On August 13, 2017, about 1700 eastern daylight time, a Piper J3C-65, N98550, operated by Berkshire Aviation Enterprises Inc., was substantially damaged during a forced landing into trees, following a total loss of engine power in cruise flight near Salisbury, Connecticut. The flight instructor and student pilot sustained minor injuries. The local instructional flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and a visual flight rules flight plan was filed for the flight that departed Walter J Koladza Airport (GBR), Great Barrington, Massachusetts, about 1640. The flight instructor reported that he was providing an introductory flight to the student pilot in that particular make and model airplane. About 20 miles south of GBR at 2,800 feet mean sea level, the airplane experienced a total loss of engine power. The flight instructor took control of the airplane from the student pilot and positioned the carburetor heat to on. He also verified that the fuel selector was in the on position and the magneto switch was set to both, but the engine did not regain power. There were no suitable landing areas nearby and the flight instructor elected to perform a slow landing into treetops. The airplane subsequently collided with trees and came to rest nose-down entangled in the trees. The airplane was equipped with a Continental Motors C90-8F, 90-horspower engine. The airplane's most recent annual inspection was performed on July 13, 2017. At that time, the airframe had accumulated 2,093 hours of operation. Review of the engine logbook revealed that maintenance records prior to 1994 were lost and a new engine logbook was created in June 1994, indicating that the engine was overhauled at a total estimated time of 1,300 hours. In October 2013, at 689 hours since major overhaul, the engine was disassembled and inspected after being involved in a previous accident (NTSB ID # ERA11LA379). During that work, the crankshaft was replaced per "Continental Overhaul Manual dated 1-1994." The engine had accrued about 317 hours from the time of the most recent crankshaft replacement, to the most recent annual inspection. Examination of the wreckage by a Federal Aviation Administration inspector revealed substantial damage to the wings and fuselage. When the inspector rotated the crankshaft by hand, he was unable to confirm thumb compression to two cylinders or continuity to the rear accessory section. A teardown examination of the engine was subsequently completed at the manufacturer's facility, under the supervision of an NTSB investigator. The examination revealed that the crankshaft gear screws were fractured, and the crankshaft gear was separated from the crankshaft. Fretting was observed near two of the four crankshaft screw holes and corresponded to two elongated screw holes on the crankshaft gear. The crankshaft gear contained an oil stain witness mark in an area that coincided with a dowel pin hole on the crankshaft; however, the crankshaft and crankshaft gear did not contain a dowel pin as specified in the most current version of the manufacturer illustrated parts catalog (IPC) and overhaul manual (OM). Additionally, the crankshaft gear did not contain a dowel pin hole, which was consistent with a crankshaft gear for a C65 engine and not a C90 engine. The manufacturer's most recent IPC and OM were published in August 2011, which was more than 2 years prior to the most recent crankshaft replacement in 2013. Both publications contained numerous instructions and references to use a crankshaft gear with a dowel pin hole and align the gear to the crankshaft with a dowel pin, which would pilot the crankshaft gear on the crankshaft.