Complex sentence: Throughout the years of production, the engine changed very little; the fuel tank was moved from halfway up the engine to the top, and the shaft drive magneto was replaced by a chain-driven unit in the early 1930s.
Split into simpler sentences: Throughout the years of production, the engine changed very little. The fuel tank was moved from halfway up the engine to the top, and the shaft-drive magneto was replaced by a chain-driven unit in the early 1930s.