Honda GC135 Owner's Manual page 34

SERVICING YOUR ENGINE
6. After the spark plug seats, tighten with a 13/16-inch spark plug
wrench to compress the washer.
If reinstalling the used
spark plug, tighten 1/8-1/4 turn after the
spark plug seats.
If installing a new spark plug, tighten 1/2 turn after the spark plug
seats.
A
loose sparkplug can overheat and damage the engine.
Overtightening the spark plug can damage the threads in the
cylinder head.
7. Attach the spark plug cap.
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