I was surfing the net, looking for a spare set of spark plug tubes and I ran across an article about slant six spark plug selection. It was interesting in that, according to the article, the metal plug gasket (crush washer) is not to be used on the 63-74 heads. I had never given it much thought, and have always used them without any issues (I am aware of). I am particularly interested in how this affects HP applications and extended tip plug use (something I prefer).
What are the thoughts from the forum on using the plug gaskets?

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-MattMan
LEANED & MEAN

The problems I see are:

- The added thickness changes the heat range of the plug. (not as big of deal with extended tip plugs)

- Exposes the last threads in the spark plug hole. Those exposed threads quickly fill with carbon deposits, making it hard to seat the next plug and correctly compress the tube's O-ring. ( if the next plug is installed with-out the metal gasket)

- The metal gasket tends to smash a groove into the tube's 'floor', slightly closing down the thru hole and distorting the sealing surface.

I do not know if added another "joint" between the parts, impacts their sealing ability... but is it another potential leak point.
DD

True and correct. See here.
The '63-up heads have a redesigned counterbore at the top of the spark plug hole; the spark plug tube itself seals the plug, and if you use the washer it interferes with heat transfer from the plug to the head. The '60-'62 heads don't have the special counterbore and need to use the plug gaskets. This is factory info; following it has always produced best results for me. The idea is to prevent the plug from running too hot; following factory procedure and going without the ring washer means you can dial in just a tetch more timing 'cause your engine is just a tetch less prone to pinging, well, you're that much ahead.

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一期一会
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