The undetected wear of both pawl retaining rivets of the left magneto impulse coupling and fatigue failure of one pawl retaining rivet, which led to cascading fractures of the second pawl retaining rivet, left gear retainer assembly, and gear teeth of multiple gears in the accessory section of the engine and resulted in a loss of engine power. Contributing to the accident was the lack of current information available to the pilot regarding the status of a nearby airport’s closed runways.