Accident Overview
The pilot was conducting aerial spraying of sulfur on a carrot field when the engine lost power. The pilot executed a forced landing in an adjacent alfalfa field; the airplane came to rest inverted. The pilot had noted an increase in oil consumption earlier that day.
Witness Observations
A witness reported seeing two puffs of black smoke emanating from the airplane shortly before the forced landing.
Engine Inspection Findings
During the post-accident engine inspection, the number 5 exhaust rocker arm was found broken. Further disassembly of the number 5 cylinder revealed that the exhaust push rod was bent; however, based on its appearance and length, it was determined to be the intake push rod. When the exhaust push rod and the intake push rod were placed side-by-side, the intake push rod was the longer of the two and was the one that was bent.
Maintenance personnel indicated that the only way an intake push rod could be installed in the exhaust side of the cylinder was to loosen the cylinder and pull it away from the case to allow an increased distance between the rocker arm and lifter. When the cylinder was re-torqued with the push rods in a switched configuration, the longer intake push rod would bend within the exhaust housing. After replacement of the push rods and the broken rocker arm, an engine run was conducted with no anomalies noted.
Maintenance History
Review of the engine logbook revealed that a major overhaul had been performed on the engine approximately three months prior to the accident. Records indicated that a mechanic and an inspector conducted an inspection of the cylinders and associated components; the engine was test run with no discrepancies and then inspected by a different mechanic and inspector. All four individuals signed off on the engine as being in airworthy condition and returned to service. A review of the engine logbooks also showed that maintenance had been performed on the airplane since the overhaul, but not in the area of the number 5 cylinder.