The BMW specification for the radial clearance of the conrod big end & crankpin is based on the use of slightly spherical rollers in some of the crankshafts.
The use of spherical rollers prevents the rollers from “biting” when the crankshaft flexes at high RPM.
Today the new FAG Dürkopp conrod sets are equipped with cylindrical rollers.
This requires a slightly larger radial clearance to prevent the rollers from getting stuck when the crankshaft flexes at high RPM.
Spherical rollers (used) are identified by the wear track in the center of the roller:
