Complex sentence: It had a combination of 4 2-piston engines; the larger, the expansion piston/cylinder, being 4.267 meters or 14 feet in diameter--perhaps the largest piston diameter of any engine ever built.
Split into simpler sentences: It had a combination of 4,2 piston engines, the larger, the expansion piston/cylinder, being 4.267 meters or 14 feet in diameter. Perhaps the largest piston diameter of any engine ever built.