The Mack four-cylinder engine has two separately cast cylinder pair blocks. The cooling fan, which is BEHIND the engine, turns but is not powered. Visible in this photo are the cooling water intake, faux spark plugs and part of the exhaust system. The cross-wise rod in front of the engine represents the accessory drive that runs the water pump and magneto ignition. In the real engine this is driven by gears from the right front part of the engine. Many early trucks didn't have a low voltage electrical system; optional headlights were powered by acetylene gas.