When you changed you piston did you change your bore? My shop is saying that I should change the bore to the next size piston. He says that the new piston should be bigger because it is broken in for the stock piston/ bore.
Any help?

 

Your shop is right from their point of view. The typical shop would not want to stand behind a rebulid that was done "piecemeal". If you are doing it yourself or don't expect a warranty from the shop you can change just the piston/rings if there is absolutely no wear on the cylinder. You will need to hone or break the glaze on the cylinder surface to get the new rings to seat. If it was me i would bore the cylinder to the next size, usually .5mm or .020 inch. That way you would know pretty much for sure that you won't have any ring seating problems or piston skirt clearance problems. To much piston skirt clearance can cause piston skirt breakage at high rpms.

 

You don't have to go to a big bore if you don't want to. If you want to keep the stock bore, just hone your cylinder..it will be fine. I run a 12:1 stock bore piston right now with no problems.

 

I just had a JE 11:1 piston and Stage 1 Hot Cam put in mine and they just honed the cylinder with no problems whatsoever!!!!!!!![img]i/expressions/face-icon-small-happy.gif[/img]

 

Have them check the cylinder too see if it is within tolerence. How many hours are on the machine? You would be surprised too find most shops can't manage too do a proper bore.