ENGINE
The important thing is for the petrol
means of the copper gasket between
consumption to
be
improved. If plugs
the plug and the cylinder head. Plugs
show suitabilityfor further use, proceed
not down tight
can
be easily over-
to clean and test. heated, throwing them out of the
proper heat range, causing pre-ignition,
In preparing for cleaning, remove plug short plug life and bringing about so-
gaskets, and in doing so ascertain their called
"
pinking." Don't tighten plugs
too much-but be reasonably sure a
Fig.
38
Sparking
Plugs in
a
tray
ready for
comparison.
condition. Note the gaskets illustrated
in Fig.
41.
Upper left shows a gasket
not properly compressed.
A
large pro-
portion of the heat from the insulator
is dissipated to the cylinder head by
Fig.
39
Oil
fouling
indicated
by
a
wet
shiny
black
deposit
on
the
Insulator.
good seal is made between plug and
cylinder head. Lower left shows a
gasket on which the plug was pulled
down too tight, or had been too long
iq
service. Note the distorted condition.
Note evidence of blow-by, also a
cause of plug over-heating and re-
sulting dangers. Upper right shows a
reasonably compressed gasket giving
the plug adequate seal and a good path
for heat dissipation.
All
may
be
mm-
pared
with
the new gasket, at lower
Fig.
40
Petrol fouling indicated
by
a
dry
fluffy
black
deposit on
the
Insulator.
right.
If
gaskets are at all questionable
they should
be
replaced by new gaskets.
(e)
Occasionally a blistered insulator or
baldy burned electrode may be noted
when examining plugs (Fig.
42).
If
the plug is the
type
normally recom-
mended for the engine and was cor-
rectly installed,
i.e.?
down tight on the
gasket-the condinon may have been
brought about by a
very
"
lean
"
mixture, or overheated engine. It is
well
to remember that
plugs
operating
in
the condition
described
above
are
often the
cause
of poor engine per-
fonnana and amalragant
petrol
an-
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