Fitting Pistons
- Arrow on piston heads indicate direction of installation. Weight class is indicated by a "+" or "-" sign. All pistons must be in same weight class. Maximum weight difference between pistons is .35 oz. (10 g).
- Measure piston diameter 90 degrees to pin bore and at specified height from bottom of piston skirt. See Fig 1. Piston crown is stamped with diameter and arrow of installation direction.
- Measure cylinder at top, middle and bottom. Out-of-round must not exceed .0012" (.030 mm). Taper should not exceed .0008" (.020 mm). If oil clearance is excessive, bore and hone cylinder block for installation of oversize pistons.
Courtesy of BMW OF NORTH AMERICA, INC.