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8-60
IGNITION SYSTEM
Fig. 3-Wet
Fouling
drowned in excess oil. In an old engine, suspect worn
rings or excessive cylinder wear. In O W engines,
too much oil may be coming in past the valve guides.
Use of a hotter plug may relieve such fouling, but
plugs can't take the place of needed engine overhaul.
NOTE:
Remember that "break-in" fouling of new
engines may occur before normal oil control is
achieved. In new or recently overhauled jobs, such
fouling plugs can
be cleaned and reinstalled.
Splashed Fouling
Splashed fouling, (Fig.
4)
may sometimes occur aft-
er a longdelayed tune-up. Here, deposits accumulated
after a long period of misfiring may be suddenly loos-
ened when normal combustion temperatures are re-
stored upon installation of new plugs. During a high
Fig. 4-Splashed
Fouling
speed run, these materials shedding off the combus-
tion chamber are thrown against the hot insulator sur-
face. If they happen to short out the plug, they can be
removed with regular cleaning techniques. The plugs
can then be reinstalled with good results
as
the en-
gine has scavenged itself.
Core Bridging
Core bridging, (Fig.
5)
will be encountered only
rarely in automotive engines. It's usually due to the
same conditions described under splashed deposits.
In this case, a chunk of deposit was thrown off the
piston and formed a bridge between the insulator
and shell. Result: A "dead short." Such evidence of ex-
cessive combustion chamber deposits will be most
common where oil control is poor
. . .
or where vehi-
cles are usually driven in slow speed, start-stop serv-
ice. In such instances, it usually pays to physically re-
move accumulated deposits from the engine.
Gap Bridging
Gap bridging, (Fig.
6)
i s
also relatively rare in auto-
motive engines. It also may
be
traced to flying de-
posits in the combustion chamber. In a few cases,
fluffy deposits may accumulate on the plugs during in-
town driving; when the engine is suddenly put un-
der high load, this material can melt and bridge the
gap.
High Speed Glazing
High speed glazing may cause misfiring at speeds
Fig. &Gap
Bridging
Fig. 5-Core
Bridging
Fig. 7-High
Speed Glazing
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