On this parts fiche the Pin, Dowel B (664) is the most specified component.
Parts such as the Crank - Piston: O-ring (683), Washer, Piston Pin, Piston (0.50mm O/s), Gasket, Oil Seal Housing (nas) are included in the P50trp 1991 Crank - Piston parts fiche.
The twenty-one P50trp 1991 Crank - Piston component parts are all listed in this schematic.