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Ignition
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 1/2 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 ground-electrode wear, while the next plug fires
negatively, causing excessive center electrode wear. To
equalize this, rotate as indicated in Figure 10-4.
FIGURE 8-2. SPARK PLUG WEAR
8-5
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