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Components of Internal Combustion Engine.

The components of an I.C. Engine are:


A cylinder is a round hole th rough the block, bored to receive a piston. All automobile engines, whether water-cooled or air-cooled, four cycle or two cycle, have more than one cylinder. These multiple cylinders are arranged in-line, opposed, or in a V. Engines for other purposes, such as aviation, are arranged in other assorted forms. The first four cylinder engine with a sliding transmission was in the 1907 Buick.


The cylinder head is the metal part of the engine that encloses and covers the cylinders. Bolted on to the top of the block, the cylinder head contains combustion chambers, water jackets and valves (in overhead-valve engines). The head gasket seals the passages within the head-block connection, and seals the cylinders as well. Henry Ford sold his first production car, a 2-cylinder Model A, on July 23, 1903.


The piston converts the potential energy of the fuel, into the kinetic energy that turns the crankshaft. The piston is a cylindrical shaped hollow part that moves up and down inside the engine's cylinder. It has grooves around its perimeter near the top where rings are placed. The piston fits snugly in the cylinder. The piston rings are used to ensure a snug "air tight" fit.

The piston requires four strokes (two up and two down) to do its job. The first is the intake stroke. This is a downward stroke to fill the cylinder with a fuel and air mixture. The second is an upward stroke to compress the mixture. Right before the piston reaches its maximum height in the cylinder, the spark plug fires and ignites the fuel. This action causes the piston to make its third stroke (downward). The third stroke is the power stroke; it is this stroke that powers the engine. On the fourth stroke, the burned gases are sent out through the exhaust system.

The wrist pin connects the piston to the connecting rod. The connecting rod comes up through the bottom of the piston. The wrist pin is inserted into a hole (about half way up) that goes through the side of the piston, where it is attached to the connecting rod.

Pistons are made of aluminum, because it is light and a good heat conductor. Pistons perform several functions. Pistons transmit the driving force of combustion to the crankshaft. This causes the crankshaft to rotate. The piston also acts as a moveable gas-tight plug that keeps the combustion in the cylinder. The piston acts as a bearing for the small end of the connecting-rod. Its toughest job is to get rid of some of the heat from combustion, and send it elsewhere.

The piston head or "crown" is the top surface against which the explosive force is exerted. It may be flat, concave, convex or any one of a great variety of shapes to promote turbulence or help control combustion. In some, a narrow groove is cut into the piston above the top ring to serve as a "heat dam" to reduce the amount of heat reaching the top ring.


The oil pump is used to force pressurized oil to the various parts of the engine. Gear and rotary pumps are the most common types of pumps. The gear pump consists of a driven spur gear and a driving gear that is attached to a shaft driven by the camshaft. The two gears are the same size and fit snugly in the pump body. Oil is carried from the inlet to the delivery side of the pump by the opposite teeth of both gears. Here it is forced into the delivery pipe. It can't flow back, because the space between the meshing gear teeth is too tight.

The rotary pump is driven by the camshaft. The inner rotor is shaped like a cross with rounded points that fit into the star shape of the outer rotor. The inner rotor is driven by a shaft turned by the camshaft. When it turns, its rounded points "walk" around the star shaped outer rotor and force the oil out to the delivery pipe.


Oil seals are rubber and metal composite items. They are generally mounted at the end of shafts. They are used to keep fluids, such as oil, transmission fluid, and power steering fluid inside the object they are sealing. These seals flex to hold a tight fit around the shaft that comes out of the housing, and don't allow any fluid to pass. Oil seals are common points of leakage and can usually be replaced fairly inexpensively. However, the placement of some seals make them very difficult to access, which makes for a hefty labor charge!


The engine oil dip stick is a long metal rod that goes into the oil sump. The purpose of the dip stick is to check how much oil is in the engine. The dip stick is held in a tube; the end of the tube extends into the oil sump. It has measurement markings on it. If you pull it out, you can see whether you have enough oil, or whether you need more by the level of oil on the markings.


The oil filler cap is a plastic or metal cap that covers an opening into the valve cover. It allows you to add oil when the dipstick indicates that you need it. Some cars have the crankcase vented through the filler cap. Oil which is added through the filler passes down through openings in the head into the oil sump at the bottom of the engine.


Oil filters are placed in the engine's oil system to strain dirt and abrasive materials out of the oil. The oil filter cannot remove things that dilute the oil, such as gasoline and acids. Removing the solid material does help cut down on the possibility of acids forming. Removing the "grit" reduces the wear on the engine parts.

Modern passenger car engines use the "full flow" type of oil filters. With this type of filter, all of the oil passes through the filter before it reaches the engine bearings. If a filter becomes clogged, a bypass valve allows oil to continue to reach the bearings. The most common type of oil filter is a cartridge type. Oil filters are disposable; at prescribed intervals, this filter is removed, replaced and thrown away. Most states now require that oil filters be drained completely before disposal, which adds to the cost of an oil change, but helps to reduce pollution.


Within the engine is a variety of pathways for oil to be sent to moving parts. These pathways are designed to deliver the same pressure of fresh lubricating oil to all parts. If the pathways become clogged, the affected parts will lock together. This usually destroys parts that are not lubricated, and often ruins the entire engine.

The oil passages are cleverly drilled into the connecting parts of the engine, which allows the highly mobile ones (like the pistons) to have ample lubrication. Originating at the oil pump, they flow through all of the major components of the engine. In the case of the pistons and rods, the passages are designed to open each time the holes in the crankshaft and rods align.


At the bottom of the crankcase is the container containing the lifeblood of the engine. Usually constructed of thin steel, it collects the oil as it flows down from the sides of the crankcase. The pan is shaped into a deeper section, where the oil pump is located. At the bottom of the pan is the drain plug, which is used to drain the oil. The plug is often made with a magnet in it, which collects metal fragments from the oil.


