hello, you clearly have a fault in the engine or the wrong choice of plug.
I dont think this random diagnosis of your problem would be of any value to you without some idea of what condition your plugs display when they fail.
the engine may require a hotter or cooler plug.
you may have seroius pre-ignition due to erroneous ign timing, carbon fouling inside the combustion chamber, or excessive compression ratio. so the excees temperatures generated, or concussion due to the shock wave simply kills the plug.
the mixture may be way off causing burning - too weak - or fouling - too rich.
do you have a ballasted - 8 or 9 volt - coil in a non ballasted - -13 volt -cicuit giving up to 50% excess high voltage sparks.
a misfire will cause bigger bangs during the following firing stroke - causing detonation damage.
fouling due to engine running too cool and/or too rich prevent efficient sparking leading to carbon tracking.
so many possible causes, but no clues/symptom to narrow the choice.
