Incident Overview
During a flight, the pilot encountered an engine vibration. Shortly thereafter, oil began appearing on the windscreen. While maneuvering toward suitable terrain, the #2 cylinder detached from the engine. A forced landing was made in a field. Upon landing, the aircraft struck several fence posts, and the landing gear collapsed as it traversed rough and uneven terrain.
Engine History and Examination
Engine records showed that a top overhaul had been performed approximately 172 flight hours before the incident. During that overhaul, the cylinders were removed and replaced. A subsequent metallurgical examination of the engine revealed that several cylinder hold-down nuts had backed off their bolts, or the bolts themselves had separated due to fatigue. These conditions allowed the cylinder to break free of the engine case.
Maintenance Findings
The mechanic who conducted the top overhaul reported using a silicone sealant between the cylinders and their respective engine case halves. According to the investigation, the application of this uncalled-for sealant could result in a reduction or elimination of the preload torque applied to the through-bolts and hold-down studs.