On July 4, 2024, at 1600 eastern daylight time, a Bellanca 8GCBC, N749SK was substantially damaged when it was involved in an accident near Frankford, Delaware. The commercial pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 banner towing flight. According to the pilot, the airplane was based at Bunting's Field Airport (4MD1), Berlin, Maryland. Before to the first flight of the day, the pilot added a quart of oil to the engine and completed a preflight inspection with no abnormalities noted. He also added fuel to the airplane and conducted an engine run-up that was normal. The pilot then departed and flew several aerial advertising banner flights throughout the day without incident, adding fuel as necessary. During the accident flight, with the banner in tow, he proceeded to fly from 4MD1 to the Ocean City, Maryland, inlet at 1,000 ft mean sea level (msl), then descended to 300 ft msl and flew north along the Rehoboth Beach coast during the advertising portion of the flight. The flight was uneventful, and all engine indications and airplane performance were normal and “in the green.” However, toward the end of the route, the engine oil temperature, which usually was about 190° F, indicated about 220° to 230° F. The pilot advised the operator of the higher-than-expected oil temperature and was informed by the operator that it was within limits as the outside air temperature was hot that day. As the pilot approached the end of the advertising portion of the flight, he initiated a climb to 1,200 ft msl; however, the airplane would not maintain altitude even though the throttle and mixture controls were full forward. The airplane was slowly descending, while the engine rpm was dropping with simultaneous engine roughness that was increasing in severity. The pilot elected to drop the banner over a vacant field as the airplane descended through 700 ft msl. As the airplane reached 500 ft msl, it exhibited a further reduction of engine power. The pilot intended to perform a forced landing to a field; however, the airplane was unable to reach the field, and the airplane impacted the top of trees. The airplane then descended to the ground inverted, which resulted in substantial damage to the wings and airframe. Examination of the airframe and engine revealed fuel and oil were present. The engine’s crankshaft was rotated via the propeller and crankshaft and valvetrain continuity were confirmed. There was compression on each of the cylinders. Erosion damage was noted on the edge of the No. 3 cylinder intake valve and valve seat insert, which also included a cracked lower spark plug. A review of the maintenance records revealed the that the No. 3 cylinder assembly was replaced with a new cylinder during the annual inspection 45 days before the accident. The airplane was subsequently signed off as airworthy.