SloopJohnB@mac.com

Shouldn't (never say never) use helicoils on a spark plug hole...use a threadsert. Timesert is one trademark name.
Reason is that a helicoil does not have a correct gasket or seat configuration. Putting a tapered seat spark plug in a hole repaired with a helicoil is not so good. You might get away with it on a regular flat gasket spark plug, but still:


http://www.timesert.com/html/sparkplug.html

Huskerbob

Sorry I used helicoil sort of generically. You are correct that a threadsert is the proper way to do a spark plug hole.

Dr_Evil

I do not believe for a minute that that plug was sheared due to proper torque and anti-seize. It was over torqued. Plain and simple. Lubricated fastener torque values are only 10% less than dry torque values. If you torqued it to 15 ft-lbs wet you've achieved the equivalent of 16.6 ft-lbs dry. Certainly, that will not shear a spark plug thread housing.

I agree that anti-seize should not be used on any fastener unless it's a very special and uncommon situation, at which point you will probably already know dry torquing is not adequate.

Galvanic corrosion is not an issue between steel, zinc, and aluminum. Look up a galvanic corrosion index.

Dr_Evil

Nope. The spark plug manufacturer will tell you in installation instructions the plug came in if it is necessary. All decent plugs have a zinc plating on the threads for corrosion protection and for anti-galling tendencies when driven into steel.

Secondly, you should not use a torque value to set them. The installation instructions clearly indicate to turn it a certain amount past the seat just to compress the sealing washer. Remember you are not clamping anything with spark plugs. You are just making a compression seal.

Dr_Evil

Anti-seize manufacturers are in the business of selling you anti-seize. Do not use it.

Dr_Evil

Use it dry and turn it the amount necessary to compress the seal washer.

Dr_Evil

You will NOT have galvanic corrosion between zinc plated steel and steel or aluminum

aTOMic

Where did you find this nugget of misinformation?

Dr_Evil

...you can go here,

http://en.wikipedia.org/wiki/Bolted_...ing_the_torque

and down the page under "setting the torque" it discusses how lubricating threads increases the preload beyond the typical 75% target elastic elongation of a bolt, which torque values are calculated to. I think the 15 to 25 percent is a little high but it makes a reasonable point.

SloopJohnB@mac.com

Moreover, BMW recommends antiseize on NGK plugs. I'll take BMW's word for it.