How Things Work - 62 free documentaries about engines & machines.
Start with Automata: The Extraordinary "Robots" Designed Hundreds Of Years Ago (59 min, Timeline), then How Does A Carburetor Work? (25 min, Smarter Every Day). All 62 documentaries here are free to watch from their makers' official uploads. To read deeper, the top-rated book on engines & machines is The Way Things Work Now by David Macaulay.