SHIM PACK 1643978 - Caterpillar

(51Z) Truck EnginesDescription of Change: For a period of time, a stepped compression ring was used on pistons in 3208 Naturally Aspirated Truck Engines. This ring is used in engines with serial numbers 51Z7065351Z72766. Effective with 51Z72777, the former ring is reinstated. This change was made to evaluate the effects of the step-type ring on emissions and oil control.Adaptable To: The stepped 2W2178 Ring can be installed if desired in all earlier 3208 NA Truck Engines as a direct replacement for the former 9L6233 Ring or earlier compression rings. Install the ring so the step is on the bottom face of the ring. (See Special Instruction SMHS8409-01 packaged with the ring.) The word "UP" appears on the other side of the ring. The 2W2178 Ring has been available for parts service and used in rebuilt engines for several years.