On June 4, 2023, at 1130 Pacific daylight time, a Piper J-3C-65, N77583, was substantially damaged when it was involved in an accident near Belfair, Washington. The flight instructor and the student pilot were seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor stated that he and the student pilot had been practicing maneuvers before they proceeded toward the Bremerton National Airport (PWT), Bremerton, Washington. The student pilot performed the before-landing checklist, which included checking fuel and turning on carburetor heat, as they were about 2 miles from runway 02. Shortly after, they heard a loud noise followed by a total loss of engine power. The flight instructor took control of the airplane and initiated a forced landing to an open area. During the landing roll, the airplane impacted rough and rising terrain. The left wing partially separated, and landing gear collapsed, which resulted in substantial damage to the fuselage. A postaccident examination of the airframe and engine revealed that, when the propeller was rotated, neither magneto coupling could be heard firing. The right magneto was removed, and remnants of the crankshaft accessory drive gear were observed in the accessory case. No additional, non-impact related anomalies were noted with the engine or airframe. The engine was disassembled, and the crankshaft and the gear remnants were removed and sent to the National Transportation Safety Board Materials Laboratory for further examination. The fracture faces of the gear contained mechanical damage. Two of the fracture faces contained fatigue striations typical of fatigue cracking that emanated from the root of the gear. The fatigue crack in these two gear fragments extended through the entire width of the gear. The terminus of each fatigue crack was not defined because of the severe mechanical damage on the fracture faces. The engine had accumulated about 278 hours since last overhaul and about 20 hours since the last annual inspection. The total number of hours on the engine could not be determined.