Fitting Pistons

With piston removed and disassembled from connecting rod, measure diameter of piston. Measure with micrometer positioned 90° from pin hole and at a point measured from bottom of piston skirt. (Distance "A" in illustration.)

NOTE: Distance depends on engine and manufacturer of pistons.

Application	Manufacturer	Distance "A"
530i, 633CSi	Mahle	630" (16.0 mm)
530i, 633CSi	KS	947"(24.05 mm)
733i	Mahle	1.024" (26.0 mm)
733i	KS	1.340" (34.05 mm)

Fig 1: View Showing Correct Procedure to Measure Piston Diameter

Courtesy of BMW OF NORTH AMERICA, INC.

Measure inside diameter of bore in crankcase. If clearance exceeds specification, crankcase must be bored for next oversize piston. Pistons are available in 0.010" (0.25 mm) and 0.020" (0.50 mm) oversize.
Check piston ring side clearance and end gap. If new rings are installed, install with word "TOP" stamped in ring toward top of piston.