We learned a long time ago to bomb-test even brand-new
plugs. We've had new Champs fail right out of the box. It can't be just
a tiny crack in the resistor; there has to be something else going on
here. When I remove that screw inside the barrel and take out the
spring and resistor, I can't find anything wrong with it. And if I take
that stuff out of a working plug, it doesn't want to work again after
reassembly. I think there's something wrong with the spring-loaded
resistor concept.
The old Auburn plugs had a molded-in resistor that seldom
failed, and AC copied that idea but have had some trouble anyway.
Now here's a debate: The resistor was originally to reduce
radio interference in automotive plugs. Since aircraft plugs are
shielded, that's not necessary. The textbooks say that the resistor is
there to shorten the spark duration and reduce electrode erosion.
Wouldn't it be better to leave the resistor out and accept shorter but
consistent plug life?

Dan