hi all im new here and need some help, i bought a 2001 astra 2.2 sri not long ago with head gasket fault, ive took head off had it skimmed and ready to put back together, but ive notice my first piston is a little lower down than the fourth when positioned to the top off block, is this a fault with the piston, the car run ok apart from white smoke when i bought it, answers would be appreciated, thank you.