Damage To The Bucket Cylinder Due To Excessive Pressure Caterpillar

Problem:

Damage to the bucket cylinder can result from excessive hydraulic pressure that builds up due to incorrect operation or abuse of a bucket or work tool.

Solution:

Design changes will be effected to incorporate pressure relief in the hydraulic system for the bucket cylinder on 301.5, 301.6, and 301.8 machines. A design change is already effective with 302.5 (4AZ1944-UP) machines.

Pressure relief for the bucket cylinder and lines can be installed on all existing machines without a factory installed valve by following the instructions provided in this bulletin.

FIGURE 1. View of the bank valve that shows the location of the bucket control valve (A).

Instructions for Installing Pressure Relief on 301.5, 301.6, and 301.8 Machines

NOTE: No port is available on the existing bucket control valve for installing a pressure relief valve. It is necessary, therefore, to replace the existing valve with the new 201-0485 Block As. that includes pressure relief.

1. Remove the bank valve from the machine.

Refer to "Bank Valve-Remove" in the Disassembly and Assembly Manual for your machine.

2. Remove the bucket control valve from the bank valve.

Refer to "Bank Valve-Disassemble" in the Disassembly and Assembly Manual for your machine.

3. Reassemble the bank valve using the new 201-0485 Block As., the two new 139-5076 Seals, and the two new 139-5077 Seals.

Refer to "Bank Valve-Assemble" in the Disassembly and Assembly Manual for your machine.

4. Reinstall the bank valve in the machine.

Refer to "Bank Valve-Install" in the Disassembly and Assembly Manual for your machine.

Instructions for Installing Pressure Relief on 302.5 (4AZ1-1943) Machines

NOTE: Refer to the Disassembly and Assembly Manual for your machine for instructions on releasing hydraulic system pressure and for the warnings and notices associated with working on the hydraulic system.

1. Remove the plug from the port on the head end of the existing bucket control valve. See Figure 1.

2. Install the 140-5605 Valve As. in the open port on the existing bucket control valve.

Tighten the valve to a torque of 40 ± 5 N·m (30 ± 4 lb.ft.).

Reference: Disassembly and Assembly Manual, RENR2808, "301.5, 301.6, and 301.8 Mini Hydraulic Excavator Machine Systems"

Reference: Disassembly and Assembly Manual, RENR2848, "302.5 Mini Hydraulic Excavator Machine Systems"

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