While the aircraft was cruising at 2000 feet above mean sea level the engine commenced to run roughly. Trouble checks failed to determine the source of rough running and the pilot elected to land at an enroute aerodrome. However before reaching this strip, the engine lost power completely and the pilot was committed to a forced landing. Because of crowds at an adjacent beach, the pilot attempted to land on a road. Touchdown was further along the road than expected because of a strong tailwind component, and the aircraft collided with a kerb before coming to rest. Investigation revealed that nuts on the various bolts and studs securing the number 3 cylinder to the crankcase had evidently not been correctly tightened. Five of the eight mounting studs/bolts had failed from fatigue during normal operations, finally allowing the cylinder to become loose. The engine had completed 83 hours time in service since an overhaul. There was no logbook record to show whether the particular cylinder had been removed or replaced since that overhaul.