Question: how to tighten ngk spark plugs?
Answer: Confirm that the thread reach of the spark plug is the right one for your engine. Remove the dirt at the gasket seal of the cylinder head. Tighten the spark plug finger-tight until the gasket reaches the cylinder head, then tighten about ½ – ⅔ turn more with a spark plug wrench. (Taper seat: About 1/16 turn more.)