According to the pilot, she performed a normal preflight of the airplane. The takeoff was normal, and as the airplane reached 5,500 feet msl, she heard a subtle 'pop.' She checked the oil pressure and temperature; both were normal. The fuel pressure was in the green and she leaned the mixture slightly. As the pilot reached for the mixture control she heard another 'pop.' In the next few seconds, the propeller blades stopped turning and "froze in the horizontal position." She attempted to restart the engine; however, it seemed to her that the starter was functioning, but the propeller would not rotate. She realized that she was not going to make her destination airport, but knew that she had enough altitude, and began to look for a suitable landing site. The first two places she chose had too much traffic, and as she descended she noted power lines. The pilot spotted a road with no cars or power lines and decided to make the emergency landing. As she made the approach, she noted that the road was "very narrow," with flat terrain and a lot of natural desert vegetation. The airplane landed normally; however, on the landing rollout the left wing struck a Palo Verde tree and the airplane ground looped. The pilot stated that the airplane was a homebuilt replica with a 1929 Wright Whirlwind R540A engine. She listed the time on the engine as 27 hours since overhaul; the airplane had 23 hours total time. She also reported that the shoulder restraint system installed saved her life. A National Transportation Safety Board investigator and an Federal Aviation Administration (FAA) inspector examined the engine, and noted a large hole on the right side of the engine case. On December 14 and 27, 2007, the FAA inspector assigned to this accident inspected the engine and found the following conditions. The master rod experienced excessive heat in the area of number 2 and 3 knucklepins. Number 3 articulating rod became separated from the master rod and also broke free of the piston above the wrist pin. Damage to the other cylinders and connecting rods appear to have been caused when the number 3 articulating rod began running around inside the engine. The engine seized when the number 3 articulating rod bent the number 4 articulating rod and then moved into the bottom of the number 5 cylinder, forcing itself between the bottom of the piston and the master rod.