Originally Posted by Blazin72
I highly doubt the Gen III/IV (LS) engines have an INTERFERENCE fit between the pistons and cylinders. The engine wouldn't run, especially when you account for thermal expansion.
The sleeves may be interference fit between with the block on aluminum engines but I doubt the pistons are interference fit with the sleeves/cylinder bores.
This information came from my instructor Judson Massingill. He owns and instructs at the School of Automotive Machinists.
Don't know if you've ever press fit anything but a few tenths of interference fit is not much. Then you add the skirt coating that tends to retain a film of oil to itself and that would help with movement. With the operating temps, and again, again...hypereutectic pistons which do not expand more that a few tenths, the cyl will increase in diameter more than that by the time it reaches over 200* coolant temp. There is your clearance...the difference in expansion rate.