1997/09/22 Caterpillar

D11N (4HK, 74Z) Track-Type Tractors;
776C (2TK),
784B (5RK) Off-Highway Tractors;
776B (6JC),
777B (4YC),
777C (4XJ),
785 (8GB),
785B (6HK),
789 (9ZC),
789B (7EK),
793 (3SJ),
793B (1HL) Off-Highway Trucks;
994 (9YF) Wheel Loaders;
5130 (7TJ, 5ZL),
5230 (7LL) Excavators

Reference: Service Magazine, August 14, 1995, page 9, "New Piston Crown Assembly Used In Piston And Rod Group"

Description of Change: Several improvements have been made to the rod and piston group in the above machines powered by 3508/3512/3516 Engines. An improved piston crown has replaced the former piston crown. The improved piston crown is made from a new forging and has copper/aluminum bushings instead of steel backed bronze bushings. The improved piston crown is made from a simple forging that lowers stress in the piston making it stronger. The copper/aluminum bushings have a higher fatigue strength. When used together these improvements make the piston crown more robust.

NOTE: The piston crown bushings are not serviceable.

The improved piston crown assembly uses a different top ring, intermediate ring and oil ring. These rings are the same as the rings used on the 3500B piston crowns. A different piston skirt should be used with the improved piston crown assembly.

NOTE: If necessary, the previous 6I-2863 Piston Skirt can be used with the improved piston crown.

The piston rings used in the piston crown assembly are improved and will help lessen wear between the piston rings and the ring grooves. The improved top ring has an asymmetrical face, providing for lower brake specific oil consumption of the engine.

The improved piston skirt has an improved method of draining oil out of the piston crown cooling galley. With the improved piston skirt, more oil drains toward the under side of the crown. Less oil drains toward the cylinder liner. Lower oil consumption and less buildup of oil and carbon on the ring lands and in the ring grooves are the result.

Adaptable To: The improved 133-8383 Piston Crown Assembly replaces the former 121-0463 Piston Crown Assembly in the above machine engines. The improved 133-8383 Piston Crown Assembly and former 121-0463 Piston Crown Assembly are components of the 6I-2861 Piston And Rod Group. The 121-0463 Piston Crown Assembly has been discontinued.

The improved 122-5956 Piston Ring (Top) replaces the former 8N-1233 Piston Ring (Top). The improved 123-8216 Piston Ring which is the intermediate ring, replaces the former 8N-7810 Piston Ring (Intermediate). The improved 123-4268 Piston Ring (Oil Regulating) replaces the former 7W-2221 Piston Ring (Oil Regulating). The former piston rings are still serviceable because they must be used on the former piston crowns and on 3500 one piece pistons.

The improved 125-2782 Piston Skirt should be used with the improved 133-8383 Piston Crown Assembly. The 125-2782 Piston Skirt may be used on any 3500 piston crown with a 19.0 mm (.75 in) top ring position. The 3500, 6I-2862, 114-0382, and 121-0463 Piston Crowns have a 19.0 mm (.75 in) top ring position.

NOTE: The following lists the lube oil requirements for engines with the 133-8383 Piston Crown Assembly:

* Use Caterpillar diesel engine oil CG-4.

* When Caterpillar DEO is not used, a multigrade API CG-4 is preferred. A multigrade API CF-4 is acceptable.

* The obsolete API specifications CC, CD, CD-2, and CE are not acceptable. The current API classifications CF, and CF-2 are not acceptable.

NOTE: When using the improved 133-8383 Piston Crown Assembly, the improved piston rings MUST be used and the improved piston skirt should be used. When used together, the above parts are adaptable back to first production of the above machine engines.