In previous tips, we discussed the dangers of over-greasing the swing bearing and how to do a basic "rock test" to check for play. But on a high-hour machine (8,000+ hours), the rock test is too subjective. If you want to know if a $20,000 swing bearing is truly worn out, or if you just have a loose swing gear, you must use a dial indicator to measure axial and radial clearance.
First, park the machine on flat, solid ground-never on dirt or gravel, as the track frame will flex and give false readings. To measure axial clearance (vertical play), mount the magnetic base of the dial indicator on the rotating house, and place the indicator tip on the top machined surface of the undercarriage frame. Have an operator sit in the cab and push the boom down to lift the front of the tracks off the ground slightly, then lower it back down. The dial indicator will show the exact thousandths of an inch the bearing is moving vertically.
To measure radial clearance (side-to-side tilt), mount the indicator base on the undercarriage frame, with the tip touching the vertical machined lip of the upper house. Have the operator push the heavy boom fully to the left, then fully to the right. The indicator will show the horizontal tilt. Most manufacturers publish a reject specification (often around 0.030 to 0.040 inches of axial play). If the dial indicator exceeds that spec, the bearing races are permanently brinelled, and the machine is an accident waiting to happen. Guessing with a rock test will cost you money; measuring with an indicator saves it.
