LS2 engine rebuild - help needed for piston size...

[tmcorvette]

My friend is rebuilding his 2005 LS2 engine after an engine failure and just received the new pistons.

But, there might be a problem with the pistons. The GM part number for stock size LS2 pistons is 19178305, this is what he received, but after measuring the pistons, they are "oversized", by 0,04-0.05 mm compared to the old ones. We think that the first oversize is 0,020" = 0,5 mm, so these are not oversized ones.
Does anybody know why they are bigger, and what do we have to do with the block itself? We want to make sure if we need to do any work on the block/cylinder...

Bore:
1. 101.64 mm
2. 101.63 mm
3. 101.62 mm
4. 101.64 mm
5. 101.64 mm
6. 101.63 mm
7. 101.64 mm
8. 101.63 mm

New piston : 101,61 mm
Old pistons: 101,56-101,57 mm

Any help will be greatly appreciated. Thanks!

[c4c5specialist]

HI there,

Take a look at your piston to bore specification.

Those pistons are correct.

Allthebest, c4c5

[tmcorvette]

Thank You! We were just not sure the piston to bore clearance can be 0.01 mm...

[Hib Halverson]

LS2 pistons when new may have very tight or even negative piston-to-bore clearance. This is due to the polymer coating on the skirts which is partially-sacrificial.

Very soon after the first start-up, some of the coating wears away leaving the proper piston-to-bore clearance.

Once you get the short block assembled you may also find negative deck height.

[tmcorvette]

Thanks for your explanation!