Proper torque for spark plugs

[retiredoz]

Somewhere (and now I don’t remember where ) in my stash I found an article describing the virtues of proper spark plug torque. The number I recall was 17-19 ft/lbs. Does anybody use torque wrenches for spark plugs ? What do you do with the plugs only accessible with a box or Crescent wrench ?
Given the frequency of stripped spark plug holes, maybe a ‘max torque’ number should be part and parcel of motor specs ?

[frankr]

Good question. A typical OMC motor might specify 17 1/2 – 20 1/2 foot pounds. But while I am a firm believer in using a torque wrench on many things, spark plugs are not one of them. If you are going to do it, use an inch-pound wrench. Foot pound ones just aren’t accurate enough to get it that close, unless you have a high quality one that has been recently calibrated. Besides, 20 foot pounds is right on the verge of stripping a plug in an aluminum head, especially if the threads are worn a bit. Installing a new plug, you can feel the washer crush and get tight. That’s time to quit cranking on it. Used plugs? Well you eventually will get a feel for it.

Scientifically speaking, the torque probably does affect the heat transfer. But I don’t lie awake worrying about it.

[Author]

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