 Replacing
spark plugs is usually not difficult, but it is important
to use the correct grade of plug for your engine.
This is because the flow of heat into a plug is determined
by the engine design, while the flow of heat out of
the plug is
determined by the constructional details of the particular
plug. It follows that, if the plug and engine are
matched, the plug will maintain its most effective
temperature, resulting in good performance and a long
plug life, but if the plug and engine are a mismatch,
the plug will not last or perform properly, and may
even cause engine damage.
This
means that the code, which is printed on the side
of the plug, should match the brand and code shown
in the owner's manual. If the manual is not available,
or if you want to change to another brand, then consult
a spark plug chart, available at all reputable spares
outlets. Some new cars are fitted with platinum plugs,
which last a lot longer than normal plugs but
only if you're using unleaded fuel. Lead shortens
a plug's life dramatically.
Fitting
new plugs requires a certain amount of care. The leads
should be marked so you don't refit them in the wrong
position, and they should be pulled off the plugs
carefully by gripping the end fittings and not the
wire portion. The gaps are set at the factory, but
should be checked, and the material surrounding the
plug hole should be clean. Initial mating of the threads
should be done by hand to avoid getting them crossed,
or, if you have to use a tool, make sure that the
installation is not forced.
Do
not over-tighten the plugs, and install them dry or
lightly oiled. In the case of plugs with a captive
gasket, turn the tool until a first resistance is
felt, and then turn only through another 90 degrees
if the plugs are new, plus an extra 30 degrees if
the plugs have been used. If the seat is conical,
the plugs only have to be turned 15 degrees after
feeling the first resistance.
One
of the hardest- working parts in an engine is the spark
plug, so it's important to fit the correct grade at
the recommended intervals.
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