THE PLT ESTIMATED THAT THE DURATION OF FLT WOULD BE ABOUT 5 TO 5-1/2 HRS & THAT HE HAD APRX 7 HRS OF FUEL ON BOARD. HOWEVER, THE ACFT ENCOUNTERED HEAD WINDS DURING THE FLT, & AS IT WAS APPROACHING THE DESTINATION, THE ENG LOST POWER AFTER APRX 6 HRS OF FLT. SUBSEQUENTLY, AN EMERG LANDING WAS MADE ABOUT 1 MI FROM THE ARPT. DURING THE LADNING, THE NOSEWHEEL HIT A CLUMP OF GRASS & SEPARATED FROM THE ACFT. NO PREIMPACT PART FAILURE OR MALFUNCTION WAS FOUND THAT WOULD HAVE RESULTED IN THE ACDNT. A FUEL LINE WAS BROKEN DURING IMPACT WHICH ALLOWED FUEL TO DRAIN; THEREFORE, THE EXACT AMOUNT OF FUEL ON BOARD AT THE TIME OF THE ACDNT COULD NOT BE VERIFIED. THE INVESTIGATOR ESTIMATED THAT 93.5 GAL OF FUEL WOULD HAVE BEEN REQUIRED AT OPTIMUM CONDITIONS. THE ACFT'S FUEL CAPACITY WAS 90 GAL OF WHICH 1 GAL WAS UNUSABLE. THE PLT BELIEVED THERE WAS STILL USABLE FUEL ON BOARD WHEN THE ENG LOST POWER & SAID THAT HE HAD THE FUEL SELECTOR SET FOR THE FULLEST TANK.