On November 12, 2017, about 1025 mountain standard time, an experimental amateur built Vanderark RV-10 airplane, N917VA, impacted terrain and vegetation during a forced landing following a loss of engine power near Sun Lakes, Arizona. The private pilot was not injured; the airplane was substantially damaged. The airplane was registered to and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight which originated from the Chandler Municipal Airport (CHD), Chandler, Arizona, about 1015.The pilot reported that while about 15 miles south of CHD and climbing through 4,000 ft mean sea level (msl), he noticed the smell of antifreeze and realized the engine was overheating. He reduced power to idle and executed a 180° turn toward CHD. As the airplane descended through about 1,500 ft, he added power but the engine did not respond. He attempted to land at a nearby closed airport, however, realized he was unable to reach it, and subsequently initiated a forced landing to an area of open desert. During the landing roll, the airplane struck several scrub bushes and the nose wheel and left main landing gear collapsed. Examination of the airplane by the pilot revealed that the left wing and fuselage were structurally damaged. The airplane was powered by an LS1 series, eight-cylinder, liquid cooled automobile engine, manufactured by General Motors. It was equipped with two alternators and a water pump to circulate engine coolant. The alternators and water pump were connected by a common "serpentine" drive belt and driven by a pulley on the crankshaft. The pilot reported that at the time of the accident, the airframe and engine had accumulated 51 hours total operational time. Postaccident examination revealed that one of the two alternators was partially displaced, and that its upper and lower attach bolts were fractured. Examination further revealed that the alternator belt had detached. Examination of the fractured bolts was conducted by a specialist from the NTSB Materials Laboratory. The lower attach bolt exhibited a fracture in the threaded portion of the bolt shank. The fracture surface of the lower attach bolt was smeared and damaged by apparent re-contact. The fracture surface was flat and perpendicular to the axis of the bolt shank with an area exhibiting a shear lip on one side. Ratchet marks were observed on the side opposing the shear lip, consistent with a fatigue fracture. The upper attach bolt also exhibited a fracture in the threaded portion of the bolt shank. The fracture surface exhibited ratchet marks on the periphery and crack arrest fronts extending towards the opposing side consistent with a fatigue fracture.