NORMAL ELECTRODE CONDITION
Insulator tip gray, tan or light brown. Few combustion
deposits. Electrodes not burned or eroded. Proper
type heat range plug for engine and
service. Spark
plug should be cleaned
regapped and tested before
reinstallation.
NORMAL WORN-OUT CONDITION
Electrodes eroded by high-voltage sparking and
by
corrosive gases formed during combustion to less
than
I12
original thickness. More voltage needed to
fire spark plugs
-
often more than ignition system can
produce. Discard and replace with new spark plugs.
SEVERE WORN-OUT CONDITION
Excessively eroded center and ground electrodes
plus extensive necking of fine wire ground electrodes
indicate abnormal engine power or plugs long over-
due for replacement. Check fuel metering and magneto
timing. Discard spark plugs and check heat range
-
before installing
new
ones.
ELECTRODE WEAR PATTERNS
Constant polarity occurs with even-numbered cylinder
magnetos. One plugs fires with positive polarity, causing
excessive
groundelectrode wear, while the next plug fires
negatively, causing excessive center electrode wear. To
equalize this, rotate as indicated in above figure
12-2.
FIGURE 72-40-13A SPARK PLUGS
FIGURE
7240-13B. REVERSE SPARK PLUG PROCEDURE
72-40-08
REVISED
OCT
97
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