Chevrolet 1963 Corvette, Руководство по ремонту и настройке, Страница: 49 / 346

44 TUNE-UP AND PERFORMANCE MAINTENANCE
casion to change their plugs from the factory-
recommended heat range.
REPLACING SPARK PLUGS
Normally, a set of spark plugs requires re-
placement about every 10,000 miles on cars
with conventional ignition systems (incl.
Transistorized) and 20,000-30,000 miles on
cars equipped with an H.E.I. (High Energy
Ignition) system. Some earlier high perfor-
mance engines may require more frequent
plug changes, especially if idled or operated
at low rpm's for extended periods. Any vehi-
cle which is subjected to severe conditions
will need more frequent plug replacement.
In normal operation, plug gap increases
about 0.001 in. for every 1,000-2,500 miles.
As the gap increases, the plug's voltage re-
quirement also increases. It requires a greater
voltage to jump the wider gap and about two
to three times as much voltage to fire a plug
at high speeds than at idle.
When you're removing spark plugs, you
should work on one at a time. Don't start by
removing the plug wires all at once, because
unless you number tiiem, they may become
mixed up. Take a minute before you begin
and number the wires with tape. The best
location for numbering is near where the
wires come out of the cap.
1. Remove the radio interference shields
which cover the spark plugs and wires (in
some models).
2. Twist the spark plug boot and remove
the boot and wire from the plug. Do not pull
on the wire itself as diis will ruin the wire.
3. If possible, use a brush or rag to clean
the area around the spark plug. Make sure
that all the dirt is removed so that none will
enter the cylinder after the plug is removed.
4. Remove the spark plug using the proper
size socket. (
13
/ie in. through 1971, % in. 1972
and later.) Turn the socket counterclockwise
to remove the plug. If the engine has alumi-
num cylinder heads, be extremely careful
when removing the plugs. If any plug turns
with difficulty, spray a penetrating lubricant
(Liquid Wrench, WD-40, etc.) around the
plug threads and turn the plug back in. Wait
a couple of minutes for the oil to work its way
through the threads and then "nurse" the plug
out about
V-t turn at a time. Be sure to hold
the socket straight on the plug to avoid
breaking the plug, or rounding off the hex on
the plug.
5. Once the plug is out, check it against
die plugs shown in chapter 11 to determine
engine condition. This is crucial since plug
readings are vital signs of engine condition.
6. Use a round wire feeler gauge to check
die plug gap. The correct size gauge should
pass through the electrode gap with a slight
drag. If you're in doubt, try one size smaller,
and one larger. The smaller gauge should go
through easily while the larger one shouldn't
go through at all. If the gap is incorrect, use
the electrode bending tool on the end of the
gauge to adjust the gap. When adjusting the
gap, always bend the side electrode. The
center electrode is non-adjustable.
7. If die engine has cast-iron heads, squirt
a DROP of penetrating oil onto die plug
threads and install the plug. If the engine has
aluminum heads, apply a small amount of anti-
sieze compound to die plug threads and care
fully install the plugs. Turn the plugs in by
hand until diey are snug.
8. When the plug is finger tight, tighten it
with a wrench.
9. Install die plug boot firmly over the
plug. Proceed to the next plug.
CHECKING AND REPLACING SPARK
PLUG CABLES
Visually inspect the spark plug cables for
burns, cuts, or breaks in die insulation. Check
die spark plug boots and die nipples on die
distributor cap and coil. Replace any dam-
aged wiring. If no physical damage is ob-
vious, the wires can be checked widi an
ohmmeter for excessive resistance. (See die
tune-up and troubleshooting section.)
When installing a new set of spark plug ca-
bles, replace the cables one at a time so there
will be no mixup. Start by replacing the long-
est cable first. Install die boot firmly over die
spark plug. Route die wire exacdy die same
as the original. Insert the distributor end of
Check the gap with a round wire gauge