BUSHING 9V4973 - Caterpillar

D353 EnginesDescription of Change: An improved keystone piston assembly is used on the above listed models. The top ring groove on the new piston assembly is .040" (1.02 mm) higher and the intermediate (center) ring groove is .040" (1.02 mm) lower than the top and intermediate ring grooves for former piston. The addition of .080" (2.03 mm) space between the top and intermediate ring grooves makes the piston stronger. This will prevent possible failures in the area between the top and intermediate ring groove.
Since the new piston has a top ring that is .040" (1.02 mm) higher than the top ring on the former piston, the new piston must not be assembled in a used cylinder liner that has a wear ridge (condition where two surface levels can be felt) near its top. This can cause damage to the piston ring and to the piston when the engine is started.
A procedure to remove the wear ridge in used cylinder liners will be given in Special Instruction SEHS7220.
Adaptable To: Direct replacement for the former piston assembly. The new piston assembly can also be used as a replacement for the earlier 3S5502 Piston Assembly when repairs are made to an engine because carbon deposits and ring sticking (holding) have caused too much oil consumption, damaged piston ring contact faces or piston seizure. The new piston gives better oil control and more resistance to ring sticking. Do not install one keystone piston assembly as a replacement for a 3S5502 Piston Assembly, but instead install a complete set of six keystone piston assemblies.