Yamaha GRIZZLY Ultramatic YFM660FP Owner's Manual page 144

Tightening torque:
Spark plug:
17.5 Nm (1.75 m·kgf, 12.5 ft·lb)
NOTE:
_
If a torque wrench is not available when you
are installing a spark plug, a good estimate of
the correct torque is 1/4 to 1/2 turn past finger
tight. Have the spark plug tightened to the
specified torque as soon as possible.
_
4. Install the spark plug cap.
5. Install the panel.
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