Gaskets and seals are needed in your engine to make the machined joints snug, and to prevent fluids and gasses (oil, gasoline, coolant, fuel vapor, exhaust, etc.) from leaking. The cylinder head has to keep the water in the cooling system at the same time as it contains the combustion pressure. Gaskets made of steel, copper and asbestos are used between the cylinder head and engine block. Because the engine expands and contracts with heating and cooling, it is easy for joints to leak, so the gaskets have to be soft and "springy" enough to adapt to expansion and contraction. They also have to make up for any irregularities in the connecting parts.


The crankshaft converts the up and down (reciprocating) motion of the pistons into a turning (rotary) motion. It provides the turning motion for the wheels. It works much like the pedals of a bicycle, converting up-down motion into rotational motion. The crankshaft is usually either alloy steel or cast iron. The crankshaft is connected to the pistons by the connecting-rods.

Some parts of the shaft do not move up and down; they rotate in the stationary main bearings. These parts are known as journals. There are usually three journals in a four cylinder engine.


The crankshaft is held in place by a series of main bearings. The largest number of main bearings a crankshaft can have is one more than the number of cylinders, but it can have one less bearing than the number of cylinders.

Not only do the bearings support the crankshaft, but one bearing must control the forward-backward movement of the crankshaft. This bearing rubs against a ground surface of the main journal, and is called the "thrust bearing."


The connecting rod links the piston to the crankshaft. The upper end has a hole in it for the piston wrist pin and the lower end (big end) attaches to the crankshaft. Connecting rods are usually made of alloy steel, although some are made of aluminum.


Connecting rod bearings are inserts that fit into the connecting rod's lower end and ride on the journals of the crankshaft.


The valve-in-head engine has pushrods that extend upward from the cam followers to rocker arms mounted on the cylinder head that contact the valve stems and transmit the motion produced by the cam profile to the valves. Clearance (usually termed tappet clearance) must be maintained between the ends of the valve stems and the lifter mechanism to assure proper closing of the valves when the engine temperature changes. This is done by providing pushrod length adjustment or by the use of hydraulic lifters.

Noisy and erratic valve operation can be eliminated with entirely mechanical valve lifter linkage only if the tappet clearance between the rocker arms and the valve stems is closely maintained at the specified value for the engine as measured with a thickness gauge. Hydraulic valve lifters, now commonly used on automobile engines, eliminate the need for periodic adjustment of clearance.

The hydraulic lifter comprises a cam follower that is moved up and down by contact with the cam profile, and an inner bore into which the valve lifter is closely fitted and retained by a spring clip. The valve lifter, in turn, is a cup closed at the top by a freely moving cylindrical plug that has a socket at the top to fit the lower end of the pushrod. This plug is pushed upward by a light spring that is merely capable of taking up the clearance between the valve stem and the rocker arm. A small hole is drilled in the bottom of the valve-lifter cup to admit lubricating oil that enters the cam follower from the engine lubricating system through a passage in the cylinder block. A small steel ball serves as a check valve to admit the oil into the valve-fitter cup but prevent its escape. When the clearance in the entire linkage between the cam profile and the valve stem is being taken up by the spring in the valve lifter, oil flows into the lifter chamber past the ball check and is trapped there to maintain this no-clearance condition as the engine operates. Expansion or contraction of the valve linkage is compensated by oil seepage from the lifter to correct for expansion of parts and oil flow into the chamber if clearance tends to be produced between the pushrod and the lifter. Complete closure of the valve is then assured at all times without tappet noise.

The intake valve must be open while the piston is descending on the intake stroke of the piston, and the exhaust valve must be open while the piston is rising on the exhaust stroke. It would seem, therefore, that the opening and closing of the two valves would occur at the appropriate top and bottom dead-center points of the crankshaft. The time required for the valves to open and close, however, and the effects of high speed on the starting and stopping of the flow of the gases requires that for optimum performance the opening events occur before the crankshaft dead-center positions and that the closing events be delayed until after dead center.

All four valve events, inlet opening, inlet closing, exhaust opening, and exhaust closing, are accordingly displaced appreciably from the top and bottom dead centers. Opening events are earlier and closing events are later to permit ramps to be incorporated in the cam profiles to allow gradual initial opening and final closing to avoid slamming of the valves. Ramps are provided to start the lift gradually and to slow the valve down before it contacts its seat. Early opening and late closure are also for the purpose of using the inertia or persistence of flow of the gases to assist in filling and emptying the cylinder.


Valves are used for two major purposes i.e. suction of fuel and for the discharge of exhaust gases. In an overhead valve (OHV) engine, the valves are mounted in the cylinder head, above the combustion chamber. Usually this type of engine has the camshaft mounted in the cylinder block, and the valves are opened and closed by push rods. Some other valves are,


Chokes perform the fuel mixture adjustments necessary to start a cold engine. When the fuel-air mixture is too cold, the engine won't start properly, or will stall out periodically. The choke when engaged (closed) the choke causes the fuel air mixture to be increased, or "enriched". The choke is a special valve placed at the mouth of the carburetor so that it partially blocks off the entering air. When the choke plate closes, the vacuum below it increases, drawing more fuel from the fuel bowl. The rich fuel mixture burns even at lower temperatures, allowing the engine to warm up.

The manual choke is a knob on the dash, usually the push-pull type, which extends from the choke on the carburetor to the instrument panel. The driver closes the choke when starting the engine. The main thing to know about a manual choke is to push it back in when the engine has reached normal operating temperature. The trouble with the manual choke is that the driver often forgets to open it fully. This results in a rich fuel mixture which causes carbon to form in the combustion chambers and on the spark plugs. To correct this problem, the automatic choke was developed.

