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N
THE ELECfRICAL EQUIPMENT
Commutator
A commutator in good condition will
be smooth
and
free
from
pits and burned
spots.
Clean the commutator
with a cloth moistened with petrol.
If
this is ineffective,
carefully polish with a strip of fine glass-paper whHe
rotating the armature. To remedy
a badly
worn com-
mutator
dismantle
the
starter drive as described
above
and
remove the
a rmature from
the
end bracket. Now
mount
the
armature in a lathe, rotate it at a
high
speed,
and ta ke a light
cut
with a very sharp tool.
Do
not
remove a ny more metal than is
absolutely
necessary,
and
finally polish with
very fine glass-paper.
The m ica on the
starte,
r
commutator
must
not
be
uodercot.
Field
coils
The
field
coils can be tested for an open circuit by
connecting a 12-volt
battery,
having
a 12-volt bulb in
one of
the
leads,
to the tapping
point of
the
field coils
to which the
brushes
are connected and
the
field terminal
post. If the lamp does not light there is an open
circuit
in the wiring of the field coils.
Lighting of the lamp
does
not necessarily
mean
that
the
field
coils are in order, as it
is
possible that one of
them
may
be earthed to a pole-shoe or to the yoke
This
may
be checked by removing the
lead from the
brush connector and holding it
on
a
clean
part
of
the
starter yoke. Should the
bulb
now light,
it
indicates that
the field
coils
a re earthed.
Should the above testS
indicate
that the fault
lies
in
the field
coils,
they
must
be renewed. When renewing
field
coils
carry out
the
procedure
detailed for
the
dynamo
(Section N.5).
Armature
Examination of the armature will
in
many
cases reveal
the cause of
failure,
e.g. conductors lifted from
the
com-
mutator due to the starter being engaged while the engine
is
running and causing the armature to be rotated at an
excessive
speed.
A
damaged
armature must in all cases
be renewed-no attempt
should
be
made
to
machine
the
armature
core
or to true
a distorted armature
shaft.
Bearings
(
coiiiJIIlltator encl)
ås which
are
worn
to
such an
extent
that they
will
allow excessive
side-play o
f
the
armature
shaft must
be renewed.
To
renew the
bearing bush,
proceed as
follows: press
the
new bearing
bush
into the end
bracket.
using a shouldered mandrel of
the
same diameter
as the
shaft which is to lit in the bearing.
The
bearing bush
is
of
the
porous
phosphor-bronze
type, and
before
fitting,
new
IMisbes
sbould
be allowed to
stancl
completely
immersed
for
24
hours ill
thin
engine oil
in
order to
fill
tbc pores
or the
bush with lubriault.
N.IO
REGULATOR
CUT-
OUT
REG
U
LATOR A
N
D
CUT-
O
UT
FAAlott
•
•
S.
FI ELD
Q
.::?"'
AESISTANC[
-=:......::1
~
SHUNT
~
C
O
IL
~
~;
(;§'
'-=-
""
~T
APPED
""\
SER
I
ES
I
COfl
..
-'
A
I,·
A
;~
F;
··
D~
E
..
-
.. __
........
_/·, __
j
"-=-''
CON TROL
BOX
Fig. N .S
j
I
J~
~~
~
SHUNT
c5
CO il.
~
'""'
~-
SERIES.
COI
L
!
487
6
The internal wiring and connections of the regulator
and cut-cut
Reassembly
The
reassembly
of
the
starter
is
a reversal
of
the
operations
described in this
Section.
Section
N.9
CONTROL BOX
Description
The control box
contains
two
units-a voltage
regu-
lator
and a cut-out.
Although
combined structurally, the
regulator a
nd
cut-out are electrically separate (see
Fig.
N.5).
Both
are
accurately adjusted
d
uring manufacture, and
the
cover
protecting them
should not be
removed
unnecessarily.
Cable
connections
are
secured
by
grub-screw-type
terminals.
Regulator
The
regulator is set
to
maintain the
dynamo
output
between
close limits
at
all
speeds above the regulating
point. the field strength being controlled
by
the
auto-
matic
insertion and withdrawal of a resistance in the
dynamo field
circuit.
When the
dynamo output
reaches
a
predetermined value the magnetic flux in
the
regulator
core,
induced
by
the shunt or voltage winding, becomes
sufficiently strong to attract the armature to the
core.
This causes the contacts to
open,
thereby
inserting
the
resistance
in
the dynamo field circuit.
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