How can you tell if your piston is stock?

[jtomasi1]

How can you tell if your piston is stock? Mine had a small S inside of it.

 

[dirtyblaster]

take a pic if the piston then we can help ya

 

[Roccdeezy]

Mearure the piston. It should have a diameter of 66 milimeters(stock). For every .25 millimeters over that it has been bored .010 over. For example a 67 milimeter piston would be bored .040 over. I'm not sure on conversions but you could measure in inches and try to convert it to metric but really you need a metric micrometer. Also I'm pretty sure it is stamped on the piston. If all it says is S then i'm going to go out on a limb and say it is stock.