19990711008839A

Acft crashed under unknown circumstances and sustained substantial damage. (.4)the pilot stated that the airplane began to vibrate slightly while in cruise flight, and he decided to return to the airport. The engine then began to shake violently, and the pilot performed a forced landing. The airplane landed short, nosed over, and came to rest inverted. Examination of the wreckage revealed that the left rear cylinder on the engine had separated from it's mounting flange. The engine had accumulated about 13 hours since overhaul, when all four cylinders were replaced on the engine with chromed cylinders purchased from an outside source, then overhauled by the engine overhaul facility. During the metallurgical examination of the failed cylinder, a fatigue origin was found near the bottom of the fin radius, between the tenth and eleventh fins from the inboard end of the cylinder barrel. Severe corrosion attack was also observed on the fin immediately adjacent to the fatigue origin location. Corrosion damage was also noted in the radius, including a corrosion pit from which the crack arrest features appeared to emanate. The corrosion pit was filled with a non-conductive substance.