Honda GCV520 Owner's Manual page 26

4. Check that the spark plug washer is in good condition and
thread the spark plug in by hand to prevent cross-threading.
5. After the spark plug is seated, tighten with a spark plug wrench
to compress the washer.
When installing a new spark plug, tighten 1/2 turn after the spark
plug seats to compress the washer. When reinstalling a used spark
plug, tighten 1/8 1/4 turn after the spark plug seats to compress
the washer.
The spark plugs must be securely tightened. Improperly tightened
spark plugs can become very hot and may damage the engine.
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