Case 580SR, Service Manual

Page: 970 / 1068

142 SECTION 55 - ELECTRICAL SYSTEM
Armature
Z
The surface of the commutator must be clean and
without traces of burns. If necessary, remove trac-
es of burns using fine sandpaper. Do not use em-
ery cloth. Then, clean the commutator with a cloth
soaked in gasoline.
Z
After rectifying the commutator, polish it with fine
sandpaper, then wipe it with a cloth soaked in
gasoline.
NOTE: make sure not to graze the metal of the com-
mutator during rectification of insulating notches.
Z
The resistance of the armature insulation may be
checked by connecting an ohmmeter (1) between
the blades of the commutator (2) and the armature
shaft (3). The resistance must be infinite (no conti-
nuity).
Z
To check that the armature is not short-circuited, a
special device for armatures must be used. The
other solution is to replace the armature.
Z
If the circumference of the armature has come into
contact with the starter pole shoes, the bearings of
the armature are probably excessively worn out.
First check that the starter pole shoes have been
tightened and that the armature rotates without any
concentric defect. If necessary, replace the arma-
ture bearings.
Field coils
Z
To check the resistance of the field coil insulation,
connect an ohmmeter (1) between the brushes of
each induction coil (2) and a clean unpainted area
of the body (3). The resistance must be infinite (no
continuity).
Z
To check the continuity of the field coils, connect an
ohmmeter between the brushes of each induction
coil and the main supply terminal (the thickest
braided wire). The resistance must be equal to 1
MW.
Z
If the field coils are defective, the entire assembly
consisting of the body and the field coils must be
replaced.
Drive pinion
Z
The drive pinion must only rotate clockwise. If the
pinion is seized or turns in both directions or if its
teeth are damaged, change the complete drive as-
sembly.
NOTE: if the teeth of the drive pinion are damaged,
also check the teeth of the engine flywheel ring gear.
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