The pilot stated that while returning to the airport, the helicopter’s engine rpm dropped to zero with no warning. He initiated an autorotation and aligned the helicopter to touch down in an open field but noticed powerlines as he got closer. The pilot maneuvered away from the field and aimed for a clearing in a residential backyard. The main rotor blades impacted a tree, and the helicopter fell about 15 ft to the ground before it came to rest on its right side. The helicopter sustained substantial damage to the fuselage and main rotor blades. According to maintenance records, the engine was removed and replaced about a month before the accident. Additionally, a condition inspection was completed by the owner four days before the accident during which he changed the spark plugs and adjusted the fuel mixture. A post-accident examination revealed corrosion at the radiator fill tube connection and a loose band clamp. Additionally, the engine exhibited signatures consistent with being operated at a temperature above the normal operating temperatures and evidence of piston seizure due to thermal expansion.