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Has anyone ever heard of spark plugs consistently going bad after about one hour of run time? I have experienced this about three or four times in a row where I install a new spark plug (gaped to .035) on my newly rebuild k241a, run the engine, turn it off, come back to start it only to find that the plug will no longer spark. I thought that I may have been cracking the insulator while I am putting them in, although I am very careful doing it, torquing them in stages to 20 foot pounds. I have inspected them all and no cracks are visible on the insulator portion. One thing I do notice in a big way is the shock from the plug when I crank the engine and the plug not grounded. When I do that, a spark will come off the metal shell of the plug to the engine block, instead of between the electrodes.