NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The private pilot reported that the personal local flight was uneventful until the engine made an odd noise, which was followed by a partial loss of engine power. The pilot attempted to troubleshoot the problem, but the engine power was not fully restored, and the airplane was unable to maintain altitude, so the pilot made a forced landing to a road. The airplane struck power lines and vehicles before coming to rest on a sidewalk.
Postaccident examination of the engine revealed that the No. 3 cylinder’s intake valve had separated. The valve stem was found in the oil pan, and the remainder of the valve was found in its intake manifold. Metallurgical examination of the No. 3 cylinder assembly, including the fractured intake valve, revealed that the valve was fractured in the stem in two places and through the head in one place. The interior of the cylinder exhibited damage consistent with impacts from the fractured valve. The connecting rod was intact, but the bearings were worn through both the babbit and copper layers. Examination of the fracture surfaces revealed fatigue cracks initiating from the fillet radius between the valve stem tip and the key area of the stem shaft. The other fractures were consistent with overstress.Further examination of the engine case revealed that all eight hydraulic valve tappet plungers were installed 180° opposite of the proper installation contained in the manufacturer’s overhaul manual. The reversed installation of the plunger would have adversely affected the operation of the No. 3 cylinder’s intake valve and placed an abnormal load on the valve’s tip. A review of the engine’s maintenance logbook revealed that the engine had been repaired about 35.7 hours before the accident. At that time, all four cylinders were removed and replaced, including the hydraulic valve tappet plunger assemblies. Given that the cylinders had been recently removed and reinstalled on the engine, including the hydraulic valve tappet plungers, it is likely that the engine experienced a partial loss of engine power due to maintenance personnel’s improper installation of the No. 3 cylinder’s hydraulic valve tappet plunger.