Precautionary Landing and Repair
The pilot, who also served as a mechanic, arrived at Seminole Lake Gliderport to repair the engine following an uneventful precautionary landing the previous day due to a bent exhaust pushrod on the No. 2 cylinder. He replaced the damaged pushrod, pushrod housing, pushrod seals, and lock tab. He visually inspected the valve springs, which did not appear damaged, but did not inspect the valve or remove the cylinder. After repairs, the engine was started and a full static run-up was performed with no discrepancies noted.
Flight and Accident
The flight departed for Kissimmee Gateway Airport. Shortly after takeoff, the engine began running rough, though it still produced power. The pilot elected to return to Seminole Lake Gliderport. Recognizing that he would overshoot the runway with reduced engine power, he performed a 360-degree turn back onto final approach. During the turn, the aircraft impacted trees and came to rest in a swamp south of the south edge of runway 18.
A pilot-rated witness observed the airplane on final approach. As it descended to treetop level or building height, the airplane abruptly pitched up and down and yawed abruptly. The witness noted that some of the airplane's motions did not coincide with the observed wind conditions.
Postaccident Examination
An FAA inspector examined the engine and found that the replaced pushrod was damaged on both ends, with no obvious indication of a stuck valve. Additionally, the rotator type exhaust valve stem cap was missing from under the exhaust rocker arm of the No. 2 cylinder. The exhaust valve and guide were within new limits per the Lycoming overhaul manual. There was no evidence of carbon inside the guide, but swirl marks from reaming of the guide were present.
Review of Lycoming Service Bulletin (SB) No. 388C revealed inspection procedures to be carried out at 400 hours or earlier when valve sticking is suspected. The SB indicates that failure to comply could result in sticking valves or broken exhaust valves, which could lead to engine failure. A section of the SB outlines an inspection procedure using a GO/NO-GO gage and recommends moving the exhaust valve completely out of the guide to avoid interference when checking for wear or carbon buildup. The mechanic did not report using the GO/NO-GO gage or a locally manufactured tool.