Suzuki VZ1500 Owner's Manual page 114

Installation
CAUTION
A crossthreaded or overtightened
spark plug will damage the aluminum
threads of the cylinder head.
Follow the procedure below to
tighten the spark plug properly.
Carefully turn the spark plug by hand
into the threads until it is finger tight. If
the spark plug is new, tighten it with a
wrench about 1/2 turn past finger tight.
If you are reusing the old spark plug,
tighten it with a wrench about 1/8 turn
past finger tight.
CAUTION
Dirt can damage your engine if it
enters an open spark plug hole.
Cover the spark plug hole whenever
the spark plug is removed.
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