The automatic choke relies on engine heat. The choke valve is run by a thermostat which is controlled by exhaust heat. When the engine is cold, the valve will be closed for starting. As the engine warms, the exhaust heat will gradually open the choke valve. An automatic choke depends on a thermostatic coil spring unwinding as heat is supplied. As the engine warms up, manifold heat is transmitted to the choke housing. The heat causes the bimetal spring to relax, opening the valve.

An electric heating coil in the automatic choke shortens the length of time that the choke valve is closed. As the spring unwinds, it causes the choke valve in the carburetor air horn to open. This lets more air pass into the carburetor. The coil is mounted in a well in the exhaust crossover passage of the intake manifold. Movement of the bimetal spring is relayed to the choke valve shaft by means of linkage and levers.


All gasoline engines have a throttle valve to control the volume of intake air. The amount of fuel and air that goes into the combustion chamber regulates the engine speed and, therefore, engine power. The throttle valve is linked to the accelerator (gas pedal). The throttle valve is a butterfly valve that usually consists of a disc mounted on a spindle. The disc is roughly circular, and it has the same diameter as the main air passage in the throat or "venturi".


The Exhaust Gas Recirculation (EGR) valve is used to send some of the exhaust gas back into the cylinders to reduce combustion temperature. Why would we want to do this? Nitrous oxides (nasty pollutants) form when the combustion temperature gets above 2,500 degrees F. This happens, because at such temperatures, the nitrogen in the air mixes with the oxygen to create nitrous oxides. Did you ever have two friends that were fine by themselves but just awful when they got together? Well, our good friend, the sun, is just like that. When it's sunny, the nitrous oxides from the exhaust get together with the hydrocarbons in the air to form our not-so-good friend, smog. That's when the EGR valve comesin handy.

By recirculating some of the exhaust gas back through the intake manifold to the cylinders, we can lower the combustion temperature. Lowering the combustion temperature lowers the amount of nitrous oxide produced. Consequently, less of it comes out the tail pipe.

There are two types of EGR valves. One operates through the use of a vacuum, and the other operated through the use of pressure. Both types allow the exhaust gas in to lower the combustion temperature when it gets too high.


The process of combustion forms several gases and vapors; many of them quite corrosive. Some of these gases get past the piston rings and into the crankcase. If left in the crankcase, these substances would cause all kinds of bad things (rust, corrosion, and formation of sludge), so they have to be removed. Back in the old days, they used to be dumped out into the atmosphere through a tube. Once we realized what a problem pollution was in the sixties, the PCV (Positive Crankcase Ventilation) system was developed to take the place of the old "dump tube."

The PCV system uses a hose connected between the engine and the intake manifold to draw these gases out of the engine's crankcase and back into the cylinders to burn with the regular fuel. The only problem to solve is how to keep these gases from going willy-nilly into the manifold and upsetting the required air-fuel ratio. The solution to this problem is the PCV valve.

The PCV valve controls the release of crankcase gases and vapors to the intake manifold. The valve is kept closed by spring action when the engine is at rest. When the engine is running normally, the low vacuum it creates allows the valve to open and release crankcase vapors and gases into the intake manifold for burning. If the engine is idling or you are slowing down, the vacuum level rises and pulls the valve plunger into the valve opening. This partially blocks off the opening so that only a small amount of vapors and gases can be drawn into the intake manifold.

One really comforting feature of the PCV valve is its behavior in the event of a backfire. If your car backfires in the manifold, the pressure makes the spring close the valve completely. With the valve closed, there is no chance that the flame can move into the crankcase and cause an explosion.


The part of a machine used to provide a repetitive straight-line or back-and-forth motion to a second part, known as the follower. Cams are used to open and close the inlet and exhaust valves of a motor car engine, to index parts of automatic machinery for mass production, and to operate a sequence of control switches in electrical equipment and many other machines. Complex cam shapes may be required to produce a desired motion.

Three types of cams are in common use, the most common being the disc cam illustrated in Fig. a. The cam profile here is cut from a disc mounted on a rotating shaft. The follower can be a flat plate moving vertically in a straight line, or it can be a roller or knife-edge that moves in a straight line or is pivoted. The follower is usually spring loaded to retain contact with the cam. The second type of cam commonly used is the cylinder cam shown in Fig. b, the follower in which is a pivoted roller moving along a groove cut into a cylindrical cam rotor. The third type is the translation cam shown in Fig. c, in which the required profile that defines the motion is cut into a flat plate that moves back and forth. The follower shown in Fig. a is a spring-loaded knife edge that moves up and down. It can be observed from the figures that the motion of the follower can be changed easily, in order to obtain a desired sequence, by altering the shape of the cam profile.


Some engines have the camshaft mounted above, or over, the cylinder head instead of inside the block (OHC "overhead camshaft" engines). This arrangement has the advantage of eliminating the added weight of the rocker arms and push rods; this weight can sometimes make the valves "float" when you are moving at high speeds. The rocker arm setup is operated by the camshaft lobe rubbing directly on the rocker. Stem to rocker clearance is maintained with a hydraulic valve lash adjuster for "zero" clearance. The overhead camshaft is also something that we think of as a relatively new development, but it's not. In 1898 the Wilkinson Motor Car Company introduced the same feature on a car.


The double overhead cam shaft (DOHC) is the same as the overhead camshaft, except that there are two camshafts instead of one.


The purpose of the carburetor is to supply and meter the mixture of fuel vapor and air in relation to the load and speed of the engine. Because of engine temperature, speed, and load, perfect carburetion is very hard to obtain.

