How much torque to install new plugs?

[stanrob]

I'm putting new plugs into my 85 4WD at 303,000mi. Has lost some hill-climb power, diesels at shutoff.
They come pregapped correctly, so far as I can tell.
The question is how much more to tighten them once finger tight.
Autolite says 1/2 turn.
Autolite also specifies two different torque ranges depending on steel or aluminum head. Ours are aluminum, right?
In any case, their advice seems inconsistent.

[splatterdog]

I usually go over spec with 18-20 ft lbs. 14-16 if the threads seem iffy. Anything less never seems to really crush the gasket.

[larry mcgrath]

Make sure you use some anti seize on the threads of the spark plug (alumnium against steel) or you could have trouble with a seized plug later Larry

[splatterdog]

Make sure you use some anti seize on the threads of the spark plug (alumnium against steel) or you could have trouble with a seized plug later Larry

If you do, use sparingly. No car makers use or recommend it. Any quality plug should be plated to reduce corrosion. Black oxide plugs-NO!!!!

I only use it on buggered up iron heads that are getting their last plug. Or Mopars which still use plain champion plugs that tend to rust in. Their 5.7 engines have dual plugs with super long threads that need to be wrenched the whole way out! I've pulled T4 engines in less time...

Also, reduce torque with antisleaze. It does affect the clamping force.

[drege]

Yea I've never used antiseize on plugs, never had a stuck plug in 50+ cars I pulled plugs from - even old flat heads from rusted old equipment.

[Petros]

yes use it sparingly, but it is important to use it. the aluminum is easy to cross thread and get worn out early from threading steel plugs into it eventually. It not only makes it easier to remove later but protects the threads in the head from damage. Dissimilar metals, particularly where high voltage power is run across it (every time the plugs fire), are prone to electrolysis and corrosion.

I once had to use a big breaker bar to remove plugs from an aluminum head that had been in the car for over 100k miles. they were corroded into place, I was worried I was going to break one off. I soaked in ATF and worked it back and forth lots of times, still took lots of strength to get them to move at all. the corrosion buggered up the threads in the head, but fortunately they were good enough so the new plugs will seat and hold securely.

I ALWAYS use thread lubricant on the spark plugs, and anywhere else where there are dissimilar metals in contact with any fasteners. And I have never had fasteners ever frozen in place when I do.

[keith]

I used to recommend torquing spark plugs, but not anymore. As the head ages and many sets of plugs have been replaced, differences develop in the threads so they don't torque equally. Equal torque does not translate to equal clamping pressure. Torque angle is much more accurate. For plugs with a gasket, the best torque angle is 5/8ths turn after seating, for plugs without a gasket, 1/8th turn is the correct amount.

As for using anti-seize, it depends on the plug. Some plugs come plated and may or may not be compatible with anti-seize. Black oxide coated plugs must have some anti-seize compound used on them. Champion used to use a plating that was not compatible with anti-seize, but now I believe that their current plating, along with NGK is compatible. Use of anti-seize is optional with these. Not sure about Denso.

Clean the threads in the head with an old tooth brush or something similar. Screw down the plugs using just the spark plug socket with an extension on it. You can tell when it bottoms out. Then add the required torque angle.

[Petros]

I would never use Champion spark plugs ever, had too many problems with them in many different cars, and chain saws and lawn mowers too. they are junk.

NGK I have had excellent experiance, and only use those if they are available for everything we have that uses spark plugs.

[marlinh]

If you find spark plug threads somewhat damaged, you can run a thread chaser down the spark plug hole to clean it up. If you put grease in the grooves of the chaser it will usually catch the debris that comes off the threads. They are an inexpensive tool and handy to have.

Also, one thing I do when I rebuild a head is chase the spark plug holes. Guaranteed no surprises when you are putting everything together.

[stanrob]

Once again, it's time for me to thank this team for all of your sympathetic advice.
This time I can see that there's a range of opinions on the subject. So I still had to make choices!
After all my fears, and the car's 303,500 miles, this job was a cinch. Actually, that engine is in great shape.
The old, long-used plugs came right out.
Holes and threads were clean. Huge bready deposits on each plug's far end!
I did use antiseize (which I got for the very first time in my life, costing $1.58+tax).
I did use my neighbor's classic torque wrench, torquing to 16 ft-lb, despite SM spec 13 and you guys' 16-18.
I'm glad I did that instead of 5/8 turn; #4 required a couple of extra turns after what I had thought was hand-tight.
(The plugs were Autolite AP64 (platinum). Autolite's online info said 16-18 ft-lb or 1/2 turn.)
Next week I'll be testing it on the infamous Route 2 hill out of Cambridge MA.
In closing, THANK YOU for your enthusiastic support.
Now, I must turn my attention to a troubled differential.