COMPUTER 4726821 - Caterpillar

Illustration 1. Location of the new rod seals and the added wear ring in the new cylinder heads. The most common location of the wear ring is to the inside of the three seals as shown....A double lip wiper seal has replaced the single wiper seal. The double lip seal is more effective in preventing either dirt from entering the sealing area or oil from seeping out.
...New cylinder heads are used that have a groove added for a wear ring. (Wear rings have been used on the cylinder pistons for several years.) The head wear ring reduces scoring of the cylinder rod, and helps to center the rod in the seals. The location of the wear ring in the head depends on the length of the cylinder rod. In most cylinders, the wear ring is positioned to the inside of all three seals as shown in Detail (A) in Illustration 1. On cylinders with longer rods, where there is a possibility of some cocking of the piston against the cylinder wall, the wear ring is positioned between the wiper seal and the U-cup seal. See Detail (B) in Illustration 2. This gives the longest possible support distance between the piston wear ring and the head wear ring.
Illustration 2. Location of the wear ring in heads with the longer cylinder rods. The relative position of the three seals to each other is the same regardless of the wear ring position.Part numbers of the cylinder groups did not change as a result of these changes.
Adaptable To: The new two piece-step buffer seal and double lip wiper seal can be used as direct replacements for the former seals. It is best to use both new seals together to get the most benefits of improved sealing and longer life of the U-cup seal. The former seal groups have been canceled and replaced by new seal groups which contain the new buffer and wiper seals. The step buffer seal must be installed with the cutout (step) on the inner seal toward the piston end of the head, or away from the U-cup and wiper seals. Put 7M7456 Bearing Mount in the head counterbore for the new wiper seal, and on the seal case to prevent pressure from loosening this seal. Special Instruction SEHS8905, "Installation Of The Step Buffer Seal Assembly, U-Cup Seal, And Double Lip Wiper Seal In Hydraulic Cylinders", comes with each seal group. A 4C4069 Installer is needed to install the 8C9122 Buffer Seal Assembly for 38.1 mm (1.5") diameter rods, and a 4C4070 Installer is helpful to install the 8C9123 Buffer Seal Assembly for 44.6 mm (1.75") diameter rods.The new and former buffer and wiper seals are listed in the chart by rod size.
It is not necessary to machine a groove in earlier heads to accommodate the added wear ring. Earlier heads are hardened and have a smaller inside diameter to give more support to the rod. However, these rings can, if needed, be installed in earlier heads. Refer to