This engine is not set up as a 4-stroke internal combustion engine - it is an air motor. The giveaway is in the camshaft gearing - a 4-stroke IC engine would require a 2:1 drive to the camshafts, but the engine pictured has 1:1 drive (gears same size). The "water pump" is the horizontally-opposed 2 cylinder affair mounted to the front of the timing gear cover, and in this example would be for show only. None of this diminishes the incredible, painstaking craftsmanship which went into this creation. What a beautiful machine!