On March 18, 1995, at 1110 central standard time, a Piper PA- 28R-201, N47839, was substantially damaged during a forced landing near Devine, Texas. The commercial pilot was not injured. Visual meteorological conditions prevailed for the personal cross country flight. No flight plan was filed for the flight which was flown under Title 14 CFR Part 91. According to the pilot, the aircraft had just come out of an annual inspection and new engine installation. The pilot stated that he completed a detailed preflight and runup with the cowling removed. After taking off, the pilot cycled the landing gear a couple of times while in the airport vicinity, before heading for Devine, Texas, at 1,800 feet. Ten minutes into the flight the engine oil annunciator light came on and the oil pressure gauge indicated that oil pressure was falling off. The pilot elected to execute a forced landing to an open field. The field selected was a freshly plowed sandy field. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that the an unapproved quick oil drain was installed on the engine. The oil drain was found in the open position. Further investigation revealed that the oil drain was inadvertently opened by the nose gear drag link during the nose retraction cycle resulting in the loss of oil.