The carburetor supplies a small amount of a very rich fuel mixture when the engine is cold and running at idle. With the throttle plate closed and air from the air cleaner limited by the closed choke plate, engine suction is amplified at the idle-circuit nozzle. This vacuum draws a thick spray of gasoline through the nozzle from the full float bowl, whose fuel line is closed by the float-supported needle valve. More fuel is provided when the gas pedal is depressed for acceleration. The pedal linkage opens the throttle plate and the choke plate to send air rushing through the barrel. The linkage also depresses the accelerator pump, providing added gasoline through the accelerator-circuit nozzle. As air passes through the narrow center of the barrel, called the "venturi", it produces suction that draws spray from the cruising-circuit nozzle. The float-bowl level drops and causes the float to tip and the needle valve to open the fuel line.

To cause a liquid to flow, there must be a high pressure area (which in this case is atmospheric pressure) and a low pressure area. Low pressure is less than atmospheric pressure. The average person refers to a low pressure area as a vacuum. Since the atmospheric pressure is already present, a low pressure area can be created by air or liquid flowing through a venturi. The downward motion of the piston also creates a low pressure area, so air and gasoline are drawn through the carburetor and into the engine by suction created as the piston moves down, creating a partial vacuum in the cylinder. Differences between low pressure within the cylinder and atmospheric pressure outside of the carburetor causes air and fuel to flow into the cylinder from the carburetor.


The ignition distributor makes and breaks the primary ignition circuit. It also distributes high tension current to the proper spark plug at the correct time. The distributor is driven at one half crankshaft speed on four cycle engines. It is driven by the camshaft. Distributor construction varies with the manufacturers, but the standard model is made of a housing into which the distributor shaft and centrifugal weight assembly are fitted with bearings. In most cases, these bearings are bronze bushings.

In standard ignition, the contact set is attached to the movable breaker plate. A vacuum advance unit attached to the distributor housing is mounted under the breaker plate. The rotor covers the centrifugal advance mechanism, which consists of a cam actuated by two centrifugal weights. As the breaker cam rotates, each lobe passes under the rubbing block, causing the breaker points to open. Since the points are in series with the primary winding of the ignition coil, current will pass through that circuit when the points close. When the points open, the magnetic field in the coil collapses and a high tension voltage is induced in the secondary windings of the coil by the movement of the magnetic field through the secondary windings.

The design is to provide one lobe on the breaker cam for each cylinder of the engine; i.e., a six cylinder engine will have a six lobe cam in the distributor; and an eight cylinder engine will have an eight lobe cam, so every revolution of the breaker came will produce one spark for each cylinder of the engine. However, on a four cycle engine, each cylinder fires every other revolution so the distributor shaft must revolve at one half crankshaft speed. After the high tension surge is produced in the ignition coil by the opening of the breaker points, the current passes from the coil to the center terminal of the distributor cap. From there, it passes down to the rotor mounted on the distributor shaft and revolves with it. The current passes along the rotor, and jumps the tiny gap to the cap electrode under which the rotor is positioned at that instant. This cap electrode is connected by high tension wiring to the spark plug. As the rotor continues to rotate, it distributes current to each of the cap terminals in turn.


The coil is a compact, electrical transformer that boosts the battery's 12 volts to as high as 20,000 volts. The incoming 12 volts of electricity pass through a primary winding of about 200 turns of copper wire that raises the power to about 250 volts. Inside the distributor, this low-voltage circuit is continuously broken by the opening and closing of the points, each interruption causing a breakdown in the coil's electromagnetic field. Each time the field collapses, a surge of electricity passes to a secondary winding made up of more than a mile of hair-like wire twisted into 25,000 turns. At this point, the current is boosted to the high voltage needed for ignition and is then relayed to the rotor.


A spark plug is a device, inserted into the combustion chamber of an engine, containing a side electrode and insulated center electrode spaced to provide a gap for firing an electrical spark to ignite air-fuel mixtures.

The high-voltage burst from the coil via the distributor is received at the spark plug's terminal and conducted down a center electrode protected by a porcelain insulator. At the bottom of the plug, which projects into the cylinder, the voltage must be powerful enough to jump a gap between the center and side electrodes through a thick atmosphere of fuel mixture. When the spark bridges the gap, it ignites the fuel in the cylinder.


The spark plug wire carries 20,000 or more volts from the distributor cap to the spark plug. Spark plug wires are made of various layers of materials. The fiber core, inside the spark plug wire carries the high voltage. The older design of spark plug wires used a metallic wire to carry the high voltage. This caused electrical interference with the radio and TV reception. Some spark plug wires have a locking connection at the distributor cap. The distributor cap must first be removed and the terminals be squeezed together, and then the spark plug wire can be removed from the distributor cap.

To reduce interference with radio and TV reception, ignition systems are provided with resistance in the secondary circuit. Resistor spark plugs or special resistor type ignition cable may be used.

To work effectively in modern ignition systems, it is important that the resistor ignition cable is capable of producing a specifically designed resistance. The cable must also have enough insulation so that it can withstand heat, cold, moisture, oil, grease, and chafing. High tension electricity passing through a cable builds up a surrounding electrical field. The electrical field frees oxygen in the surrounding air to form ozone, which will attach to the rubber insulation if it is not properly protected. Ozone causes the rubber to deteriorate and lose its insulating qualities. Electrical losses will seriously weaken the spark at the plug gap.


As the rotor rotates inside the cap, it receives the high voltage from the ignition coil, then passes it to the nearest connection, which is a metal projection in the cap, which is connected to a spark plug. The distributor cap should be checked to see that the sparks have not been arcing from point to point within the cap. The inside of the cap must be clean. The firing points should not be eroded, and the inside of the towers must be clean and free from corrosion.


A distributor rotor is designed to rotate and distribute the high tension current to the towers of the distributor cap. The firing end of the rotor, from which the high tension spark jumps to each of the cap terminals, should not be worn. Any wear will result in resistance to the high tension spark. The rotor with a worn firing end will have to be replaced.

