ok took my evo 7 block to the machine shop, the block i brought was all ready bored out 0.5mm o.s/3.661'' o.s. to suit my pistons so i was told i would need a light hone as it was in used condition. my problem is that ive got to set my ring gap and the gap is all ready 0.5mm with no filing! took it back to the shop and he said it would be fine?? is he just trying to cover his *** or is this going to fail!

 

Depending on the ring brand and how the engine is going to be used, it might even be perfectly to spec. Also you didn't mention top ring or second ring. The second ring needs to have a larger gap by a couple thousandths. My wiseco 87 mm pistons' narrowest recommended gap (for the second ring) is .016, the widest gap was .024. If you're going to be making really big power, wider ring gaps are necessary to prevent the ring gap closing completely and damaging the engine. The downside to that is the potential to burn a little oil. Personally, I prefer a wider gap because it leaves a margin for safety in case things get too hot.

 

yea sorry the top rings are .5mm,, they are CP pistons and jst nitrated rings. also dose anyone know the max clearance the piston can have?

 

Contact CP.

 

.5mm is ok...very common.