How Tight Should Your Spark Plugs Be?

The manufacturers of each brand have the answer –

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.

Proper Tightening Procedure

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:

With a Torque Wrench:

Please note there are slight variations in torque recommendations between spark plug manufacturers.  To find the manufacturers 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.

Without a Torque Wrench:

If a torque wrench is unavailable, finger tighten the spark plug, then use a plug wrench to tighten.

Autolite -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.  1/16 turn on plugs with a tapered Seat.

Bosch – 1/4 turn on plugs with a gasket.  1/16 turn on plugs with a tapered Seat.

Champion – 3/8-5/8 turn on plugs with a gasket.  1/16 turn on plugs with a tapered Seat.

Denso – 1/4-1/2 turn on plugs with a gasket.  1/8 turn on plugs with a tapered Seat.

E3 – For spark plugs with a gasket: 1/2 turn on 10mm plugs, 3/8-1/2 turn on 12mm plugs, 1/2-3/4 turn on 14mm plugs.  1/16 turn on plugs with a tapered Seat.

NGK -1/2-2/3 turn on plugs with a gasket.  1/12-1/8 turn on plugs with a tapered Seat.

PLEASE NOTE:

• Torque recommendations are for spark plugs with new gaskets.
• If using anti-seize compound, use sparingly and reduce torque by 30%.
• Each spark plug manufacturer has created their recommendations based on the general consensus of most engine manufactures.  In the case of a discrepancy between the plug manufacturer and engine manufacturers recommendations, always default to the engine manufacturer.