilding a 5.3 out of a 2000 Chevy Silverado for my v6 99 Camaro. Im having a little trouble with my pistons. This is the first motor I have built and im not sure what a .030 over bore should look like so bear with me. I got my blocked bored and I noticed the old pistons still fit snug but the new ones dont even go in. Dont roast me too bad. Are these pistons just too big or did the machine shop screw me?

 

Check the old and new piston with a caliper. That'll tell you what you have and then get yourself some inside gauges and stick them in the bore(very carefully as to not scratch it) and measure that with the calipers. There should be a slight difference in the piston and bore anyway which is taken up by the rings. Are you aware you need a proper compressor to get the piston+rings into the bore?

 

did the shop have the new pistons to fit when they bored the block?

 

Uh, 4 ring grooves? What is that piston really for? It should look like this one.

 

Thats odd. Really old engines used 4 rings, and the compression height is way higher than the stock one. I'd bet the machine shop gave you someone elses stuff by mistake.