ZENITH ZODIAC 650B

Full Narrative

On July 12, 2022, about 1000 central daylight time, a Zenith 650B airplane, N452VC, sustained substantial damage when it was involved in an accident near Eufaula, Oklahoma. The pilot and pilot-rated passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.
According to the pilots, who were both owners and builders of the airplane, while maneuvering during a local flight to adjust the airplane’s autopilot, the engine began to run rough. The engine power continued to decrease until they could not maintain altitude. Unable to make a nearby airport, the pilot flying elected to perform an off-airport emergency landing. During the landing, the airplane impacted uneven terrain, which resulted in substantial damage to the right wing.
Postaccident examination of the Corvair conversion engine revealed the No. 5 cylinder exhaust valve rocker arm attach stud/bolt had failed (see Figure).


No. 5 cylinder valve components (Photograph provided by the Federal Aviation Administration)

About 5 flight hours before the accident, the owners had replaced the No. 5 cylinder exhaust valve, which included the removal and reinstallation of the rocker arm hardware. The push rod contained an oil passage hole on one end that allowed for lubrication of the rocker arm, and the other end did not contain an oil passage. According to the owner, during the installation he incorrectly installed the push rod in a backward position.