VALVE GP-RELIEF 7G4491 - Caterpillar

All 3408, 3412 Engines Equipped With Precombustion ChambersReference: Engine News; October 1987; Page 6; "New Steel Fuel Injection Pump Lifters Should Not Be Mixed With Aluminum Lifters" 3400 Family Of DIT Engines.Pitting, spalling, and wear can occur on the lobes of the 4N0599 and 4N0602 Camshafts in the fuel injection pump groups for 3408 and 3412 Engines respectively. This problem has been found in the paths where the rollers for the 3S9736 Lifter Assemblies travel over the camshaft lobes.
If pitting, spalling or wear is encountered on the camshaft lobes, Caterpillar recommends installing a new camshaft (the same part number) and different lifter assemblies. Along with a new camshaft, install 8N6981 Lifter Assemblies instead of the original 3S9736 Lifter Assemblies. The 8N6981 Lifter Assemblies have wider rollers which will reduce the stress placed upon the camshaft lobes. Thus, the components will have longer service life.
Do not reinstall a used camshaft with new 8N6981 Lifter Assemblies unless the fuel system was originally equipped with 8N6981 Lifter Assemblies.