The recent issue of Moss Motoring- an excellent publication, by the way-contains a tech tip regarding spark plug replacement that poses a potential hazard to many car owners, especially those with aluminum cylinder heads.

I finds no fault with the basic recommendation that spark plug holes be chased with a tap & cleaned before a new plug is installed. This is sound advice for all, regardless of the type of cylinder head.

The statement recommending the use of an anti seize compound is what concerns me. While this may be a good idea for many engines, there are several sets of circumstances where that recommendation may cause just the result it is aimed at preventing. I speak specifically about aluminum heads, such as those found on Morgan Plus 8's. I have no opinion regarding cast iron heads, a subject on which I have
little experience.

First, there are two general types of anti-seize commonly available to the hobbyist, silver, the most common, a low temp product best used for suspension parts, & a copper colored product, usually labeled "High Temperature". The silver, low temp product, will bond to spark plugs in some cases, making there removal from an aluminum head almost impossible without damaging the threads. I learned this the hard way. Should someone else experience this situation, the only way I have found to remove plugs without damage is to unscrew until strong resistance is felt, reverse, spray a good lubricant such as silicon, back out some more, reverse, spray, etc. It may take 10 minutes or more, but better than helicoils. Remember, you should never remove spark plugs from an aluminum cylinder head until it is cool. If you feel anti seize is necessary for your requirements, use the high temp only, & use it very sparingly.

The second, more general situation concerns a particular brand of spark plugs, Champion. These plugs have a factory applied anti seize compound, I am guessing that it is a dry film lubricant. On the old Cooper Automotive web page, there was a tech tip in regard to this, which pointedly suggested that you do not use any other anti seize product on Champion Spark Plugs. In this competitive world, it is safe to assume other spark plug manufacturers may also provide an anti seize coating.

To summarize, do not apply any anti seize to a spark plug without first contacting the manufacturer to check for prohibitions, & never use low temp anti seize on any spark plug, or any other threads subject to high temperatures such as exhaust manifold bolts. It will do more harm than good.