On June 20, 2014, about 1035 central standard time, a Grumman G-164 agricultural airplane, N455Y, sustained substantial damage following a forced landing after a loss of engine power in the vicinity of Anadarko, Oklahoma. The commercial rated pilot, who was the sole occupant, sustained serious injuries. The agricultural flight was being conducted under the provisions of Federal Code of Regulations Part 137. Visual meteorological conditions prevailed throughout the vicinity and a flight plan was not filed. The local flight originated from a private agricultural airstrip near Anadarko, Oklahoma, at 1030. According to the pilot, the airplane had been running well on previous flights. After which, he discovered that oil was leaking from the magneto gear seals of the Pratt & Whitney R-985 radial engine. On October 18th, the pilot said that he called a repair station (Covington Aircraft) to have a mechanic come to replace the magneto seals. On October 19th, a mechanic arrived and replaced the magneto seals. The mechanic also gapped the points prior to reinstalling the magnetos. After the work was completed, the airplane engine was started by the pilot and the magneto check was measured as normal. The pilot stated that he thought that the airplane was fixed on the morning of the accident flight, so he loaded with 200 gallons of pesticide, warmed the engine for 30 minutes, and taxied to the departure runway. During the engine run up, the pilot did a successful magneto check and all engine gauges appeared normal. During takeoff, the airplane came off the ground normal and was climbing out. While departing toward the northeast, the engine began to lose power. As the pilot made a turn back to the airstrip, the engine lost all power. Within about 100 feet of the ground, the pilot elected to land the airplane in a small open field just below the airplane. He thought that the airplane was beginning to stall as he pulled the throttle all the way back and pushed the stick forward. The pilot flared and the next thing that he remembered was sliding backwards with the top of the windscreen scooping up dirt. A summary review of the most recent engine logbook showed an entry dated April 2, 2014. The entry did not show a total engine time and showed 0.0 hours since major overhaul (SMOH), with a test run, inspection, and return to service. The entry on next the next page was dated March 2, 2014, (out of chronological sequence from the prior entry) stating that the engine was overhauled and returned to service. There were no logbook entries found relating to the magneto seals. However, there was separate documentation, dated June 19, 2014, showing a magneto drive seal kit being delivered and installed on the airplane as the pilot reported. Repeated attempts by the NTSB to obtain additional information from the pilot and the pilot's representative were not successful.