D330C, 3304, D333C, 3306 Industrial and Marine Engines;
1673C, 3306 Truck Engines;
D7G, 627B Tractors;
627B, 637D Scrapers;
571G, 572G Pipelayers;
235 Front Shovels;
Description of Change: New basic piston groups are used in rod and piston groups for the above models. The pistons used in the new piston groups have the piston pin bore moved off-center .06" (1.5 mm) away from the thrust side of the piston. This lowers the thrust loads so there is less vibration or movement of the cylinder liners, and less liner pitting. Formerly, vibration or movement of the cylinder liners caused liner pitting, especially during operation under heavy load conditions.
Adaptable As: Direct replacement. For engines equipped with keystone-type piston rings, use the new *9N5404 Piston Group (Basic) in place of the former 9N1303 Piston Group (Basic), which is canceled. For engines with rectangular cross section piston rings, use the new **9N5251 Piston Group (Basic) in place of the former 4N9258 Piston Group (Basic), which is canceled. Check the engine arrangement and parts book to see which piston group is needed. The new and former pistons can be mixed in the same engine; it is not necessary to install a complete set of new pistons. The piston rings used in each of the piston groups are not changed.
*Not available as a group. Order 9N5403 Body Assembly and 9L6935 Ring Group.
**Not available as a group. Order 9N5250 Body Assembly and 9S3068 Ring Group.