------
.---THE
IGNITION
EQUIPMENT
C
Whenever
possible,
sparking
plugs should be
cleaned in a special plug
cleaner
of
the
type
supplied
by
the
plug
manufacturer.
Oily
plugs should be
washed
with
petrol
first. A
compressed
air Jet should
then
be used
to
remove
any abrasive from
the
Interior
of
the
plug body and
the
insulator.
If a plug
cleaner
is
not
available, a
wire
brush
is
the
best
substitute.
This
should
also be used
to
clean any accumulation of
carbon
from
the
threads.
The
thread
portion
of
the
plug body is
often
neglected
when
cleaning
owing
to
the
fact
that
it is
not
generally realised
that,
like
the
Fig. c.s.
Here
is shown a plug
with
a
cracked
insulator.
gaskets,
the
threads
are
an
important
means of heat
dissipation and
that
when
they
are
coated
with
carbon
It
retards
the
flow
of
heat
from
the
plug and leads
to
overheating.
Cleaning
the
thread
will also facilitate refitting
of
the
plug and avoid
the
use
of
unnecessary force on
the
plug
spanner.
Having
ensured
that
the
plug is
thoroughly
clean
and
stiII serviceable,
the
electrodes
sh0 uId be
reset.
A
combination
gauge and
setting
tool
produced
by
the
makers
of
Champion
sparking
plugs
greatly
facilitates
the
correct
and easy
setting
of
the
sparking
plug
points,
but
care
should be
taken
to
avoid a false reading
through
distortion
of
the
points
by burning.
When
resetting
the
points,
the
side
electrode
only
should be
adjusted
to
give
the
correct
clearance.
Never
bend
the
centre
electrode.
Champion
L.IOS
or
NA.8 plugs
are
fitted as
standard
(see
page
CI),
and
their
correct
spark
gap
should
be
set
between
·020 in. and ·022 in. (,50 mm. and ·56
mm.).
Remember
that
electrode
corrosion
and
the
develop.
ment
of
oxides
at
the
gap
area
vitally affects
the
spark-
ing efficiency. The special plug
deaner
can
remove
oxides
and
deposits
from
the
insulator,
but
the
deaner
stream
does
not
always reach
this
area
with
full effect
owing
to
its location, and
cannot
necessarily
deal
with
corrosion
effectively as
this
sometimes
requires
too
strong
a blast
for
proper
removal.
When
piugs
appear
worthy
of
fu
rthe
r use it is good
practice
to
dress
the
gap
area
on
both
centre
and side
electrodes
with
a small file
before
resetting
them
to
F M.G. Midget {Series" TD "J. Issue 2 (E)
79345-1/53
the
correct
gap. The i
nte
nse
heat,
p
ressu
res,
exp
loslon
shock, and electrical and chemical
action
to
which
the
plugs
are
submitted
during
miles
of
service
are
so
Intense
that
the
molecular
structure
of
the
metal of
the
points is
eventually
affected. Plugs
then
reach a
worn-out
condition
where
resetting
of
the
points no
longer
serves
a useful
purpose
and
where
plug replace-
ment
is called for. Every 12,000 miles (20000 km.) new
piugs
should,
therefore,
be
fitted.
Before replacing a used plug in
the
engine,
test
it
for
correct
functioning
under
air
pressure in a plug
tester,
follow! ng
out
th e i
nstru
ctl
ons
issued by
the
makers
of
the
tester.
Generally
speaking, a plug may
be
considered
satisfactory
for
fu
rther
service
if it
sparks
continuously
under
a
pressure
of
100
lb.jsq,
in.
(l
kg·/cm.
2
)
wlth
the
gap
between
the
points
set
at
·022 in.
(-56
mm.). It is essential
that
the
plug points
then
be
reset
to
the
smaller
gap of ·020 in. (·50
mm.)
before
the
plug Is
refitted
to
the
engine.
While
the
plug is
under
pressure
In
the
tester
it
should be inspected
for
leakage by applying oil
round
the
terminal
and
insulator.
Leakage is indicated by
the
production
of
air
bubbles,
the
intensity
of
which give an indication
of
the
degree
of leakage.
Fig. C,6.
Adjustmenu
to
the spark plug gap should be made only by
bending
the
side wi re, prefe rably by us;ng a prope r settlng
tool
such
as
the"
Champion"
setting
tool
here
illustrated.
The
leaking gases have a
"blow-torch"
effect
when
the
engine is running which rapid Iy raises
the
tem-
perature
of
the
plug
to
above
its
heat
range,
thus
producing
overheating,
pre-ignition, and rapid elec-
trode
destruction.
The
top
half
of
the
Insulator is also
frequently
responsible
for
poor
plug
performance
due
to
the
foHowing
faults:
splashes, accumulation
of
dirt
or
dust,
cracked insulators (caused by a slipping
spanner),
over-
tightness
of
the
terminals.
Examine
for
a
cracked
insulator
at
the
shoulder
and
the
terminal
post
and
remove
any accumulations
of
dirt
and
dust.
c.s
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