Amateur-built ZODIAC 650B N452VC accident near Eufaula, Oklahoma

Probable cause

The loss of engine power due to a push rod that was incorrectly installed by the airplane owner.

NTSB analysis

According to the pilots, who were both owners and builders of the airplane, while maneuvering during a local flight, the engine began to run rough. The engine power continued to decrease until they could not maintain altitude. Unable to reach 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 engine revealed the No. 5 cylinder exhaust valve rocker arm attach stud/bolt had failed. 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. The incorrect installation did not allow lubrication to reach the rocker arm, causing it to fail.

Text from the NTSB. Open the NTSB docket for CEN22LA315 for the full record.