MG MGB User Manual

THE ELECTRICAL
SYSTEM
N
19.
Check
the
brush
spring
pressure.
Each
spring
should
exert
a
minimum
of 36
02.
(1.02
kg.)
with
a
new
(full-length) brush
in
position.
COMMUTATOR
20.
21.
The
commutator
should be
burnished, free
of
pits
or
burned
spots,
and
can
be
cleaned
with
a
petrol-moistened
cloth. If this cleaning
is
ineffective,
spin
the
armature
and
polish the
commutator
with
■ne
glass-paper, removing
all abrasive
dust with
a
dry
air
blast.
In
the
case
of
a
badly
worn
commutator, mount
the
armature
between
centres
in
a
lathe and
rotate
it
at
high speed.
Take
a
light
cut
with
a
very
sharp tool
and
do
not
remove
more
metal than
is
necessary
to
clean
the
commutator.
Finally,
polish with
very
fine
glass-paper.
The
insulators between the
commutator
segments
must
not
be
undercut.
ARMATURE
22.
23.
24.
Examine
the
armature
for conductors which have
lifted from the
commutator
risers.
This would indicate
overspeeding and the drive
clutch should be checked
(see
28).
Check
for
signs
of the
armature
fouling the pole shoes
indicating
a
distorted
armature
shaft
or worn
bearings
(see
29
and
30).
Do
not attempt
to
machine the
armature
core or
to true
a
distorted
shaft;
a
damaged
armature must
be renewed.
To
make
a
thorough
check
on
the condition
of
the
armature
it
should be tested
on
a
‘growler’. The
armature
insulation
can
be checked by
means
of
a
110-volt A.C.
test
lamp connected between each
commutator
segment
in
turn
and the
armature
shaft.
The
test
lamp
should
not
light.
FIELD COILS
25.
MGB.
Test
the ■eld coils for
continuity.
Ensure that both
brushes
and their
■exible
connectors
are
clear of the
yoke and
connect
a
12-volt
test
lamp and battery
between the cable
connection
to
‘STA’
and
each of
the ■eld coil brushes
in
turn.
If the lamp does
not
light,
an open
circuit in
the ■eld
coil
is
indicated and
they
should be renewed
as
follows:
a.
Using
a
wheel-operated screwdriver,
unscrew
the
four
pole-shoe
retaining
screws.
b. Withdraw the inter-coil
connector
insulating
piece
and
remove
the pole shoes and coils from
the
yoke.
0.
Fit
new
coils
to
the pole shoes and
position
them
inside the yoke. Make
sure
that the coil
taping is
not
trapped between the pole shoes
and
the
yoke, then lightly tighten the pole-shoe
retaining
screws.
d. Fit the insulator
to
the ■eld coil
terminal and
position
the inter-coil
connection
insulator inside
the yoke. Hold the pole shoes
in position
with
a
pole-shoe
expander and
tighten the
retaining
screws
with
a
wheel-operated
screwdriver.
Issue
8.
82448
26. Test the
■eld
coils
for insulation from the yoke.
Ensure that both
brushes and their ■exible
connectors
are
clear
of
the yoke
and
connect
a
110-volt
A
C.
test-lamp
between
the
terminal
post
and the
yoke.
If
the lamp lights, earthing
of
the
■eld
coils
is
indicated
and they should
be
renewed
as
described
in
25
a
to
d.
COMMUTATOR END
BRACKET
27.
Clean all
traces
of brush deposit
from the
commutator
end bracket and
connect
a
110-volt A.C.
test
lamp
between the
end
bracket
and each insulated
brush
box
in
turn.
If the lamp
lights, faulty
insulation
is
indicated and the
commutator
end bracket
should
be
renewed.
DRIVE CLUTCH
28.
Check the
operation
of the
drive clutch.
It
should
provide
instantaneous
take-up of the
drive
in
one
direction,
yet rotate
easily and smoothly
in
the
opposite
direction.
It
should
also
move
freely
on
the
armature
shaft
splines without
any
roughness
or
tendency
to
bind.
BEARINGS
29.
30.
Renew
the
bearings which
are worn
to
such
an
extent
that they
allow
excessive
side-play of the
armature
shaft.
Remove the bearing from the
commutator
end
bracket by screwing
a
tap
squarely
into
the bearing
and
withdrawing
the bearing with the
tap.
The
drive end
bracket
bearing
can
be pressed
out.
Press
the
new
bearings
into position using
a
shouldered
highly
polished
mandrel .0005
in.
(0.13
mm.)
larger
in
diameter than the
shaft which will
run
in
the bearing.
NOTE.— The
commutator
and drive end
bracket
bearings
are porous
bronze and should
be immersed
in
clean
engine
oil
for
24 hours before ■tting.
In
an
emergency
this period
may
be
reduced by
maintaining
the oil
at
a
temperature
of
100°C.
(212°F.)
for
two
hours
and allowing the
oil
to
cool before
removing
the
bearing. Porous
bronze bushes should
not
be
reamed,
as
the
porosity
of
the bush
would be impaired.
Reassembling
31.
During
reassembly lubricate
all
moving
parts
with
Shell
Retinax
A
grease, or
an
equivalent.
32.
Reassemble the
starter motor
by
reversing
the
procedure
in
6
to
16.
33. Set
the
pinion
travel
as
follows:
a.
Connect
a
6-volt
supply,
with
a
switch
in
circuit,
between the small unmarked solenoid
terminal
and earth. The period
of
energization
should
be
kept
as
brief
as
possible
to
avoid overheating the
series
winding.
N35

MG MGB Specifications

General

Brand	MG
Model	MGB
Category	Automobile
Language	English