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Servicing


Testing in Position to Locate Fault in
Charging Circuit


1. Inspect the driving belt and adjust if necessary.


2. Check the connections on the commutator end
bracket. The larger connector carries the main
dynamo output, the smaller connector the field
current.


3. Switch off all lights and accessories, take off the
cables from the terminals of the dynamo and con-
nect the two terminals with a short length of wire.


4. Start the engine and set to run at normal idling
speed


5. Clip the negative lead of a moving coil type volt-
meter calibrated 0-20 volts, to one dynamo ter-
minal and the positive lead to a good earthing poin*
on the yoke.


6. Gradually increase the engine speed, when the
voltmeter reading should rise rapidly and without
fluctuation. Do not allow the volt meter reading to
reach 20 volts, and do not race the engine in an
attempt to increase the voltage. It is sufficient to
run the dynamo up to a speed of 1,000 rev/min. If
the voltage does not rise rapidly and without fluct-
uation the unit must be dismantled for internal ex-
amination. Excessive sparking at the commutator
in the above test indicates a defective armature
which should be replaced.


Starter Motor


Models 2M113, M45G, S12-84 and S12-85


General


This starter motor is a four-pole, four-brush earth return
machine with series-parallel connected field coils.


A solenoid-operated pre-engaged drive assembly is
carried on an extension of the armature shaft. The main
features of this type ot drive are as follows:-


a) Positive pinion engagement preventing the pinion
being thrown out of mesh whilst starting.


b) Dual-purpose plate-clutch incorporated in the drive
assembly giving over-speed and over-load protec-
tion.


c) Self-indexing pinion to ensure smooth engagement
between the pinion and the flywheel teeth before
the starter motor begins to rotate.


d) Armature braking system to ensure rapid return to
rest when the starter button is released.


Operation
On turning the starter switch, a solenoid unit mounted
on the starting motor yoke is energised and actuates
a forked lever to engage the orive pinion with the
engine flywheel. On occasions of tooth-to-tooth abut-
ment, axial movement of the pinion is arrested whilst a
helically splined sleeve in which the pinion is carried,
continues to move forward. This causes the pinion to
rotate relative to the flywheel. When the teeth become
aligned, spring pressure slides the pinion into mesh
with the flywheel.


When the pinion is properly engaged with the flywheel
teeth a pair of contacts are closed in the rear of the
unit. Closure of the contacts connects the motor to the
battery, the armature rotates and the starter pinion
commences to crank the engine.


When the engine fires and the starter switch is re-
leased, the solenoid unit is de-energised and the
spring-loaded plunger withdraws the starter pinion to
its out-of-mesh position. The armature is brought rapid-
ly to rest by the centrifugal action of a pair of spring-
loaded brake shoes bearing against a brake drum
inside the intermediate bracket.


Provision is made to ensure that in the case of the
pinion jamming in mesh (this may occur with an
engine which fails to start) there is sufficient slack in
the engagement lever-to-solenoid plunger linkage to
permit the solenoid switch contacts to open.


In the event of the drive remaining in mesh with the
flywheel after the engine has run up to speed the
starrer motor armature is protected from overspeeding
by the plate clutch assembly. This clutch allows
totque to be transmitted from the starter motor to the
engine bu: not in the reverse direction which is free
running.


The clutch is set to slip at between two and three
times normal starting torque, thus providing overload
protection for the starter motor. Back-firing is a typical
example of overloading.


Routine Maintenance


The starter motor requires no routine maintenance
beyond the occasional inspection of the electrical
connection which must be clean and tight, the brush
gear, and the commutator.


After the starter motor has been in service for some
time, remove the starter motor from the engine and
submit it to a thorough bench inspection.


1. Brush wear (this is a fair indication of the amount
of work done). Renew brushes worn to, or approch-
ing, 5/16 in (7,9 mm) in length.


2. Brush spring tension. Correct tension is 30-40 oz
(0,85-1,13 kg). Renew springs if tension has
dropped below 25 oz (0,71 kg).


3. Skim commutator if it is pitted or badly worn.


4. Check bearings for excessive side play of armature
shaft.


5. Check pinion movement.


6. Clean and lubricate the indented bearing inside
the pinion sleeve using Shell SB2628 grease for
temperate and cold climates or Shell Retinex for
hot climates.


7. Clean and lubricate the indented bronze bearing
in the intermediate bracket. Use Ragosine 'Molypad'
Molybdenised non-creep oil for this purpose.


Servicing
Testing in Position


Switch on the lamps. If the vehicle is not equipped
with lighting, then connect a 0-20 voltmeter across the
battery terminals before proceeding. Operate the starter
control and watch for the following symptoms:-


1. The lamps dim (or voltmeter reading drops to
about 6 volts, and the motor does not crank the
engine).


Check battery (must be at least half-charged) and
battery lugs, (clean and a good earth connection).
Check by hand-cranking that the engine Is not
abnormally stiff.

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