How tight should spark plugs be?

How tight should sparkplugs be? Ideally, you should use a torque wrench and follow the manufacturer’s torque specification. However, you can get close to this spec with the right technique. Spark plugs have crush washers to help seal the combustion chamber. If you’re reinstalling a plug, this washer has already formed to the head. Screw in the plug until it “seats,” that is, it’s finger tight. Turn the plug an additional ¼ turn.
If you’re installing a new plug, screw in the plug until it seats, then turn it an additional 2/3-3/4 turn. This crushes the washer between the plug and the head, forming a tight seal.

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