HUB 4520600 - Caterpillar

Introduction
ReferenceThis technical information bulletin replaces a technical information bulletin that was written on 20October 2000. Please disregard Technical Information Bulletin, TIBU4388-00, "Buffer Seal Failure Caused by a Defect in the Seal Groove on all Medium and Large Track-Type Tractors, Large and Medium Wheel Loaders, Hydraulic Excavators, and Backhoe Loaders built after 1January 2000". Refer to the following technical information bulletin.Problem
Information from the field has indicated that the backup ring for the buffer seal can wear a step in the groove for the buffer seal in the cylinder head that causes the buffer seal to fail. This causes leaking from the rod end of the cylinder. The material for the backup ring is not as hard as the head material. In some applications, the backup ring wears the head material. The groove has only been seen in cylinder heads that contain the new buffer seals that are yellow.
Illustration 1 g01327275
Refer to Illustration 1. Step (1) in the groove for the buffer seal will be found in the corner of the groove for the buffer seal. The failures that have been seen in the field have been found after the cylinder head has accumulated many hours of operation. When you install new seals in a leaking cylinder, it is possible that the wear groove would not be detected because the wear is located in an interior groove in the head.Solution
Illustration 2 g01327277
When you install new seals in a cylinder for any reason, perform a thorough inspection on any cylinder head that uses the new design of seals that are yellow. Determine if there is a groove or a recessed area on the edge of the groove for the buffer seal. If a defect is found, replace the head. Refer to Illustration 2. If seal groove (2) does not have any wear, Reuse the head.