Fault Phenomenon: Caterpillar 336 excavator abnormal noise during swing, inspection reveals loose swing bearing mounting bolts.

Troubleshooting Process:
– Checked bolts: high-strength bolts fatigued and loose.
– Checked washers: washers failed or missing.
– Checked torque: not tightened to specified torque.
– Checked threads: threads damaged.

Root Cause: The swing bearing mounting bolts were not tightened to the specified torque and sequence, causing loosening due to vibration.

Required Parts: High-strength bolts and washers, retighten.