The slewing bearing (also known as a slewing ring) connects the excavator’s upper structure to its undercarriage and withstands all rotational movements, loads, and impact forces. Once it fails, replacement costs can reach tens of thousands of dollars, and the machine must be disassembled and separated. Most slewing bearing failures develop from minor issues. The following four inspections can help identify potential problems early.

1. Measure Vertical and Radial Clearance

Excessive slewing bearing clearance indicates internal wear. Park the excavator on level ground and place a dial indicator (or test indicator) against the outer ring (a feeler gauge method may also be used). Use the boom to push the upper structure sideways and measure radial movement; then use the boom to lift the machine and measure vertical movement. For a 20-ton-class excavator, vertical clearance exceeding 3 mm or radial clearance exceeding 2 mm indicates that the bearing needs to be replaced. It is recommended to check the clearance every 1,000 operating hours and record the measurements to track the wear rate.

2. Apply Grease According to Schedule

Slewing bearings require regular replenishment with fresh grease—typically every 50 operating hours under normal working conditions, and every 25 hours in dusty or humid environments. While injecting grease through the grease nipple, slowly rotate the upper structure until fresh grease is seen being expelled from the seals. If the discharged old grease is black or contains particulate contaminants, the bearing has been contaminated. If no grease is expelled from a certain point, the lubrication passage may be blocked—clear it first with a metal wire. Do not force grease into the bearing, as this may damage the seals.

3. Inspect the Seals

Rubber or polyurethane seals run around the top and bottom of the bearing to keep out dirt and moisture. Walk around the machine and inspect both seals for gaps, damage, or displacement from their mounting grooves. Damaged seals allow sand, dirt, and moisture to enter the bearing raceways, accelerating wear. Replace the seals immediately—they are inexpensive and easy to install compared with replacing the entire bearing.

4. Watch for Changes in Slewing Noise

Every operator is familiar with the normal operating sound of the slewing motor and bearing. Changes in sound are often an early warning of failure. Grinding, cracking, or irregular clicking sounds during rotation usually indicate damaged rollers or raceway spalling. Also watch for jerking during slewing or uneven rotational speed, as these may indicate internal damage. If abnormal noise is heard, stop slewing operations and visually inspect the bearing for excessive clearance or grease contamination. Do not continue working—if the slewing bearing seizes, it may cause irreparable twisting deformation of the upper frame.

Quick field check: With the engine shut down, manually rotate the upper structure slightly by hand (or by placing a pry bar against the track) and feel whether the movement is smooth. If it turns smoothly and freely, the condition is good; if it feels stuck or jerky, there is an internal fault in the slewing bearing.

Need an excavator slewing bearing inspection record sheet? Please reply with your equipment model and serial number, and we will send you a PDF file containing clearance measurement procedures, grease specifications, and a maintenance record template.