Rotors are mounted on the upper end of the distributor shaft. In this connection, the rotor must have a snug fit on the end of the shaft. On another design, two screws are used to attach the rotor to a plate on the top of the distributor shaft. Built-in locators on the rotor, and holes in the plate, insure correct reassembly. One locator is round; the other is square.

The rotor is driven directly by the camshaft, but is "advanced" (turned) by the centrifugal advance mechanism. Advancing the spark timing allows the engine to run efficiently. A vacuum advance is also fitted on some cars for the same reason.


The car's initial source of electricity is a battery, whose most important function is to start the engine. Once the engine is running, an alternator takes over to supply the car's electrical needs and to restore energy to the battery.

A 12-volt storage battery consists of layers of positively and negatively charged lead plates that, together with their insulated separators, make up each of six two-volt cells. The cells are filled with an electricity-conducting liquid (electrolyte) that is usually two-thirds distilled water and one-third sulfuric acid. Spaces between the immersed plates provide the most exposure to the electrolyte. The interaction of the plates and the electrolyte produces chemical energy that becomes electricity when a circuit is formed between the negative and positive battery terminals.


Primary current produces a magnetic field around the coil windings. This does not occur instantly, because it takes time for the current and the magnetic field to reach maximum value. The time element is determined by the resistance of the coil winding or the length of time the distributor contacts are closed. The current does not reach the maximum because the contacts remain closed for such a short time, and more so at higher engine speeds. When the breaker points begin to open, the primary current will continue to flow. This condition in a winding is increased by means of the iron core. Without an ignition condenser, the induced voltage causing this flow of current would create an arc across the contact points and the magnetic energy would be consumed in this arc. As a result, the contact points would be burned and ignition would not occur. The "condenser" prevents the arc by making a place for the current to flow. As a result of condenser action, the magnetic field produced and continued by the current flow will quickly collapse. It is the rapid cutting out of magnetic field that induces high voltage in the secondary windings. So, if the condenser should go bad, the high voltage needed to jump the gap at the spark plugs will not be possible. This could cause a no-start condition or a driving problem.


The carburetor, despite all it advances: air bleeds, correction jets, acceleration pumps, emulsion tubes, choke mechanisms, etc., is still a compromise. The limitations of carburetor design is helping to push the industry toward fuel injection. Direct fuel injection means that the fuel is sprayed directly into the combustion chamber. The fuel injected nozzle is located in the combustion chamber.

Throttle Body injection systems locate the injector(s) within the air intake cavity, or "throttle body". Multi-point systems use one injector per cylinder, and usually locate the injectors at the mouth of the intake port.

The fuel injector is an electromechanical device that sprays and atomizes the fuel. The fuel injector is nothing more than a solenoid through which gasoline is metered. When electric current is applied to the injector coil, a magnetic field is created, which causes the armature to move upward. This action pulls a spring-loaded ball or "pintle valve" off its seat. Then, fuel under pressure can flow out of the injector nozzle. The shape of the pintle valve causes the fuel to be sprayed in a cone-shaped pattern. When the injector is de-energized, the spring pushes the ball onto its seat, stopping the flow of fuel.


Mechanical fuel injection is the oldest of the fuel injection systems. It uses a throttle linkage and a governor. It is now used mainly on diesel engines. Hydraulic fuel injection is used by some of the imports. Hydraulic pressure is applied to a fuel distributor as a switching device to route fuel to a specific injector. The fuel from the tank is carried under pressure to the fuel injector(s) by an electric fuel pump, which is located in or near the fuel tank. All excess is returned to the fuel tank.


The principle of electronic fuel injection is very simple. Injectors are opened not by the pressure of the fuel in the delivery lines, but by solenoids operated by an electronic control unit. Since the fuel has no resistance to overcome, other than insignificant friction losses, the pump pressure can be set at very low values, consistent with the limits of obtaining full atomization with the type of injectors used. The amount of fuel to be injected is determined by the control unit on the basis of information fed into it about the engine's operating conditions.

This information will include manifold pressure, accelerator enrichment, cold-start requirements, idling conditions, outside temperature and barometric pressure. The systems work with constant pressure and with "variable timed" or "continuous flow" injection. Compared with mechanical injection systems, the electronic fuel injection has an impressive set of advantages. It has fewer moving parts, no need for ultra-precise machining standards, quieter operation, less power loss, a low electrical requirement, no need for special pump drives, no critical fuel filtration requirements, no surges or pulsations in the fuel line and finally, the clincher for many car makers, lower cost.


An intake manifold is a system of passages which conduct the fuel mixture from the carburetor to the intake valves of the engine. Manifold design has much to do with the efficient operation of an engine. For smooth and even operation, the fuel charge taken into each cylinder should be of the same strength and quality.

Distribution of the fuel should, therefore, be as even as possible. This depends greatly upon the design of the intake manifold. Dry fuel vapor is an ideal form of fuel charge, but present-day fuel prevents this unless the mixture is subjected to high temperature. If the fuel charge is heated too highly, the power of the engine is reduced because the heat expands the fuel charge. Therefore, it is better to have some of the fuel deposited on the walls of the cylinders and manifold vents. Manifolds in modern engines are designed so that the amount of fuel condensing on the intake manifold walls is reduced to a minimum.

In a V-8 engine, the intake manifold is mounted between the cylinder heads. The L-head engine's manifold is bolted to the side of the block, and the I-head manifold is bolted to the cylinder head.

The exhaust manifold, usually constructed of cast iron, is a pipe that conducts the exhaust gases from the combustion chambers to the exhaust pipe. It has smooth curves in it for improving the flow of exhaust. The exhaust manifold is bolted to the cylinder head, and has entrances for the air that is injected into it. It is usually located under the intake manifold. A header is a different type of manifold; it is made of separate equal-length tubes.


