Table of Contents
Advertisement
B
THE
IGNITION
SYSTEM
OESCRJPTJON
The
distributor
is
mounted at
the
front
of
the engine
on
the
left-hand side
and
is
drhen from the front
of
the
half-speed
shaft.
The
automatic
ad,ance device
is
hou~d
in
the
distri-
butor
unn.
and it consists of a centrifugally
and
vacuum-
operated mechanism
by means
of
-..hich the
ignition
is
ad,•
aneed in
proportion
to the engine speed
and
load.
The
combined
etrecu
of
the
centrifugally
and
vacuum-
operated timing controls give added
efficienc:y over the
full
operating
range
of
the
engine, with
a
corresponding
economy
in fuel
consumption.
A
micrometer
adjustment
is fiued by means
of which
fine alterations
to
the timing
can
he made to
allow
for changes in running conditions,
e.g.
state
of carbonization, change
of fuel,
etc.
Like the
rest of
the electrical equipment,
it
is wired
on
the
'positi\e earth' system.
which
results in longer
sparking
plug
life,
A
completely
sealed.
metalli~ed
paper capacitor is
filled to
the
distribUior.
This
has
the property
of
being
self-healing in
the
event of
a
breakdown.
so that
trouble
arising from this source
should
be very infrequent.
T11e high-tension pick-up brush in the
distri
butor
cover is of
composite
construction, the top portion con-
sisting
of a
resist ive compound and
the lower of softer
rarbon
to
prevent
wear taking
place
on
the
rotor
electrode.
The
resistive
portion
of
the
brush is in circuit
between
the
coil
and distributor
and gives
a
measure of radio
interference suppression. Under no circumstances
must
a short, non-resistive brush
be
used as a
replacement for
one of
the
longer, resistive
type.
Section B.l
LOCA11NG TilE CAUSE OF
UNEVF~
FlRJNG
Start
the engine
and
set
it to run
at a fairly
fast
idling
spttd.
Short-circuit each plug in
tum by
pulling
the insulator
slee\e
up the
cable
and
placing a hammer
head or the
blade
of
a
screwdriver
with
a wooden
or
insulated
handle betwt'rn the terminal and the
cylinder
head. No
difference
in
the engine performance
will
be noted when
short-circuiting the plug in the
defective cylinder.
Shorting the
other plugs
will
make
uneven running
more
pronounced.
Having
located the
cylinder
which is
a
t
fault.
stop
the
engine and remove the cable from
the
terminal of
the
sparking plug. Restart
the engine
and hold the end of
the
cable about
-A
in.
(4·8
mm.) from the
cylinder head.
If
the sparkinj! is
s trong
and
regular, the
fault probably
lies in the
sparking
plug. Remove
the
plug. clean it, and
B.2
adjust the gap to the correct
selling
(see 'GF.!'IERAL
DATA'), or alternatively tit a new plug.
U there is no
spark
or
if
it
is weak
and irregular,
examine the cable from the
sparking
plug
to
the
distri·
butor. After
a long
period of service the
insulation
may
be
Cl'llcked or
~risbcd,
in which
case
the
cable
sbould
be
renewed.
Finally, examine the <listributor moulded
cap,
wipe
the inside and outside
\\ith
a
clean
dry
cloth,
see
that
the
carbon brush moYCS freely
in its
holder, and
examille
the moulding
closely
for signs of
breakdown.
After IOO&
service it
may become
tracked-
that is, a
conducting
path
may have
formed
ber•.-oen
two
or
more
of
the
electrodes
o
r
between one of the electrodes and
scme
part
of
the
distributor in contact with the cap. Evidence
of
a tracked
cap
is
shown by
the
presence of a
thi
n,
black
line.
A
replacement
distributor
cap
must
be filled in pl:u:e
of
one that
has
become tracked.
Section
B.2
TESTING
THE
LOW-TENSION
CrRCUTT
Spring
back the
securing clips on the
distributor
and
remove the moulded cap
and rotor. If the rotor is
a
tight lit
it
can be
l~vered
off carefully with a
SC1'cwdrh·cr.
Check
that
the contacts are clean
and
free from pits,
burns, oil, or grease.
Turn
the
e
ngine
and check that the
contacts are opening
and
closing correctly and thai the
clearance is correct when the contacts are fully
opened.
Correct tbe gap if necessary
to
between ·0 14 and
-()
1
6
in. (·35 and ·40 mm.).
Disconnect
the cable at the contact
breaker
tel"'llimm
of tbe coil and at the low-tension terminal
of the
distri·
butor, and connect a test lamp between these terminals.
If
the
lamp
lights when the contacts close
and
goes
out
when the contacts open the low-tension
circuit is in
ordcr. Should the
lamp
fail to
light,
the contacU are
dirty or there
is
a broken or loose connection
in
the
low-
tension wiring. The procedure
for
isolating the fault
is
detailed in Section B.3.
Section
B.3
LOCATING
A
LOW-TENSION
CIRCUIT FAULT
Having
determined,
by testing as described
in Section
B.2,
that the
fault
lies in the low-tension
circuit. switch
on
the ignition
and turn
the engine until
the
contact
breaker points are
fully
opened.
Refer
to the wiring
diagram
and check
the
circuit
with
a voltmeter (0-20 volts) as follows.
NOTE.-
H the
ciradt
is
in
order the
re•dlna
011
tk
Toltmeter sboald be
aJII.Iroxlm•ttly 12
Tolls.
MGA CI'win Cam).
laue
l.
)2AQJ
Advertisement
Chapters
Table of Contents
