THE PLT STATED THAT SHORTLY AFTER TAKEOFF, HE HEARD A 'LOUD BANG' WHICH WAS FOLLOWED BY A RATTLING SOUND & A LOSS OF ENG POWER. HE HAD TAKEN OFF OVER WATER & ELECTED TO MAKE A 180 DEG TURN TO LAND DOWNWIND ON THE ARPT. THE ACFT TOUCHED DOWN AT ABOUT THE MIDPOINT OF RWY 32R. UNABLE TO STOP, THE PLT APPLIED WHAT POWER WAS AVAILABLE & BECAME AIRBORNE AGAIN, CLEARING CARS ON A HIGHWAY WHICH CROSSED THE DEPARTURE END OF RWY 32. INSUFFICIENT POWER WAS AVAILABLE TO REMAIN AIRBORNE. THE ACFT TOUCHED DOWN IN A RECENTLY PLOWED FIELD WHERE THE RIGHT MAIN GEAR WAS TORN OFF & THE ACFT NOSED OVER. AN EXAM REVEALED THAT THE #6 ROCKER PIN BOSSES WERE BROKEN. A DEEP RIDGE HAD BEEN WORN IN THE INTERIOR FACE OF A BOSS BY A PREVIOUS THRUST WAS HER, & AN IMPROPER OVERSIZED WASHER HAD BEEN INSTALLED WHICH SPANNED THE WEAR AREA. ALSO, A LARGE QUANTITY OF WATER WITH RUST FLAKES WAS FOUND IN THE CARBURETOR BOWL, FUEL STRAINER & RIGHT FUEL LINE.