Autozen, you are spot-on with your comment on tolerances. I was just suggesting that I was so close to the release point that absolutely any pressure would cause the valve to open, and that the pressure could have come from any lengthening of the rod, in this case via microexpansion from the manifold heat. Probably could not repeat this condition in a million tries. Backing it off one turn, in any case, solved the problem, which is what I was trying to accomplish!

As the Mad Hatter said: "If you don't know where you're going, any road will get you there."

I really appreciate your advice and your posts, my sincere thanks.

BTW, you are also correct re: carbon steel and it's contribution to horological accuracy. For a facinating look at this and other issues regarding the pursuit of zero-variation in timekeeping, a great book is Longitude, please see:

The Story of Longitude by Louise Borden,Erik Blegvad.

And thanks again.

g

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64 230sl, my daily driver
94 E500, sold
98 E320, family and dog hauler
04 C240, safe machine for teen drivers, but a poc
08 audi a4, yes we have gone to the dark side