| Engine Basics |
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How does this explosive power get turned into rotating power? The engine has a crankshaft below the pistons. It looks like a straight shaft with bends, called “throws,” in it. A connecting rod connects the bottom of the piston to one of the throws in the crankshaft. Downward pressure from the piston rotates the throw in the crankshaft, and thus rotates the crankshaft itself. Car Words A crankshaft converts the pistons’ up-and-down motion into a circular motion that can be used by the transmission and, eventually, the wheels. Bicycle pedals move up and down in the same way to rotate the rear wheel. Fortunately, car engines don’t have just one cylinder and one crankshaft throw—otherwise the car would lurch down the road with each firing in cylinder. Cars have four, six, or eight cylinders. That means the crankshaft has four, six, or eight throws connected to the bottom of a piston. By simply timing the explosions and placing the crankshaft throws at angles, the crankshaft’s rotation can be controlled so it isn’t fighting itself. The crankshafts rotation turns a round flywheel that turns other parts you’ll soon learn about, including the car’s wheels. As you can imagine, there are lots of fast-moving parts in an engine. Pistons, valves, and the crankshaft to name a few. How do they keep from quickly wearing out? Another job of the engine is to deliver oil to parts as needed. Your job will be to make sure the engine has enough quality oil to do its job. All this combusting makes heat. Lots of heat. So your engine also has a cooling system that removes heat from inside the engine. Therein lies another easy job you’ll do: keep the cooling system working well. The crankshaft’s rotation also turns other things on the engine. Belts connect and drive these parts. Some things need to be timed to rotate together so timing belts are important to an engine. You’ll learn lots more about engines, lubrication, cooling, and belts as you discover how to take care of your car.
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A piston is simply the movable floor in an engine’s combustion chamber. The fuel comes into the chamber through a valve that functions like an automatic door. When the chamber is smallest (the piston has moved up as far as it can go), an electric spark detonates the fuel and causes a controlled explosion. The explosion pushes on all the chambers walls, but only the bottom wall of the chamber, the piston, can move so it is pushed down. (Just so you know: an exhaust valve opens as the piston comes back up and pushes the burned air out of the cylinder.)
