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Engine Components

The following is a list of major components found in most reciprocating internal combustion engines (see Fig. 1-15).

  • Block: Body of engine containing the cylinders, made of cast iron or aluminum. In many older engines, the valves and valve ports were contained in the block. The block of water-cooled engines includes a water jacket cast around the cylinders. On air-cooled engines, the exterior surface of the block has cooling fins.
  • Camshaft: Rotating shaft used to push open valves at the proper time in the engine cycle, either directly or through mechanical or hydraulic linkage (push rods,rocker arms, tappets). Most modern automobile engines have one or more camshafts mounted in the engine head (overhead cam). Most older engines had camshafts in the crankcase. Camshafts are generally made of forged steel or cast iron and are driven off the crankshaft by means of a belt or chain (tim- ing chain). To reduce weight, some cams are made from a hollow shaft with the cam lobes press-fit on. In four-stroke cycle engines, the camshaft rotates at half engine speed.
  • Carburetor: Venturi flow device which meters the proper amount of fuel into the air flow by means of a pressure differential. For many decades it was the basic fuel metering system on all automobile (and other) engines. It is still used on low- cost small engines like lawn mowers, but isuncommon on new automobiles.
  • Catalytic converter: Chamber mounted in exhaust flow containing catalytic mater- ial that promotes reduction of emissions by chemical reaction.
  • Combustion chamber: The end of the cylinder between the head and the piston face where combustion occurs. The size of the combustion chamber continuously changes from a minimum volume when the piston is at TDC to a maximum when the piston is at BDC. The term “cylinder” issometimes synonymous with “combustion chamber” (e.g., “the engine was firing on all cylinders”). Some engines have open combustion chambers which consist of one chamber for each cylinder. Other engines have divided chambers which consist of dual chambers on each cylinder connected by an orifice passage.
  • Connecting rod: Rod connecting the piston with the rotating crankshaft, usually made of steel or alloy forging in most engines but may be aluminum in some small engines.
  • Connecting rod bearing: Bearing where connecting rod fastens to crankshaft.
  • Cooling fins: Metal fins on the outside surfaces of cylinders and head of an air- cooled engine. These extended surfaces cool the cylinders by conduction and convection.
  • Crankcase: Part of the engine block surrounding the rotating crankshaft. In many engines, the oil pan makes up part of the crankcase housing.
  • Crankshaft: Rotating shaft through which engine work output is supplied to exter- nal systems. The crankshaft is connected to the engine block with the main bearings. It is rotated by the reciprocating pistons through connecting rods connected to the crankshaft, offset from the axis of rotation. This offset is sometimes called crank throw or crank radius. Most crankshafts are made of forged steel, while some are made of cast iron.
  • Cylinders: The circular cylinders in the engine block in which the pistons recipro- cate back and forth. The walls of the cylinder have highly polished hard surfaces. Cylinders may be machined directly in the engine block, or a hard metal (drawn steel) sleeve may be pressed into the softer metal block. Sleeves may be dry sleeves, which do not contact the liquid in the water jacket, or wet sleeves, which form part of the water jacket. In a few engines, the cylinder walls are given a knurled surface to help hold a lubricant film on the walls. In some very rare cases, the cross section of the cylinder is not round.
  • Exhaust manifold: Piping system which carries exhaust gases away from the engine cylinders, usually made of cast iron.
  • Exhaust: system Flow system for removing exhaust gases from the cylinders, treat- ing them, and exhausting them to the surroundings. It consists of an exhaust manifold which carries the exhaust gases away from the engine, a thermal or catalytic converter to reduce emissions, a muffler to reduce engine noise, and a tailpipe to carry the exhaust gases away from the passenger compartment.
  • Fan: Most engines have an engine-driven fan to increase air flow through the radi- ator and through the engine compartment, which increases waste heat removal from the engine. Fans can be driven mechanically or electrically, and can run continuously or be used only when needed.
  • Flywheel: Rotating mass with a large moment of inertia connected to the crank- shaft of the engine. The purpose of the flywheel is to store energy and furnish a large angular momentum that keeps the engine rotating between power strokes and smooths out engine operation. On some aircraft engines the pro- peller serves as the flywheel, as does the rotating blade on many lawn mowers.
  • Fuel injector: A pressurized nozzle that sprays fuel into the incoming air on SI engines or into the cylinder on CI engines. On SI engines, fuel injectors are located at the intake valve ports on multipoint port injector systems and upstream at the intake manifold inlet on throttle body injector systems. In a few SI engines, injectors spray directly into the combustion chamber.
  • Fuel pump: Electrically or mechanically driven pump to supply fuel from the fuel tank (reservoir) to the engine. Many modern automobiles have an electric fuel pump mounted submerged in the fuel tank. Some small engines and early automobiles had no fuel pump, relying on gravity feed.

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