Pivoted Shoe Journal Bearing Clearance Check
Bearing clearance is one of the critical dimensions of any pivoted shoe journal bearing. Many times the amount of clearance determines how well a machine will operate. Measuring bearing clearance will allow you to determine if the bearing is worn and should be replaced. In this article we will instruct and show you how to measure the clearance of your Orion Pivoted Shoe Journal Bearing.
The following items are required.
- Tools to assemble and disassemble the bearing
- Shaft size mandrel and base plate
- Dial indicator
The first step is to disassemble the bearing and thoroughly clean all the components. They should then be blown or wiped dry. Clean components are critical to obtaining an accurate measurement. Dirt located in the pivot areas or at the split line of the bearing will produce larger or smaller measured clearance values. A visual inspection of the components should also be made. Signs of wear in the pivot holes or on the pad pivots are indications that the bearing may be worn and out of tolerance.
The next step is to obtain a mandrel with a diameter equal to that of the shaft. A diameter larger or smaller than the shaft will not provide an accurate clearance reading. One end of the mandrel should be perpendicular to the turned diameter. The mandrel should then be bolted to a clean flat heavy plate with a surface that preferably was ground.
Clamp the mandrel and base plate assembly securely to a table. Incorrect clearance could be obtained if this assembly is not firmly attached to the table. Assemble the bearing assembly around the mandrel as shown in the figure below. The bearing components should be dry for this inspection, do not oil the components. Using a rubber hammer, lightly tap the bearing retainer at each shoe location. This process insures that each of the bearing shoes is properly seated in the retainer pivot holes.
Place the dial indicator on the table and locate the indicator on the outside diameter of the bearing as shown in the figure below. Rotate the bearing until one of the bearing pivot holes is directly in line with the dial indicator (see photos). Move the bearing assembly in a direct line with the indicator until the indicated pad is contacting the mandrel. Set the dial indicator to zero. Move the bearing assembly, through the clearance, in a direct line with the indicator. Make several measurements until you achieve approximately the same reading each time. Record the reading for this pad location.
Rotate the bearing to the next pad location. Set the dial indicator to zero and make several measurements of the bearing clearance. Repeat this step for each pad.
The measurement that has been made is considered to be the Measured Bearing Clearance. When measuring a 4 pad bearing, this is also the running clearance. However, for a 5 pad bearing, the results must be adjusted to obtain the running clearance. This adjustment is required due to the larger clearance that is measured as the mandrel contacts the bearing bore on one pad and then between the opposite pads. Therefore, use the following calculation to obtain the running clearance.
Running Clearance = Measured Clearance x 0.8944
Finally compare the running clearance to the values shown on the bearing assembly drawing. If the clearance values are to large or to small, make sure the bearing is properly assembled and that the shoe pivot areas and bearing split line are clean.
View the Clearance Check video (640KB)