Starting System - Onan MJA Series Service Manual

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STARTING SYSTEM
electrical connection holding it to the motor frame. Remove the 2
screws on the rear of the solenoid to reach the switch contacts.
9. On early models only, if it is necessary to remove the starting
motor flange (Fig 3. 6.E), watch for shims between the flange and
crankcase surface. Save any shims, they must be reinstalled to
position the starter correctly.
3.6.4 REPAIR, STARTING MOTOR
3.6.4.1 Armature. - Inspect the armature for mechanical defects
before checking for grounds or shorted coils.
To test for grounds, use a 12 volt test lamp and check between each
segment of the commutator and the shaft. Don't touch probes to the
commutator brush surfaces; this will burn the smooth surfaces .
A growler is necessary to test for shorted coils. With the armature in
the growler, run a steel strip over the armature surfaces.
If
a coil is
shorted, the steel strip will become magnetized and vibrate.- Rotate
the armature slightly and repeat the test. Do this for one complete
revolution of the armature. If the armature has a short or ground,
replace
it.
If
the commutator is only dirty or discolored, clean it with very fine
sandpaper. Blow the sand out of the motor after cleaning. If, however,
it is scored, rough or worn, turn it down in a lathe.
3.6.4.2 Field Coils. - Using a 120-volt test lamp and probes, check
the field coils for grounding to the motor frame or open circuit. Inspect
all connections to be sure they are properly clinched and soldered.
Inspect the insulation for evidences of damage. The only way to check
for field coil shorts is to use the test in sect 3.6.2.
3.6.4.3 Bearings. - If either the front or rear bearings show exces ­
''/
sive wear, replace them. Drive the old bearings out, and using an ar ­
,
bor press and the proper arbor, press new bearings into place.
3.6.4.4 Brushes. - Check the brushes for wear or improper seating.
They should slide freely in their holders. Check the brush spring ten­
sion with a spring scale. To change spring tension, twist the spring
at the holder with long nosed pliers.
If
brushes are excessively worn, replace them.
Some brushes are soldered to the field coil lead. Unsolder the lead
and open the loop in the field coil lead. Insert the new brush pIgtail
completely into the loop and clinch before resoldering. A good solder ­
ing job is necessary to insure good contact and low voltage drop
across the connection.