Plymouth Valiant V-100 1965 Service – Technical Manual page 205

IGNITION SYSTEM 8-61
above 50-60 mph. The shiny deposit (Fig.
7)
may be
yellow or tan in color. It usually suggests that tem-
peratures have suddenly risen during a hard accelera-
tion. As a result normal deposits do not get a chance
to fluff off the plug
.
. . instead they melt and form
a conductive coating.
If this continues to reoccur,
suggest a colder heat range and regular spark plug
cleanings
.
Scavenger Deposits
Fuel scavenger deposits, (Fig. 8 ) may be white or
yellow in color. They may
appear
to be bad, but
this is a
normal
appearance with certain branded
fuels. Such materials are designed to change the chem-
ical nature of deposits to lessen misfire tendencies.
Notice that accumulation on the ground electrode and
shell areas may be unusually heavy, but the material
is easily flaked off. Such plugs can be considered nor-
mal in condition, and can be cleaned with standard
procedures.
Overheating
Overheating, (Fig.
9) is
indicated by a white or light
gray insulator which appears "blistered." Electrode
gap wear rate will be considerable in excess of .001"
/lo00 miles. This suggests that a cooler heat range
should be used
. . .
however, over-advanced ignition
timing, detonation and cooling system stoppages can
also overheat the
correct
spark plug heat ranges.
Turbulence Burning
Turbulence burning, (Fig.
10)
causes electrodes to
wear away on one side. This is the result of normal
turbulence patterns in the combustion chambers of
certain engines. It can be ignored if normal plug
life
is
being obtained.
If
gap growth appears excessive,
review the corrective measures suggested under
over-
heating.
Initial Pre-Ignition Damage
Initial pre-ignition damage may be caused by exces-
sive temperatures, (Fig.
11) this
produces melting of
the center electrode and, somewhat later, the ground
electrode. Remember that the spark plug
is
like an
Fig. 8-Scavenger Deposits
Fig. 9 4 v e r h e a t i n g
Fig. I L - T u r b u l e n c e Burning
f i g . 1 7 4 n i t i a l Pre-Ignition Damage
Fig. 72-Sustained Pre-Ignition Damage