"Tim R" wrote in message
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On Tuesday, May 10, 2016 at 3:24:00 PM UTC-4, Ian Field wrote:


The alumina ceramic on a spark plug is also lossy enough to get red hot.

I believe you, but............how do you know? It's darned hard to get
the ceramic off the steel part before I put it in the microwave.

I was cleaning the plugs - they wouldn't have been much use if I'd removed
the metal bit.

If you leave a plug overnight in an industrial strength ultrasonic cleaner,
it loosens the compacted powder seal - put it in an engine and the seal will
blow out within a mile.

If I want the metal shell to make a 2-stroke TDC measure, I just grind off
the rolled down lip and dig the seal out with a small screwdriver.