The ram induction manifold system consists of twin air cleaners, twin four-barrel carburetors and two manifolds containing eight long tubes of equal length (four for each manifold). This system was designed by the Chrysler Company to increase power output by in the middle speed range (1800-3600 rpm). Each manifold supplies one bank of cylinders and is carefully calculated to harness the natural supercharging effect of a ram induction system. By taking advantage of the pulsations in the air intake column caused by the valves opening and closing, sonic impulses help pack more mixture into the combustion chambers.

In the Chrysler system, the air-fuel mixture from each carburetor flows into a chamber directly below the carburetor, then passes through the long individual intake branches to the opposite cylinder bank. The right-hand carburetor supplies the air-fuel mixtures for the left-hand cylinder bank, and the left-hand carburetor supplies the right cylinder bank. The passages between the manifolds are interconnected with a pressure equalizer tube to maintain balance of the engine pulsations.


The fuel pump has three functions: to deliver enough fuel to supply the requirements of an engine under all operating conditions, to maintain enough pressure in the line between the carburetor and the pump to keep the fuel from boiling, and to prevent vapor lock. Excessive pressure can hold the carburetor float needle off its seat, causing high gasoline level in the float chamber. This will result in high gasoline consumption. The pump generally delivers a minimum of ten gallons of gasoline per hour at top engine speeds, under an operating pressure of from about 2 1/2 to 7 pounds. Highest pressure occurs at idling speed and the lowest at top speed. Although fuel pumps all work to produce the same effect, there are various types that may operate somewhat differently.


The mechanical fuel pump differs in that it has a vacuum booster section. The vacuum section is operated by the fuel pump arm; otherwise, it has nothing to do with the fuel system. During the suction (or first) stroke, the rotation of the eccentric on the camshaft puts the pump operating arm into motion, pulling the lever and diaphragm down against the pressure of the diaphragm spring and producing suction (vacuum) in the pump chamber. The suction will hold the outlet valve closed and pull the inlet valve open, causing fuel to flow through the filter screen and down through the inlet valve of the pump chamber.

During the return stroke, the diaphragm is forced up by the diaphragm spring, the inlet valve closes and the outlet valve opens to allow fuel to flow through the outlet to the carburetor. The operating lever is hinged to the pump arm, so that it can move down but cannot be raised by the pump arm. The pump arm spring forces the arm to follow the cam without moving the lever. The lever can only be moved upward by the diaphragm spring. This process causes fuel to be delivered to the carburetor only when the fuel pressure in the outlet is less than the pressure maintained by the diaphragm spring. This happens when the passage of fuel from the pump into the carburetor float chamber is open and the float needle is not seated.


Electric fuel pumps have been used for many years on trucks, buses and heavy equipment, and they have also been used as replacements for mechanically operated fuel pumps on automobiles, but only recently have they become part of a car's original equipment. The replacement types usually use a diaphragm arrangement like the mechanical pumps, except that it is actuated by an electrical solenoid.

The electrically driven turbine type of pump, first used on the Buick Riviera, was a great departure from the usual fuel pump design. It uses a small turbine wheel driven by a constant speed electric motor. The entire unit is located in the fuel tank and submerged in the fuel itself. This pump operates continuously when the engine is running. It keeps up a constant pressure which is capable of supplying the maximum fuel demands of the engine. When less fuel is required, the pump does not deliver at full potential, because the turbine is not a positive displacement type like the mechanical pump. Consequently, the turbine will run without pumping fuel and so, needs no means of varying fuel delivery rate like its mechanical counterpart. Since the fuel can flow past the spinning turbine blades, there is no need for pump inlet and outlet valves nor is there any need to vary its speed. A relay for the electric fuel pump is used to complete the circuit to the fuel pump. This cuts off current to the fuel pump in the event of an accident.


All modern fuel systems are fed through a pump, so the fuel tank is usually at the rear of the chassis under the trunk compartment. Some vehicles have a rear engine with the tank in the forward compartment. The fuel tank stores the excess fuel until it is needed for operation of the vehicle. The fuel tank has an inlet pipe and an outlet pipe. The outlet pipe has a fitting for fuel line connection and may be located in the top or in the side of the tank. The lower end is about one-half inch above the bottom of the tank so that collected sediment will not be flushed out into the carburetor. The bottom of the tank contains a drain plug so that tank may be drained and cleaned.

The gas tank of the early cars was placed higher than the engine. The idea was that the gas would flow down to the engine. This arrangement caused a problem when the car went uphill -- the gas flowed away from the engine.

Solution: drive up the hill backwards!


Clean fuel is important, because of the many small jets and passages in the carburetor and openings in a fuel injector. To ensure this cleanliness, fuel filters are installed in the fuel line. Fuel filters can be located at any point between the fuel tank and the carburetor. One may be in the tank itself, in the fuel pump or in the carburetor. The most common placement is between the fuel tank and a mechanical fuel pump. In this case, the fuel enters a glass bowl and passes up through the filter screen and out through an outlet. Any water or solid material which is trapped by the filter will fall to the bottom of the glass bowl where it can be easily seen and removed. Dirt particles usually come from scales of rust in the tank cars, storage tanks or drums. Water comes from condensed moisture in the fuel tanks.


