1998/02/02 Caterpillar

793C (4AR) Off-Highway Trucks

Description of Change: A new wear ring for the intermediate cylinder assembly and improved wear rings for the piston and rod prevent the hoist cylinder group from binding.

The former wear ring, for the intermediate cylinder assembly and earlier wear rings for the piston and rod, enlarged slightly as hydraulic oil increased in temperature.

Enlarged wear rings caused the intermediate stage of the hoist cylinder to bind. Binding of the intermediate stage caused erratic movement of the truck bed when lowered.

The new wear ring (two each), for the intermediate cylinder, is narrower with a wider gap at the ends.

The later wear ring, for the piston, is narrower with a wider gap at the ends.

The later wear ring for the rod is narrower.

Adaptable To: The new 153-0119 Ring-Wear (1) is a direct replacement for former 121-4176 Ring-Wear (2).

Later 121-4175 Ring-Wear (3) replaced earlier 121-4175 Ring-Wear (3) and later 121-4703 Ring-Wear (4) replaced earlier 121-4703 Ring-Wear (4).

New 153-0119 Ring-Wear (1), later 121-4175 Ring-Wear (3), and 121-4703 Ring-Wear (4) were effective with 121-2071 Cylinder Group (Eng. Chg. 03) and are adaptable to earlier 121-2071 Cylinder Groups (Eng. Chgs. 00-02).

NOTE: An engineering change number (Eng. Chg.) indicates effectivity of this improvement or adaptability to previous cylinder groups. The cylinder group part number, engineering change number, and date of manufacture are found on the cylinder group tag.

(A) Wear Ring (Intermediate Cylinder).

(1) New 153-0119 Ring-Wear.

(F) 101.25 mm (3.986 in).

(M) 7.00 mm (.276 in).

NOTE: Check gap (M) when assembled on a 317.27 mm (12.491 in) dia. disc or on intermediate cylinder.

(2) Former 121-4176 Ring-Wear.

(G) 101.64 mm (4.002 in).

(N) 2.00 mm (.079 in).

NOTE: Check gap (N) when assembled on a 317.27 mm (12.491 in) dia. disc or on intermediate cylinder.

(B) Later wear ring (piston).

(3) 121-4175 Ring-Wear.

(H) 48.37 mm (1.904 in).

(M) 7.00 mm (.276 in).

NOTE: Check gap (M) when assembled on a 247.42 mm (9.741 in) dia. disc or on piston.

(C) Earlier wear ring (piston).

(3) 121-4175 Ring-Wear.

(K) 48.75 mm (1.919 in).

(N) 2.00 mm (.079 in).

NOTE: Check gap (N) when assembled on a 247.42 mm (9.741 in) dia. disc or on piston.

(D) Later wear ring (rod).

(4) 121-4703 Ring-Wear.

(R) 74.32 mm (2.926 in).

(W) 5.00 mm (.200 in).

(E) Earlier wear ring (rod).

(4) 121-4703 Ring-Wear.

(T) 74.70 mm (2.941 in).

(W) 5.00 mm (.200 in).

NOTE: Check gap (W) when assembled in a 203.40 mm (8.008 in) dia. ring or in rod.

121-2071 Cylinder Group-Telescoping