Hey Dave,

All of us govmunt-licensed airplane mechanics know, that if you drop a
sparkplug (no matter how expensive it is!),
you'd better throw it away; not check the gap and install it!

The porcelain will crack (inside where you can't see), and the spark will
jump to the outer shell thru the crack (instead of at the spark gap),
causing a high-speed miss.  It's because a spark gap is under high pressure
(inside the cylinder), while the crack is at ambient pressure,
so the spark takes the path of least resistance, usually right when you need
it the most (like on take-off or climb-out!)

I have a Champion sparkplug bench-tester that glass-bleads and blows air to
clean, and then tests sparkplugs under pressure.
It has a mirror so you can observe the spark in the pressurized chamber,
before re-use.  If you don't have one of these, don't re-use it!

Bottom line; NEVER re-use a dropped sparkplug.

Mike B.

"Only the quiz/puzzle -- it was either the Car Talk boys, or one of
the automotive-puzzle stories that ran in -- Popular Mechanics, I
think -- when I was a kid.  That's where I learned that if you drop a
spark plug, better check the gap before you stick it in.
Yours,
d"