soxinbox wrote:
/snip/

Later I took a close look at the failed plug. It has a crack from about 1/4
inch from the seat to 1/8 inch from the threads for the plug wire retainer.
The crack is not opened up, but is a distinct fine crack about 2 inches
long. Is this a normal failure for a spark plug? What can cause this kind of
crack? Is this indicative of a manufacturing problem?



Is the crack in the outer, metal shell of the plug, or the inner ceramic
lining?

Happy Flying!
Scott Skylane
N92054