On November 27, 2022, about 1130 eastern standard time, an experimental amateur-built Rotorway Exec 162-F helicopter, N8006A, was substantially damaged when it was involved in an accident near the Space Coast Regional Airport (TIX), Titusville, Florida. The flight instructor and the pilot trainee were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor, who also owned the helicopter, stated that shortly after takeoff, while about 150 ft above ground level, the engine lost partial power with “severe backfiring.” He declared an emergency, turned back to the airport, and landed on a grassy area. Upon touchdown, with a ground speed of 5-10 mph, the helicopter’s front left skid dug into the grass. The helicopter entered a dynamic rollover and came to rest on its left side, resulting in substantial damage to the tail boom and main rotor blades. Postaccident examination of the engine revealed the No. 4 exhaust valve spring retainer was missing. Review of the engine maintenance manual revealed the valve train system including the spring retainer, was to be inspected every 25 hours. The manual stated, “Note the relative depth of the keeper set in each spring retainer. You may notice a slight variance on different valves, but no keeper set should be sunk deeply into a retainer. The important thing to look for is any change in the relative position of each keeper set. If you determine that a keeper set seems to be sinking deeper into its retainer, DO NOT continue to operate the engine.” A review of the engine logbook revealed that the instructor/owner performed the 25-hour inspection on October 11, 2022, about 8.8 hours before the accident.