Commentator

ELECTRICAL

connected. Place one prod of test lamp on

armature and the other prod on commutator. (Fig.

33) If test lamp lights, armature is grounded and

should be replaced if defect is not readily

apparent and repairable.

b. Place armature on growler. Hold hacksaw

blade over armature and slowly rotate armature.

If saw blade vibrates, armature is short-circuited.

Before replacing, inspect commutator slots for

copper or brush dust deposits. Clean thoroughly

and retest.

c. Burned commutator riser bars are sometimes

caused by an open-circuited armature. If bars are

not too badly damaged, armature can sometimes

be repaired by resoldering the leads in the riser

Figure 37

bars, using rosin flux solder. After soldering, turn

down commutator and undercut the mica.

3. Field Coils

d. Examine bearing surfaces at each end of

NOTE: Before checking field coils on

armature shaft for evidence of wear, and examine

enclosed

shift

lever

starter,

spiral splines for damage. Replace armature

disconnect shunt field coil lead from

assembly if shaft is worn or damaged.

brush holder bracket.

2. Commutator

a. Place one test prod on field coil connector and

the other on each field coil lead. If lamp does not

a. Inspect commutator and if found to be rough,

light, coils are open-circuited.

out-of-round, worn or has high mica, filled slots, or

is burned, repair as follows:

b. Place one test prod on field frame and the

other on each field coil lead. If lamp lights, coils

b. Turning Down. Place armature in a lathe and

are grounded.

turn down commutator to remove worn spots, out-

of-round, or rough condition. Do not cut deeper

c. If ground or open circuit is indicated in series

than necessary to clean up. (Fig. 37)

connected coils, break the connection between

coils and test each coil separately to determine

c. Undercut Mica. Mica between commutator

which one is defective and must be replaced. If

segments must be below edges of segments.

any coil is replaced, make sure connections are

Start groove with a small three-cornered file, then

securely soldered and properly insulated.

use a hacksaw blade to undercut mica to a depth

of 1/32 inch. Use No. 00 sandpaper to clean and

smooth up commutator, then blow all dust and

cutttings out of grooves.

B-77