CYLINDER HEAD
Cylinder head is a casting bolted to the top of the cylinder block. The cylinder head, together with the upper end of the cylinder and the top of the piston, form the combustion chamber where the fuel-air mixture burns. A cylinder head and block may be one unit.
CRANKCASE
Crankcase is a rigid frame that holds the crankshaft and the crankshaft bearings. In small engines, all or part of the crankcase may be a part of the cylinder block.
PISTON AND CONNECTING RODS
There is a piston fitted in the cylinder. This piston is connected to a connecting rod which in turn is connected to the crank shaft. When the fuel-air mixture burns, the expanding gases exert a force on the piston. This force is then transmitted through a connecting rod to the crankshaft. The piston has two to six rings to prevent the gases from escaping and to keep lubricating oil from getting into the combustion chamber.
CRANK SHAFT
Crankshaft changes the reciprocating motion of the pistons into rotary motion. The crankshaft has a number of cranks, or throws. These cranks are displaced at angles to each other. For example, in a six-cylinder, in-line, four-stroke cycle engine, the cranks are displaced at 120° angles to each other. As a result, the engine delivers three equally spaced power strokes in each revolution of the crankshaft to assure smooth operation.FLYWHEEL
Flywheel stores energy during a piston's power stroke and releases it during other strokes. This helps to keep the crankshaft turning at a constant speed
VALVES
In a four-stroke cycle engine, each cylinder has one or two intake valves, to let the air-fuel mixture into the combustion chamber, and one or two exhaust valves, to let the burned gases escape. These are called poppet valves, because they pop up and down as they open and close. The opening in the cylinder block or head uncovered by the valve is called the port. In many two-stroke cycle engines, the movement of the piston takes the place of separate valves. As the piston moves, it covers and uncovers the ports.
CAMSHAFT
Camshaft opens and closes the valves at the proper point in the engine cycle. It runs the length of the engine and has one cam (lobe) at each intake and exhaust valve. In a four-stroke cycle engine, the camshaft is geared to the crankshaft so that it runs at half the crankshaft's speed. The camshaft may be located in the head of an overhead valve engine, or in the crankcase.
FUEL SYSTEM
Fuel system includes : (1) a storage tank for petrol, (2) fuel lines to carry the petrol to the carburettor, (3) a carburettor to mix the petrol with air, and (4) an intake manifold to distribute the fuel-air mixture to the cylinders. The fuel system also includes a filter to clean dirt out of the fuel and an air cleaner to take dirt out of the air that is mixed with the petrol. In addition, the system may include a governor to limit the engine's speed.
EXHAUST SYSTEM
Exhaust system consists of one or more parts. It may include (1) an exhaust manifold to collect the burned gases from the cylinders, (2) an exhaust pipe to carry the burned gases, and (3) a silencer to silence the noise of the exhaust gases.
IGNITION SYSTEM
Ignition system is the electrical circuit necessary to set fire to, or ignite, the fuel-air mixture in the different cylinders at different times. In a car a storage battery provides electric current, which is increased in voltage by an induction coil. The high-voltage current is carried through a distributor, which delivers the electricity to each cylinder at about the moment the piston reaches the top of the compression stroke. There the electric current jumps a gap between two terminals and sets fire to the petrol-air mixture. The terminals are encased in insulating material and called a spark plug.
Some car engines have an electronic ignition system. These systems use electronic parts, such as capacitors and transistors, to produce the ignition voltage and to control it. Electronic ignition systems may use a distributor to deliver the electricity to each cylinder, or the electricity may be delivered directly to the cylinders. Electronic systems require less maintenance than do ordinary systems, and they provide better engine performance.
LUBRICATION SYSTEM
Lubrication system provides oil as a film between the moving parts of the engine to prevent wear from friction and to keep the engine cool. The two common types of four-stroke cycle engine lubrication systems are the wet sump and the dry sump. In the wet-sump engine, the oil supply is contained within the engine, in the bottom of the crankcase. In the dry-sump engine, the oil supply is contained in a separate oil tank.
Some two-stroke cycle engines, such as those used on lawn mowers, motorcycles, and boats, have no separate lubrication system. Users of these engines mix a small amount of lubricating oil with the petrol. Larger heavy-duty two-stroke cycle engines have lubrication systems similar to those on four-stroke cycle engines.
