Key to Fig 3:5
3 Contact
points
l Screwdriver
2
H.T.
cable
Before
replacing
the
plugs,
clean the threads with
a
wiÍe
brush. but do not use
this
brush on
the
electrodes.
lÍ
it is Íound
that
the
plugs
cannot be screwed in by hand,
run
a
tap down the threads in the cylinder head. Failing
a tap, use an
old sparking
plug
with crosscuts down
the
thÍeads.
Finally
tighten
with a box spanner through
half
a turn.
3:6 Testing
the
ignition
system
Primary
circuit:
To test the
primary
circuit,
loosen
the distributor cap
clips and
move
the cap to one side.
Remove
the rotor.
Turn the engine
over until
the
contact
points
close and
switch on
the ignition.
Remove
the
high-tension wire
leading
to the
centre
of
the distributor
cao. This
is the main
wire from the
ignition
coil which
supplies
the high voltage to the
d istributor.
Hold this
wire
about
j
inch from
any metallic
part
of
the engine. Open
and
close the contact
points
with
a
screwdriver, holding the screwdriver
only against the
moveable contact
point
as shown in FIG 3 :5.
A
good,
regular
spark
from
the high-tension wire to
earth means a
good primary
circuit
and
good
ignition
coil,
A weak spark, or no
spark at all
indicates trouble with
either the
primary
circuit or
igniton
coil.
Contact
points:
To test the condition
of
the ignition
contact set, turn
the
engine
over
until
the
contact
points
are open.
ReÍer
to
FIG 3
:6
and slide the screwdriver uo and down
making contact between the
moveable
point
and the
bottom
plate
of the distributor. You
are
now using the
blade
of
the
screwdriver and
the
bottom
Dlate
oÍ the
distributor as a set of contact
points.
A
good
spark
from
the
high-tension
wire to earth, after having no spark in
34
the
previous
test for the
primary
circuit, means that the
contact ooints are defective.
Condenser
(Capacitor)
:
A shorted
condenser
can be
checked
by
noting. in the
test Íor
contact
points,
described
previous
to this test,
whether
or
not the tip oÍ the screwdriver blade sparked
against the
ground
plate
as it
was
slid up and down.
No spark indicates either a shorted
condenser
or
a
break
in the
primary
circuit.
This can be
checked further
by disconnecting
the
condenser case where it is
attached
to the distributor.
Do
not
disconnect
the
condenser electrical wire.
Hold the condenser
so
that its case does not come
into
contact
with
any
metallic
part
of
the
distributor.
Repeat
the test
of moving
the
screwdriver blade up and
down
while
holding it
against
the
moveable
point.
Ensure that the contact
points
are open during this
test.
A spark at
the screwdriver tip now, which was not
present
with
the
condenser in
the
circuit,
indicates that
the condenseÍ is shorted
out.
No spark at
the
screwdriver
tip with the
condenser
out
of the
circuit
indicates that there is
an
ooen circuit some-
where in the
pÍimary
circuit.
Check the small
lead
from the
primary
terminal to the
moveable
contact
point,
as
this lead
sometimes
parts
under
constant
Ílexing
during operation.
Secondary circuit:
The secondary circuit
cannot
be tested until
the
primary
circuit
is f unctioning
correctly.
To test the secondary
circuit,
turn
the engine over
until the
contact
points
close.
Turn on the ignition.
Hold
the main
high-tension
wire
(Írom
the centre oÍ
the distributor cap)
aboLl,t
j
inch from
any
metallic
part
of
the
engine. Open and close
the contact
points
with
a
FIG 3:5 Method
of
testing the
primary
circuit
FIG 3:6
Method
of testing
the contact
points
Key to Fig 3:5
1 H.T.
cable 2
Insulator
3 Screwdrtver
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