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Best to use a torque wrench
When changing the spark plugs in our 2007 Corolla (original plugs, never been removed, 131 k miles, Mobil 1 all its life), the first few turns backing out were moderately high torque and then the rest was easy by hand with only socket and extension attached. The plugs were in excellent shape with white, dry insulators and only minor metal transfer at the electrodes (could have gone many more miles). There was only a small amount of oil on the threads of two of them, and a tiny amount of oil on one or two of the coil inserts indicating I need to change the VC gasket soon.
The plugs were replaced with same as original Toyota branded Denso SK16R11. The spec value of torque in the Toyota shop manual is 18 ft-lb (216 in-lb, 25 N-m). The plugs went in easily, finger tight, and came up hard as if seating the compression seal washers. I CAUTION anyone who tightens 1/4 turn or less after this or torques plugs on a hot engine that they are likely not seating the plug properly or may damage the head threads. Finger tight is not reliable for determining seal contact. Depending on the condition of the crush washer, the tightening process may take more than a turn. And only a properly calibrated, properly used torque wrench will tell you when you have seated the plug correctly, especially if others have messed with your spark plugs before or if you have carbon or other deposit problems. The plug spec for my 1ZZ-FE engine states 18 ft-lb. The 2ZZ-GE engine is much lower (about 12.5 ft-lb).
With a NEW PLUG (Denso SK16R11) on the 1ZZ-FE engine, after finger tight, the torque will climb to around 12 ft-lb as the washer begins to crush. This initial rise may take about a 1/4 turn. Then the torque will stay at about this value as the washer is being crushed. This crush process may take as much as a full turn. Then the torque rises quickly as the seal is finally seated. This final seating may take another 1/4 turn.
With a USED PLUG, the washer is already crushed and the torque rise to spec value may take only around a 1/4 turn total.
Suggestions for proper plug torque.
1. Use a smaller torque wrench (Not the same one you use for your lug nuts!), preferably a beam type that has a max setting of 600 in-lb, or even 250 in-lb. That way it is user calibrated and accurate in the range needed for plugs. Trying to use a 250 ft-lb click type (breakover) torque wrench is just asking for trouble and will probably result in over-torqueing.
2. Follow the suggestions that others have made to only use fingers, an extension and a plug socket (with the foam insert) to remove and start rethreading plugs. That way you are less likely to drop the plug and mess up the gap or insulator, and you can "feel" the condition of the threads to avoid cross threading.
3, In technical terms, Use Pure Couples when using a torque wrench (or any socket wrench in general). A Couple is the application of two forces in opposite directions to provide pure torque. This prevents putting a bending moment on the plug, bolt or nut which can bias the applied torque and damage the plug, bolt or nut. To apply a pure couple to the torque wrench, hold the wrench head with one hand and the handle with the other. Whatever force you apply at the handle, try to apply the same force in the opposite direction at the head. This is just common sense if you think about it.
4. Use a new plug if you can. If this is not practical, it is especially important to properly use a torque wrench and have a clean seal, seat and threads. This is because a used plug's crush washer is already crushed and, as was already pointed out, the factory thread lube is gone or not as effective. And remember, a dropped plug belongs in the garbage, never in your engine.
5. If you choose to use an anti-seize compound on the threads, I would suggest reducing the spec torque by 20%. Anything you put on the treads may get on the electrodes or insulator, especially if you use too much or put it near the end of the plug.