Cars are equipped with fuel gauges which are operated along with the vehicle's electrical system. There are two types: the thermostatic type and the balancing coil type. The thermostatic type is made of a standing unit, located in the fuel tank, and the gauge itself (registering unit), which is located on the instrument panel. The fuel gauge used in some cars and trucks is of the electrically operated balanced coil type. These have a dash unit and a tank unit. The dash unit has two coils, spaced about 90 degrees apart, with an armature and integral pointer at the intersections of the coil axis. The dial has a scale in fractions between "Empty" and "Full". The tank unit has a housing, which encloses a rheostat, and a sliding brush which contacts the rheostat. The brush is actuated by the float arm. The movement of the float arm is controlled by the height of the fuel in the supply tank. The height of the fuel (called variations in resistance) changes the value of the dash unit coil so that the pointer indicates the amount of fuel available. A calibrated friction brake is included in the tank unit to prevent the wave motions of the fuel from fluctuating the pointer on the dash unit. Current from the battery passes through the limiting coil to the common connection between the two coils, which is the lower terminal on the dash unit. The current is then offered two paths, one through the operating coil of the dash unit and the other over the wire to the tank unit. When the tank is low or empty, the sliding brush cuts out all resistance in the tank unit. Most of the current will pass through the tank unit circuit because of the low resistance and only a small portion through the operating coil to the dash unit. As a result, this coil is not magnetized enough to move the dash unit pointer, which is then held at the "Empty" position by the limiting coil.

If the tank is partly full or full, the float rises on the surface of the fuel and moves the sliding brush over the rheostat, putting resistance in the tank unit circuit. More current will then pass through the operating coil to give a magnetic pull on the pointer, which overcomes some of the pull of the limiting coil. When the tank is full, the tank unit circuit contains the maximum resistance to the flow of the current. The operating coil will then receive its maximum current and exert pull of the pointer to give a "Full" reading. As the tank empties, the operating coil loses some of its magnetic pull and the limiting coil will still have about the same pull so that the pointer is pulled toward the lower reading. Variations in battery voltage will not cause an error in the gauge reading because its operation only depends on the difference in magnetic effect between the two coils.


Fuel lines, which connect all the units of the fuel system, are usually made of rolled steel or, sometimes, of drawn copper. Steel tubing, when used for fuel lines, is generally rust proofed by being copper or zinc plated.


In mechanical engineering it is a wheel of high mass that is attached to a rotating shaft, and serves to smooth out the delivery of torque, or turning power, from a motor or engine. The large inertia of the flywheel enables it to absorb and release energy with little variation in speed. An internal combustion engine, for example, produces power in a succession of bursts that are transmitted by the driveshaft to a flywheel, which absorbs the pulses of energy smoothly into its rotational motion, thereby imparting to the shaft a nearly steady torque.

A second function of the flywheel is to store energy in industrial operations such as forging, where high power is required only intermittently— or in applications where power is required on a standby basis or for emergencies. The flywheel first became important in industry with the invention of the steam engine in the 18th century, but its use is recorded as early as the 12th century.


The combustion chamber is where the air-fuel mixture is burned. The location of the combustion chamber is the area between the top of the piston at what is known as TDC (top dead center) and the cylinder head. TDC is the piston's position when it has reached the top of the cylinder, and the center line of the connecting rod is parallel to the cylinder walls.

The two most commonly used types of combustion chamber are the hemispherical and the wedge shape combustion chambers. The hemispherical type is so named because it resembles a hemisphere. It is compact and allows high compression with a minimum of detonation. The valves are placed on two planes, enabling the use of larger valves. This improves "breathing" in the combustion chamber. This type of chamber loses a little less heat than other types. Because the hemispherical combustion chamber is so efficient, it is often used, even though it costs more to produce.

The wedge type combustion chamber resembles a wedge in shape. It is part of the cylinder head. It is also very efficient, and more easily and cheaply produced than the hemispherical type.


A supercharger is a compressor. Hence, a supercharged engine has a higher overall compression than a nonsupercharrged engine having the same combustion chamber volume and piston displacement and will burn more fuel. Unfortunately, the increase in power is not proportional to the increase in fuel consumption. There are two general models of superchargers, the Rootes type and the centrifugal type. The Rootes "blower" has two rotors, while the centrifugal uses an impeller rotating at high speed inside a housing.

Superchargers can be placed between the throttle body of the carburetor or fuel injection system and the manifold; or at the air inlet before the throttle body. Racing cars usually have it located between the throttle body and the manifold. This design has the advantage that the fuel can be supplied through the throttle body without modification to any part of the system. If the supercharger is placed in front of the throttle body, fuel must be supplied under sufficient pressure to overcome the added air pressure created by the supercharger. The advantage of a supercharger over a turbocharger is that there is no lag time of boost; the moment the accelerator pedal is depressed, the boost is increased.


A turbocharger, or supercharger, can boost engine power up to 40%%. The idea is to force the delivery of more air-fuel mixture to the cylinders and get more power from the engine. A turbocharger is a supercharger that operates on exhaust gas from the engine.

Although turbochargers and superchargers perform the same function, the turbocharger is driven by exhaust gases, while the supercharger is driven by belts and gears. The turbocharger has a turbine and a compressor, and requires less power to be driven than a supercharger. The pressure of the hot exhaust gases cause the turbine to spin. Since the turbine is mounted on the same shaft as the compressor, the compressor is forced to spin at the same time, drawing 50%% more air into the cylinders than is drawn in without the turbocharger. This creates more power when the air-fuel mixture explodes.

A turbocharged engine's compression ratio must be lowered by using a lower compression piston, since an excessive amount of pressure will wear on the piston, connecting rods, and crankshaft, and destroy the engine. All of these parts then, as well as the transmission, must be strengthened on a turbocharged engine or it will be torn apart by the increased horsepower.


The breather is the positive crankcase ventilation system directing atmospheric pressure to the crankcase. The atmospheric pressure then pushes the blowby gases to a low pressure area. The air that is directed into the crankcase must first be filtered; if it is not, the dust and sand particles will destroy the engine parts. When there is too much blowby, it is routed back through the crankcase breather element. It then enters the carburetor or throttle body with the incoming fresh air to be burned in the cylinders. In addition, the breather helps to keep the regular air filter cleaner for a longer period of time, since blowby contains oil vapor from the crankcase.


