Starter Motor Testing - Johnson SKEE-HORSE 25-201R Service Manual

7-14
STARTER
MOTOR
B
=
.15 VOLTS
Figure 7-38
AMMETER
TACHOMETER
Figure 7-39
~G~I
+ -
GROUND ON MOTOR
Figure 7 -40 .
e.
If
starter motor turns engine at normal cranking speed with a volt-
age reading between 9.5 volts minimum and 10.5 volts maximum,
starter motor is satisfactory. If available voltage reading at the
starter motor is low, review the following chart for probable
causes.
Starter System Voltage Drop Test
a. By making a systematic check from the positive battery terminal,
through the starting circuit and back to the negative battery termi-
nal, any component or electrical connection having excessive re-
sistance, thus causing high voltage drop and subsequent hard start-
ing, can be pinpOinted (see Figure 7-38).
b. Ground spark plug high tension leads so that engine can be cranked
without firing. Connect voltmeter and turn ignition switch to
ST ART to crank engine. NOTE: By placing voltmeter leads
against battery, solenOid, and starter motor terminals rather than
against connecting cable ends, each connection can be tested for
high resistance along with component.
c. Clean and retighten, or replace, any connection, cable, or com-
ponent having greater than speCified voltage drop.
STARTER MOTOR TESTING
The no-load test is used to determine quickly the general mechanical
and electrical condition of the starter motor. The stalled torque test is
used to determine whether or not the starter motor has sufficient torque
to crank the engine for fast starting.
N
0-
Load Test
a. Connect starter, with an ammeter in series, to a 6-volt source
(see Figure 7-39). Use a tachometer or rpm indicator to indicate
armature speed.
b. Ammeter should indicate 60 amperes maximum ; rpm indicator
should indicate 4200 rpm minimum.
If
readings are not as speci-
fied, check for binding in starter or failure of windings. NOTE: If
starter motor turns slowly, smokes after a very few seconds of
running, or gets hot instantly, stop testing. Disassemble starter
and check for shorts.
Stalled Torque Test
a. Connect a voltmeter between the starter terminal
(+)
and motor
frame (-). Using a torque wrench to stall motor armature (see
Figure 7-40), connect starter motor through an ammeter to a 12-
volt battery.
b. Voltmeter reading should be approximately 10 volts during this test.
Torque should be a minimum of 108 inch pounds or 9 foot pounds
and current should be a maximum of 405 amperes.
If
motor smokes or gets hot instantly, stop testing, disassemble
starter and check for shorts. Use only a fully charged 12-volt
battery when making stalled torque test. Obtain readings as
rapidly as possible to prevent starter overheating. Allow suf-
ficient time for starter to return to room temperature if it is
necessary. to repeat stalled torque t.est.
)
)