Service Sheet No. 1051 (cont.)
Bench Testing
(i) Measuring the Light Running Current.
With the starting motor clamped in a vice and using two fully charged, series-connected, 6-volt 12 amp.hr.
batteries, check the light running current and compare with the value given in paragraph on Performance Data.
Look for excessive arcing at the commutator and, if necessary, remedy. Excessive arcing may be due to
faults outlined in Fault Diagnosis 7 and 8.
(ii) Measuring Lock Torque and Lock Current.
Carry out a torque test and compare with the values given in paragraph on Performance Data. If a
constant voltage supply is used, it is important to adjust this to be 6.5 volts at the starter terminal when
testing.
(iii) Fault Diagnosis.
An indication of the nature of the fault, or faults, may be deduced from the results of the light running and
lock torque tests.
Symptom
Probable Fault
1. Speed, torque and current consumption
None.
correct.
2. Speed, torque and current consumption low.
3. Speed and torque low, current consumption
high.
Speed and current consumption high, torque
low.
Armature does not rotate, no current con-
sumption.
Armature does not rotate, high current con-
sumption.
Excessive brush movement causing arcing at
commutator.
8. Excessive arcing at the commutator.
High resistance in brushgear, e.g., faulty con-
nections, dirty or burned commutator causing poor
brush contact.
Tight or worn bearings, bent shaft, insufficient end
play, armature fouling a pole shoe, or cracked
spigot on drive end bracket. Short-circuited
armature, earthed armature or field coils.
Short-circuited windings in the field coils.
Open-circuited armature or field coils. If the
commutator is badly burned there may be poor
contact between brushes and commutator.
Defective armature windings, sticking brushes or
dirty commutator.
4.
5.
6.
7.
Earth field coil or switch.
prevented from rotating.
Low brush spring tension,
commutator. " Thrown "
commutator.
Armature physically
worn or out of round
or high segment on
ENGAGEMENT LEVER ADJUSTMENT
With the switch firmly bolted to the yoke, fix and lock the engagement lever adjusting screw in such a
position as to provide a clearance of 0.005" to 0.010" between the pinion face (when the drive is lightly pushed
backwards to take up any slackness) and shaft jump ring when the lever reaches its ultimate engaged
Position}.
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