This engine was running and was an odd site to see. The engine, on the left, ran and pulled the belt. On the right are two pistons that pumped as the wheel (behind the yellow guard) moved their shafts. Even better, the hose is connected to the pipe with the red handle; if you put your hand on the top, the air being pumped would blow through pipes (next to the pressure gauge) and toot.
(Click the image to view a smaller version.)