Service Manual

Testing
(USE TESTING SECTION FROM ONAN MANUAL, PAGES 9-3 THROUGH
9-5.)
Inspect the starter components for mechanical defects before testing for
grounds or shorts.
Testing Armature for Grounds: Connect 1 lead of an ohmmeter to the
armature shaft or core. Touch the other ohmmeter lead to each of the
commutator bars in turn (Figure 1). A low ohmmeter reading indicates a
grounded armature. Replace grounded armature.
Testing Armature for an Open Circuit: Using an ohmmeter, check for
continuity between the commutator segments. If there is no continuity
(high resistance), the segments are open and armature must be replaced.
Testing Armature for a Short Circuit: Use growler for locating shorts in the
armature (Figure 2). Place armature in growler and hold a thin steel blade
(e.g. hacksaw blade) parallel to the core and just above it while slowly
rotating armature in growler. A shorted armature will cause the blade to
vibrate and be attracted to the core. If the armature is shorted, replace
with a new one.
Commutator Inspection: If the commutator is dirty or discolored, clean with
number 00 to 000 commutator paper. Blow grit out of armature after
cleaning.
If the commutator is scored, rough, or worn, turn it down in a lathe.
Field Coil: Use an ohmmeter to check for continuity between brushes. If
there is not continuity, the field coil is open and must be replaced. With the
field coil mounted in the frame, check for continuity between the field coil
and frame. Replace frame assembly if there is continuity.
Brushes: Clean around brushes and holders, wiping off all brush dust and
dirt. If brushes are worn shorter than .4528 inch (11.5 mm), replace them
(Figure 3).
Check for shorts between positive side of brush holder and brush holder
base. If there is continuity, replace holder assembly. Check for free
movement of brushes. All brushes should move freely in the brush holders.
Commutator Bars
Figure 1
HacksawBlade
Growler
Figure 2
.4528 inch
(11.5 mm)
Brushes
Wear Limit
Figure 3
Starter
Electric
Glossary
GLOSSARY
3-20 Demystification Guide