Yeah I know I'm an idiot. I wasnt thinking and just tightened them probably 3/4 turn past hand tight, didnt force anything, just kept cranking the socket until the crush washer flattened and I met resistance.

I'm pretty sure I did the same thing 70k miles ago on the last spark plug change, and those plugs has backed themselves out quite a bit over that time- when I pulled them yesterday they were not much more than hand tight.

Of course now I'm worried about the cylinder heads. Should I just leave them in or replace them just to be safe?

If anything, I'd say not tight enough.
I never torque mine, I ratchet down lightly until I feel a good 'umph', and call it good. Never had any issues.
Definitely more than hand tight + 3/4 turn, though.

If you're really worried, check with a torque wrench.

Use a torque wrench, I believe 13 ft/lbs

When you were tighting if you didn't feel any less resistance you may have dodged a bullet. What ever damage has been done is done. If you are going to replace your plugs I would go to Harbor Freight and pickup there 1/4 inch drive torque wrench they are as low as 9.99 on sale at my local HF. I have turned wrenches from the early 80's I still can not get a good feel when tighten some things like spark plugs.

Just some other facts about installing spark plugs Denso and NGK if I remember correctly they do not recommend anti seize during installation. They recommend only a light coating of oil. In addition remember torque specs maybe converted from Foot LBS to Inch LBS.

Thanks guys, I think I'll just leave em in and check with a torque wrench. I'd honestly be surprised if I damaged the threads because I didn't force anything, but going back and reading a bunch of threads about 13 ft lb torque and hand tight + 2/3 turn made me second guess myself, especially with the aluminum heads. I knew about the NGK trivalent coating and not to use anti seize so I'm safe on that at least.

That does remind me though...passenger side felt smooth and oiled, but the 3 driver side plugs felt sticky on removal and reinstall. The plugs would make it almost a full turn with almost no resistance, then stick for a crank or two, then smooth again. Almost like that trivalent coating dried up or something if thats possible. Something to keep an eye on?

Wouldn't the threads on the spark plug give out before the threads on the head?

Did you clean the spark plug recess and threads in the head?

The general idea is not to completely pancake the crush washer.
Seated, then 2/3 turn is to correctly compress the washer.
13lbft torque is near the top of the recommended for aluminum heads with a 14mm plug.

Once you crush once then you must torque, or go by feel.

Running them to tight is hard on plugs and heads. You’d be better off to pull them and clean, then properly torque.

Steel plug vs aluminum head? I think the head is the weaker part here.

I just don't feel right without my torque wrench in this application.