Harley Davidson Sportster (1959 to 1969). Service manual - page 12
Repeat the test between all segments, turning the armature so each test
is made in the same position relative to the growler. If an open circuit
is found, check for loose or broken wires at commutator connections. If
none are found that may be repaired, armature must be replaced. All
soldering should be done with rosin flux.
REPAIRING COMMUTATOR
A generator that has been in extended service may fail to deliver enough
current to keep the battery in a charged condition although its field
coil and armature windings are in serviceable condition. In such cases
the commutator and/or brushes are usually at fault. If the commutator
has been worn down until the mica separations between segments are no
longer undercut or recessed, the commutator probably is grooved
noticeably in path of brush travel and no slot between commutator
segments exists, causing the brushes to ride high and make only
intermittent contact with commutator.
The commutator may be turned down in a lathe and sanded with fine
sandpaper until true and smooth. Mount armature in lathe on its bearing
seats not on shaft centers. Never sand a commutator with emery cloth.
Particles will imbed themselves in the copper surface, holding the
brushes off the commutator far enough to cause heavy arcing and burning.
After commutator has been turned down, the mica
insulation between segments must be recessed or undercut approximately
.025 in. Undercutting is usually done with a special undercutting
machine. If one is not available, satisfactory undercutting may be done
with a piece of hacksaw blade. Carefully thin down blade width, if
necessary, until offset saw teeth are the same width as slots in
commutator. Slots must be square-bottomed for good results. See Fig.
5E-6.
Sand commutator surface on lathe and repeat growler test to be sure
there are no copper particles between segments.
Open circuited armatures can often be repaired. The break or opening in
the circuit usually occurs at the commutator riser bars, a result of
overloading the generator which causes overheating and the melting of
solder at the joint. Resolder the leads in the riser bars using rosin
flux. Turn down commutator and sand to remove any burn spots as
described in previous paragraph.
POLARIZING GENERATOR
Assemble generator as described in ’’Assembling Generator.” After a
generator has been repaired, it must be repolarized to make sure that it
has the correct polarity for charging in the right direction.
