Remove sleeve bearings with arbor plates and an arbor press. When an arbor press isn't available, sleeve bearings may be removed with a well- fitted arbor and hammer.
Sometimes you may be required to remove sleeve bearings by drilling them out with a drill press.
Handle bearings with clean, dry hands or clean canvas gloves. Handling a bearing with hands that are perspiring can cause corrosion. Fingerprint patterns are sometimes found rusted into bearing surfaces.
Keep bearings in their packages or in oil-proof paper until they are installed
Brush Removal. - Brush removal is necessary when you are replacing brushes or you need access to parts of the unit otherwise inaccessible. If the brushes are not to be removed, place them in the raised position. Use the following procedure for removing brushes and brush rigging:
1. Record the placement and angle of brush rigging and brushes.
2. Check the brush spring pressure.
3. Remove the screws holding the brush pigtails and rigging.
4. Clean, inspect, and store the brushes and brush rigging.
Centrifugal Switch Removal. - Internal switches of the centrifugal type are usually attached to the inside of end bells. When you are removing the end bells, be careful not to break the switch springs. For removing a centrifugal switch, follow these steps:
1. Note and record the lead connections to the switch.
2. Disconnect the leads.
3. Remove the mounting screws of the stationary part of the switch which is secured to the end bell.
4. Clean and inspect the switch and replace the damaged parts.
5. Tag and store the unit.
Armature and Rotor Removal. - The removal of armatures and rotors from within the frame of the unit requires considerable care to avoid damage to the parts.
For removing an armature or rotor, follow these suggestions:
1. Support the armature or rotor only by its shaft when possible.
2. Slide a thin piece of cardboard between the underside of the rotor and stator to protect the laminations and windings during rotor removal.
3. In a shop, a hoist should be used to remove the rotors of large motors.
TESTING COMPONENTS. - After a motor is disassembled, you perform certain tests to determine which components are faulty.
Field Winding. - To locate a grounded field winding, disconnect and separate the internal connections between the windings. With this done, position one lamp prod of a series test lamp to the housing. With the other test lamp prod, touch each winding lead individually. If the test lamp lights, that particular winding is grounded. Test all the windings. You may also perform this test with an ohmmeter. A reading of continuity indicates a short; no reading indicates that the field winding is not grounded.
The test for an open circuit in the field windings of a motor may also be done with a series test lamp. Touch one test lead to one coil terminal and the other lead to the opposite coil terminal. If the test lamp doesn't light, the winding is open. If it does light, an open circuit doesn't exist, and the winding is serviceable.
To test for shorts in the field winding of a motor, you can compare the relative voltage drop in each field winding section with a voltmeter. You should get the same reading for each section. A decrease in voltage drop in a section indicates a short circuit.
Armature Winding. - The first test on an armature winding should be to locate grounded circuits. This test is also performed with a series test lamp. Touch one test prod to the armature core or shaft, as shown in figure 7-58. Using the other test prod, touch each commutator segment. If the armature winding is grounded, the test lamp will light when you apply the lamp prod to the grounded armature winding or commutator segment. Replace the grounded armature when all attempts to remove the ground have failed.
When checking for a shorted armature, place the armature in an armature test set (growler). Lay the test blade lengthwise with the flat side loosely in contact with the armature core, as shown in figure 7-59. Turn the test stand to the ON position and slowly rotate theContinue Reading