Remove sleeve bearings with arbor plates and an
arbor press. When an arbor press isnt 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
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
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
4. Clean, inspect, and store the brushes and brush
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
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
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
1. Support the armature or rotor only by its shaft
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 doesnt light, the
winding is open. If it does light, an open circuit doesnt
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 the