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l-22
GENERALINFORMATIONAND
MAINTENANCE
tears. If the boot is damaged, it should be replaced
trode is to the block's cooling passages) the cooler it
your driving is long distance, high speed travel, use a
immediately. Please refer to Section 7 for procedures. will operate. A plug that absorbs little heat and re-
colder plug; if most of your driving is stop and go,
mains too cool will quickly accumulate deposits of
use a hotter plug. Original equipment plugs are gen-
oil and carbon since it is not hot enough to burn
erally a good compromise between the 2 styles and
them off. This leads to plug fouling and consequently most people never have the need to change their
to misfiring. A plug that absorbs too much heat will
plugs from the factory-recommended
heat range.
ti See Figure 88
have no deposits but, due to the excessive heat, the
,electrodes will burn away quickly and might possibly
REMOVAL &INSTALLATION
A typical spark plug consists of a metal shell sur-
lead to preignition or other ignition problems. Preig-
rounding a ceramic insulator. A metal electrode ex-
nition takes place when plug tips get so hot that they
ti See Figures 90 thru 95
tends downward through the center of the insulator
glow sufficiently to ignite the air/fuel mixture before
and protrudes a small distance. Located at the end of
the actual spark occurs. This early ignition will usu-
A set of spark plugs usually requires replacement
the plug and attached to the side of the outer metal
ally cause a pinging during low speeds and heavy
after about 20,000-30,000 miles (32,000-48,000
shell is the side electrode. The side electrode bends
loads.
km), depending on your style of driving. In normal
in at a 90" angle so that its tip is just past and paral-
The general rule of thumb for choosing the correct
operation plug gap increases about 0.001 in.
lel to the tio of the center electrode. The distance be-
heat range when picking a spark plug is: if most of
(0.025mrn) for every 2,500 miles (4,000 km). As the
tween these two electrodes (measured in thousandths
of an inch or hundredths of a millimeter) is called the
spark piug gap.
The spark plug does not produce a spark, but in-
steed provides a gap across which the current can
arc. The coil produces anywhere from 20,000 to
50,000 volts (depending on the type and application)
which travels through the wires to the spark plugs.
The current passes along the center electrode and
jumps the gap to the side electrode, and in doing so,
ignites the air/fuel mixture in the combustion charn-
ber.
SPARKPLUG HEATRANGE
ti See Figure 89
Spark plug heat range is the ability of the plug to
dissipate heat. The longer the insulator (or the farther
INSULATOR
CRACKS
OFTEN
OCCUR
HERE
SIDE ELECTRODE
ENTER
ELECTRODE:
(SEND
TO ADJUST
GAP)
FILE FLAT WHEN
ADJUSTING
GAP;
DO NOT BEND
Fig. 88 Cross-section of a spark plug
it extends into the engine), the hotter the plug will
operate; the shorter the insulator (the closer the elec-
Fig. 90 Carefully twist the boot end of the
I
spark plug wire and withdraw the spark plug
wire boot from the cylinder head
Fig. 92 A locking extension such as this is
extremely helpful when removing spark
plugs that are centrally located in the cyhn-
Fig. 94 . . . then carefully withdraw the
spark plug from the engine
Fig. 91 A special spark plug socket with a
rubber insert is required to remove the
spark plugs. Typically the spark plugs re-
quire a Ya spark plug socket
Fig, 93 Using the appropriate sized spark
plug socket, necessary extensions and drive
tools, loosen the spark plug . . .
93151ptxl
Fig. 95 After removing the plug from the en-
gine, inspect it using the spark plug condi-
tion chart in this section to determine the
running condition of your engine
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