It is essential to tighten a spark plug to the specified turning angle or torque setting as torque directly impacts a spark plugs ability to remove heat from the combustion chamber. Over tightening can cause damage to the threads in the cylinder head and the threads of the spark plug, stress the spark plugs internal seal, or fracture the spark plugs insulator. Under tightening will prevent the spark plug from being properly seated on the cylinder head, resulting in insufficient contact with the head to transfer heat. Either of these would result in elevated combustion chamber temperatures, followed by pre-ignition and detonation.
Clean the spark plug threads and ensure the cylinder head is clean of debris.
Screw in the spark plug finger tight until the gasket meets the cylinder head. Then tighten the plug as specified below:
To find Autolite's recommended torque setting, please enter the spark plug number in the search box. While viewing the part detail page, click on the "specs" tab. If a recommendation has been made, it will appear under the "Specifications" heading.
If a torque wrench is unavailable, finger tighten the spark plug, then use a plug wrench to tighten.
For spark plugs with a gasket: 1/4 turn on 10mm plugs, 3/8 turn on 12mm plugs, 1/2 turn on 14mm and 18mm plugs.
For spark plugs with a tapered seat: 1/16 turn.