On October 2, 2004, at 0900 central daylight time, a Stinson 108, N40129, registered to and operated by a private owner, as a 14 CFR Part 91 personal flight collided with trees during a forced landing to unsuitable terrain following a loss of engine power near Ashland, Alabama. Visual meteorological conditions prevailed and no flight plan was filed. The airplane received substantial damage. The airline transport rated pilot, private pilot passenger, and one rear seat passenger reported minor injuries. The remaining rear seat passenger reported no injuries. The flight originated from Birmingham, Alabama on October 2, 2004, at 0835. The pilot stated they were in cruise flight at 2,500 feet MSL with a private pilot flying the airplane. The engine began to run rough and shudder. The pilot stated, "I have the controls" and the private pilot responded, "you have the controls." The pilot looked for a forced landing area and observed a country road and a field. He completed the emergency checklist and entered a downwind to land on the highway. He turned base and observed power poles, but he could not see any power lines running between the poles and decided to land in the field. He made a left 35-degree turn towards a field and propeller struck a tree, yawed to the left colliding with the ground separating the landing gear and bending the engine firewall. Examination of the engine assembly revealed the exhaust valve in the No.4 cylinder had failed. The No. 4 cylinder and exhaust valve were forwarded to the NTSB Materials Laboratory for further analysis. Examination of the exhaust valve revealed fatigue cracks had propagated from opposite sides of the stem adjacent to the beginning of the radius between the stem and the valve head. The No. 4 cylinder and exhaust valve was returned to the registered owner on January 24, 2005.