On July 11, 2018, about 1920 eastern daylight time, an experimental, amateur-built Glasair SH2, N352GL, was substantially damaged when it was involved in an accident near Passadumkeag, Maine. The commercial pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot performed a preflight inspection, noted 19 gallons of fuel on board, and reported that there were no anomalies before takeoff. The pilot climbed the airplane to 1,200 ft mean sea level (msl) and noted that the engine parameters were "normal." About 10 miles southwest of the airport, the engine started to run "rough" and lost partial power. The pilot checked the engine gauges, noted no irregularities, and unsuccessfully attempted to restore engine power by turning the fuel boost pump on. Within about 30 seconds of the initial power loss, the engine lost total power and the propeller stopped turning. The pilot performed a forced landing to a bog, during which the airplane came to rest inverted and the empennage separated. Examination revealed that the No. 4 connecting rod exhibited thermal discoloration and impact damage. The No. 4 connecting rod journal was fractured, exhibited thermal discoloration, and rotational scoring. The crankshaft was removed from the engine and was found fractured at the forward section of the No. 4 connecting rod journal. The Nos. 1 and 2 main bearing journals exhibited no anomalies. The No. 3 main bearing journal exhibited rotational scoring and wear. The No. 4 main bearing journal exhibited a small amount of wear on the forward section, but no anomalies were noted. All of the crankshaft oil passages were free of debris. The Nos. 1 and 3 connecting rod journals revealed no anomalies. The No. 2 connecting rod journal exhibited rotational scoring. The No. 4 cylinder journal had fractured perpendicular to the crankshaft direction, located along the radius at the web forward of the journal. About half of the fracture surface exhibited smearing, consistent with post-fracture damage to the forward surface. The lower half of this fracture surface exhibited crack arrest marks, consistent with progressive crack propagation. The crack initiation site was located on the journal surface, denoted in Figure 1. Figure 1. Angled view of the aft fracture surface, facing the crack initiation area. Yellow area points to the crack initiation area. Closer examination of the fracture surface revealed fatigue striations consistent with fatigue crack propagation. These striations were finely spaced and exhibited changing or erratic thicknesses on different areas of the fracture surface, consistent with propagation through high-cycle fatigue. Outside of the fatigue regions, only dimple rupture features were found, consistent with subsequent and final overstress fracture of the crankshaft journal. Examination using a scanning electron microscope found three primary initiation sites, with possible smaller initiation sites collocated in the area. These initiation sites were all located on the fracture surface edge with the journal surface. There were no material features (such as cracks, pores, or voids) located at these initiation sites. However, mechanical defects, such as gouges and streaks, were present at the crack initiation sites. Whether the mechanical damage to the journal surface was entirely present before the crankshaft fracture, or if the damage developed after the final fracture of the part could not be determined. According to the engine maintenance log, on March 25, 2013, at a tachometer time of 324.4 hours, the "engine experienced a propeller strike during a landing incident. Crankshaft flange dials 0.001 or less. According to FAA Advisory Circular AC 39-7D, 9b prop strike inspection AD 2004-10-14 is not mandatory on a non type certificated (experimental) engine. Although recommended, I have elected not to have the inspection performed and accept all future responsibility related to non-compliance of the airworthiness directive."