ENG FAILURE. EMER LNDG ON HWY.

Narrative

WHILE ENRTE TO W13 FROM M52 AT 5500 FT MSL A LOUD EXPLOSION OCCURRED WITHOUT WARNING. VIBRATION OF THE ENG WAS SEVERE. I REDUCED PWR TO IDLE AND THE VIBRATION QUIT. ANY INCREASE IN PWR INCREASED VIBRATION. I KEPT THE THROTTLE TO IDLE AND DECLARED MAYDAY TO ZID WITH WHOM I WAS IN CONTACT THROUGH FLT FOLLOWING. I DETERMINED THE NEAREST ARPT TO BE 10 MI INTO THE WIND AND IMMEDIATELY KNEW THAT IT WAS NOT AN OPTION. I HAD JUST PASSED OVER A 4-LANE HWY SO I TOLD CTR THAT I WAS GOING TO LAND THERE. I THEN FLEW ALONG THE HWY UNTIL I FOUND A SUITABLE AREA. I WAS ABLE TO NAV THROUGH THE ELECTRICAL LINES AND MISS TFC. THERE WERE NO INJURIES AND NO DAMAGE TO THE ACFT OR ANY OTHER STRUCTURES. I THEN RADIOED TO ANOTHER ACFT THAT I WAS SAFE AND HE RELAYED THE INFO TO ZID. THE ACFT WAS TAKEN TO A SALVAGE YARD ADJACENT TO THE HWY WHERE IT WAS REPAIRED BY AN A&E MECH. THE FOLLOWING DAY THE POLICE BLOCKED THE ROAD AND A CFII FLEW THE PLANE OFF THE ROAD AND TO HAZARD; KY; ARPT. THE ENG WAS FOUND TO HAVE PHYSICALLY BLOWN A SPARK PLUG OUT OF THE ENG. THE COPPER WASHER HAD PREVIOUSLY DEFORMED FROM OVER-TORQUING.