Use a torque wrench to tighten the spark plug to a spec of 156 in-lbs (13 ft-lbs).

If a torque wrench is unavailable, tighten the spark plugs by hand, and finish with a 1/4-1/2 turn using a socket wrench until snug.

Do not over-tighten the spark plugs, as the threads may strip out of the soft aluminum cylinder head.