Several fuel pumps have a vacuum booster section that operates the windshield wipers at an almost constant speed. The fuel section then functions in the same way as ordinary fuel pumps. One difference is that the rotation of the camshaft eccentric in the vacuum pump also operates the vacuum booster section by actuating the pump arm, which pushes a link and the bellows diaphragm assembly upward, expelling air in the upper chamber through its exhaust valve out into the intake manifold. On the return stroke of the pump arm, the diaphragm spring moves the bellows diaphragm down, producing a suction in the vacuum chamber. The suction opens the intake valve of the vacuum section and draws air through the inlet pipe from the windshield wipers.

When the wipers are not operating, the intake manifold suction (vacuum) holds the diaphragm up against the diaphragm spring pressure so that the diaphragm does not function with every stroke of the pump arm. When the vacuum is greater than the suction produced by the pump, the air flows from the windshield wiper through the inlet valve and vacuum chamber of the pump and out the exhaust valve outlet to the manifold, leaving the vacuum section inoperative. With high suction in the intake manifold, the operation of the wiper will be the same as if the pump were not installed. When the suction is low, as when the engine is accelerated or operating at high speed, the suction of the pump is greater than that in the manifold and the vacuum section operates the wipers at a constant speed. Some pumps have the vacuum section located in the bottom of the pump instead of in the top, but the operation is basically the same.


The air pump sends (or pumps) compressed air into the exhaust manifold and in some cases to the catalytic converter. The oxygen in the pressurized air helps to burn quite a bit of any unburned hydrocarbons (fuel) and therby converts the poisonous carbon monoxide into good old carbon dioxide.

A belt from the engine drives the air pump. It has little vanes (thin, flat, curved fins) that draw the air into the compression chamber. Here, the air is compressed and sent off to the exhaust manifold where it speeds up the emissions burning process. Stainless steel nozzles are used to shoot the air into the exhaust manifold, because they will not burn. Some engines use a pulse air injection system. This system uses pulses of exhaust gas to operate an air pump that delivers air into the exhaust system.


Air cleaners are made to separate dust and other particles in the incoming air before it enters the carburetor. Thousands of cubic feet of air are drawn from within the car hood and passed through the engine cylinders, so it is important that the air is clean.

When driving on dirt or other dusty roads, dust particles are drawn through the radiator and find their way into the engine if it is not filtered and cleaned. Dust and other foreign materials in the engine will cause excessive wear and operating problems.


The harmonic balancer, or vibration damper, is a device connected to the crankshaft to lessen the torsional vibration. When the cylinders fire, power gets transmitted through the crankshaft. The front of the crankshaft takes the brunt of this power, so it often moves before the rear of the crankshaft. This causes a twisting motion. Then, when the power is removed from the front, the halfway twisted shaft unwinds and snaps back in the opposite direction. Although this unwinding process is quite small, it causes "torsional vibration." To prevent this vibration, a harmonic balancer is attached to the front part of the crankshaft that's causing all the trouble. The balancer is made of two pieces connected by rubber plugs, spring loaded friction discs, or both.

When the power from the cylinder hits the front of the crankshaft, it tries to twist the heavy part of the damper, but ends up twisting the rubber or discs connecting the two parts of the damper. The front of the crank can't speed up as much with the damper attached; the force is used to twist the rubber and speed up the damper wheel. This keeps the crankshaft operation calm.


A recent development is the serpentine belt, so named because they wind around all of the pulleys driven by the crankshaft pulley. This design saves space, but if it breaks, everything it drives comes to a stop.


The automobile engine uses a metal timing chain, or a flexible toothed timing belt to rotate the camshaft. The timing chain/belt is driven by the crankshaft. The timing chain, or timing belt is used to "time" the opening and closing of the valves. The camshaft rotates once for every two rotations of the crankshaft.


A metering rod varies the size of the carburetor jet opening. Fuel from the float bowl is metered through the jet and the metering rod within it. The fuel is forced from the jet to the nozzle extending into the venturi. As the throttle valve is opened, its linkage raises the metering rod from the jet. The rod has several steps, or tapers, on the lower end. As it is raised in the jet, it makes the opening of the jet greater in size. This allows more fuel to flow through the jet to the discharge nozzle. The metering must keep pace with the slightest change in the throttle valve position so that the correct air-fuel mixture is obtained in spite of engine speed.


The radiator is a device designed to dissipate the heat which the coolant has absorbed from the engine. It is constructed to hold a large amount of water in tubes or passages which provide a large area in contact with the atmosphere. It usually consists of a radiator core, with its water-carrying tubes and large cooling area, which are connected to a receiving tank (end cap) at the top and to a dispensing tank at the bottom. Side flow radiators have their "endcaps" on the sides, which allows a lower hood line.

In operation, water is pumped from the engine to the top (receiving) tank, where it spreads over the tops of the tubes. As the water passes down through the tubes, it loses its heat to the airstream which passes around the outside of the tubes. To help spread the heated water over the top of all the tubes, a baffle plate is often placed in the upper tank, directly under the inlet hose from the engine.


The reason the coolant goes into the radiator is to allow air to pass through it and cool the coolant. When you are driving fast enough, the air rushes through the grille of the car and passes through the radiator core. If you aren't driving fast enough to push air through the radiator, then the fan will pull the air through.

The fan improves cooling when you are driving at slow speeds, or if the engine is idling. It is usually mounted on the water pump shaft, and is turned by the same belt that drives the water pump and the alternator, although it can be mounted as an independent unit. Most independently mounted fans are electric.