Engine Builders-KB356 Piston Milling

To get the proper measurement, the piston must be in the bore. ALL of the volume above the top ring is part of the equation. The way you're measuring the piston out of the bore will be inaccurate, since it does not include everything above the top ring. You'll also not know "where" the piston is in the bore, until you actually measure, as your block maybe different than the next, so you will have to measure.