Chapter 5 General Reference 123
Turntable Bearing Inspection for Replacement
Before a bearing is removed from a crane for inspection, one of the following conditions should
be evident:
1 Metal particles present in the bearing lubricant.
2 Increased drive power required to rotate the crane.
3 Noise emitting from the bearing during crane rotation.
4 Rough crane rotation.
5 Uneven or excessive wear between the pinion gear and turntable gear.
If none of the listed conditions exists, the bearing is functioning properly and need not be
replaced. But, if one or more of the above conditions exists, inspection may be required. Limits
are measured in “TILT” which is dependent on the internal clearances of the bearing. TILT is the
most practical determination of a bearings internal clearance once mounted on a crane.
Periodic readings indicating a steady increase in TILT may be an indicator of bearing wear.
Note that a bearing found to have no raceway cracks or other structural irregularities should be
reassembled and returned to service.
Turntable Bearing Tilt Test
1 With the crane horizontal and fully extended, measure between the top and bottom mounting
surfaces of the turntable bearing (A1), using a dial indicator for accuracy.
2 Reverse the load by applying minimal downward pressure on the boom while the boom is in
the boom support or on a solid surface. Again measure A2.
3 Subtract A1 from A2 to determine tilt and compare the result with the accompanying chart.
A1
A2
Boom Suppor
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