Perkins 4.99 - Starter Motor Servicing and Operation; Starter Motor Testing and S Type Drive Operation; S Type Starter Drive Maintenance

NOTE: This is applicable to a brush when half the
available wearing length has been worn away.
3. The commutator must be clean and have a polished
appearance. If necessary, clean It by pressing a
fine dry cloth agaiinst it whilst the armature is
turned by hand. If the commutator is very dirty,
moisten the cloth with petrol.
4. Keep all the electrical connections clean and tight.
06
Any which have become dirty should be cleaned
and the contacting surfaces lightly smeared with
petroleum jelly.
3. Servicing
(a) Testing in Position
If the starter motor does not operate or fails to crank
the engine when the starting button is used, switch on
the head lamps. When these are not fitted connect a
good quality 0-20 voltmeter across the battery ter-
minals, operate the starter button and watch for the
following symptoms:
1. The headlamps dim (or the voltmeter reading falls
appreciably) but the motor does not crank the
engine.
This may be caused by the starter drive pinion
being jammed in mesh with the engine flywheel.
The pinion can usually be freed by engaging a low
gear and gently rocking the engine. It is advisable
to remove the starter motor from the engine and
inspect the starter drive as described later in this
section.
Sluggish action of the starter motor may be due to a
discharged battery, check this by disconnecting the
existing cables and reconnecting the motor to a
battery known to be fully charged. If the starter
motor now functions normally then the battery
must be examined. Should the starter motor still
not function normally then it should be removed
from the engine and examined.
2. The head lamps do not dim (or the voltmeter read-
ing remain unaffected) and the motor does not
crank the engine.
ELECTRICAL EQUIPMENT-Q.7
Check first that the circuit up to the supply ter-
minal on the starter motor is in order.
If no voltage is indicated. check the circuit from
the battery to the motor via the starter switch.
Ensure that all the connections are clean and
tight. If the switch is found to be faulty fit a ser-
viceable replacement.
A normal voltage supply reaching the starter motor
terminal indicates that the starter motor has an in-
ternal fault and must be removed for examination.
If the starter motor operates but does not crank
the engine, the starier drive may require cleaning
or may have developed some other fault. In either
case the starter motor requires removal from the
engine for a full examination.
"S' TYPE STARTER DRIVE ASSEMBLY
(a) Operation
This drive incorporates a protective feature known as
the
'Run-off Helix'. The purpose of this feature is to
prevent possible damage occuring to the starter motor
through excessive torque being applied while the
pinion is in engagement, as would arise for example
in the event of an engine back-fire during starting.
Under normal conditions of engagement, axial move-
ment of the pinion is arrested when, in th'3 one direc-
tion, the first cup washer has fully compressed the re-
straining spring and is abutted hard against the second
cup washer and, in the opposite direction, the helically
screwed sleeve is pressing the thrust washer hard
against the main spring.
In the 'Run-off Helix' drive, the main spring is capable
of greater compression than is the equivalent stan-
dard 's' pattern drive spring. In addition, the trailing
faces of the pinion and helically screwed sleeve are
machined to form indented rachet recesses.
In the event of a back-fire occuring during starting,
the pinion (being able to rotate but incapable of fur-
ther axial movement) forces the heiically screwed
sleeve along the straight-splines of the starter shaft.
This further compresses the main spring and permits
axial movement of the screwed sleeve to continue until
it is clear of the interior of the pinion. At this stage,
axial movement of the screwed sleeve ceases and the
pinion, now jointly supported by the fixed sleeve and
the recessed end of the screwed sleeve, is free to be
rotated by the engine ring gear. In this way, excessive
torque is harmlessly dissipated by the ratchetting
action of the pinion and screwed sleeve against the
reaction pressure of the main spring.
The operation of a 'Run-off Helix' drive can be checked
by securing the armature and drive assembly in a vice
(using wooden vice-clamps) and applying a torque
wrench to the pinion. The rachet action must occur at
a torque of not less than 36 Ibf ft (5 kgf m).
(b) Routine Maintenance
If any difficulty is experienced with the starter motor
not meshing correctly with the flywheel, it may be that
the drive requires cleaning.
The pinion should move freely on the screwed sleeve;
if there is any dirty or other foreign matter on the
sleeve it must be washed off with paraffin.