This section will cover the basic components associated with the automotive engine compartment and the internal combustion engine. Internal combustion means the fuel, which is a mixture of gasoline and air, burns inside of the engine in the combustion chambers. Air enters the engine through the air cleaner and proceeds to the throttle plate. You control the amount of air that passes through the throttle plate and into the engine with the gas pedal. It is then distributed through the intake manifold, to each cylinder. Fuel is added to the air-stream by either a fuel injection system or, in older vehicles, by the carburetor. The majority of engines in motor vehicles today are four-stroke internal combustion engines.

Engine Types

There are several engine types which are identified by the number of cylinders and the way the cylinders are laid out. Motor vehicles will have from 3 to 12 cylinders which are arranged in the engine block in several configurations. In-line engines have their cylinders arranged in a row. The "V" arrangement uses two banks of cylinders side-by-side and is commonly used in V-6, V-8, V-10 and V-12 configurations. Flat engines use two opposing banks of cylinders and are less common than the other two designs.

Each cylinder contains a piston that travels up and down inside the cylinder. All the pistons in the engine are connected through individual connecting rods to a common crankshaft. A cylinder head is bolted to the top of each bank of cylinders to seal the individual cylinders and contain the combustion process that takes place inside the cylinder. The cylinder head contains at least one intake valve and one exhaust valve for each cylinder. This allows the air-fuel mixture to enter the cylinder and the burned exhaust gas to exit the cylinder. Most engines have two valves per cylinder, one intake valve and one exhaust valve. Some newer engines are using multiple intake and exhaust valves per cylinder for increased engine power and efficiency. These engines are sometimes named for the number of valves that they have such as "24 Valve V6" which indicates a V-6 engine with four valves per cylinder. Modern engine designs can use anywhere from 2 to 5 valves per cylinder. The valves are opened and closed by means of a camshaft. A camshaft is a rotating shaft that has individual lobes for each valve. The lobe is a "bump" on one side of the shaft that pushes against a valve lifter moving it up and down. When the lobe pushes against the lifter, the lifter in turn pushes the valve open. When the lobe rotates away from the lifter, the valve is closed by a spring that is attached to the valve. The camshaft must be synchronized with the crankshaft so that it makes one revolution for every two revolutions of the crankshaft. In most engines, this is done by a Timing Chain that connect the camshaft with the crankshaft. Newer engines have the camshaft located in the cylinder head directly over the valves. It also requires much longer timing chains or timing belts which are prone to wear. Some engines have two camshafts on each head, one for the intake valves and one for the exhaust valves. These engines are called Double Overhead Camshaft (D.O.H.C.) Engines while the other type is called Single Overhead Camshaft (S.O.H.C.) Engines. Engines with the camshaft in the block are called Overhead Valve (O.H.V) Engines.

How 4 stroke engines work

4 stroke engines typically have valves at the top of the combustion chamber. The simplest type has one intake and one exhaust valve. More complex engines have two of one and one of the other, or two of each. So when you see "16v" emblem on the back of a car, it means it's a 4-cylinder engine with 4 valves per cylinder - two intake and two exhaust - thus 16 valves, or "16v". The valves are opened and closed by a rotating camshaft at the top of the engine. The camshaft is driven by either gears directly from the crank, or more commonly by a timing belt.
As the piston retreats on the first stroke, the intake valve is opened and the fuel-air mixture is sucked into the combustion chamber. The valve closes as the piston bottoms out. As the piston begins to advance, it compresses the fuel-air mix. As it reaches the top of it's stroke, the spark plug ignites the fuel-air mix and it burns. The expanding gasses force the piston back down on its second stroke. At the bottom of this stroke, the exhaust valve opens, and as the piston advances for a second time, it forces the spent gasses out of the exhaust port. As the piston begins to retreat again, the cycle starts over, sucking a fresh charge of fuel-air mix into the combustion chamber.

4 stroke Diesel Engines

Mechanically, 4 stroke diesel engines work identically to four-stroke gasoline engines in terms of piston movement and crank rotation. It's in the combustion cycle where the differences come through. First, during the intake cycle, the engine only sucks air into the combustion chamber through the intake valve - not a fuel/air mix. Second, there is no spark plug. Diesel engines work on self-ignition, or detonation. At the top of the compression stroke, the air is highly compressed, and very hot (around 700 °C - 1292°F). The fuel is injected directly into that environment and because of the heat and pressure, it spontaneously combusts (this system is known as direct-injection).

One other component that some diesel engines have is a glow plug. From cold, some lower-tech engines can't retard the ignition enough, or get the air temperature high enough on startup for the spontaneous combustion to happen. In those engines, the glow plug is literally a hot wire in the top of the cylinder designed to increase the temperature of the compressed air to the point where the fuel will combust. These engines typically have a pictograph on the dashboard that looks like a light bulb. When starting the engine cold, you need to wait for that light to go out - basically you're waiting for the glow plugs to get up to temperature. In really old diesel designs, this could be as long as 10 seconds. Nowadays it's nearly instantaneous, or in the case of advanced ECM systems, not needed at all.

Interference vs. Non-Interference Engines

It's worth mentioning the two sub-types of 4 stroke engine at this point. Because the valves always open inwards, into the combustion chamber, they take up some space at the top of the chamber. In an interference engine, the position of the piston at the top of its stroke will occupy the same physical space that the open valves do whilst the piston is at the bottom of its stroke. It's important to know if your engine is an interference engine because if the timing belt breaks, at least one set of valves will stop in the open position and the momentum of the engine will ram the piston in that cylinder up into the valves requiring a very expensive engine repair or replacement. In a non-interference engine, the valves do not occupy any space that the piston could move into, so if your timing belt snaps on one of these engines, in 99% of cases you won't suffer any valve damage because the piston cannot physically touch the open valves. That is the technical explanation of why its important to get your timing belt changed at the manufacturer-specified mileage.

How an Engine Works

The four strokes are Intake, Compression, Power and Exhaust. The piston travels down on the Intake stroke, up on the Compression stroke, down on the Power stroke and up on the Exhaust stroke.

Intake
As the piston starts down on the Intake stroke, the intake valve opens and the fuel-air mixture is drawn into the cylinder.
When the piston reaches the bottom of the intake stroke, the intake valve closes, trapping the air-fuel mixture in the cylinder.

Compression
The piston moves up and compresses the trapped air fuel mixture. The amount that the mixture is compressed is determined by the compression ratio of the engine. The compression ratio on the average engine is in the range of 8:1 to 10:1.
This means that when the piston reaches the top of the cylinder, the air-fuel mixture is squeezed to about one tenth of its original volume.

Power
The spark plug fires, igniting the compressed air-fuel mixture which produces a powerful explosion. The combustion process pushes the piston down the cylinder, turning the crankshaft. Each piston fires at a different time, determined by the engine firing order. By the time the crankshaft completes two revolutions, each cylinder in the engine will have gone through one power stroke.

Exhaust
With the piston at the bottom of the cylinder, the exhaust valve opens to allow the burned exhaust gas to be expelled to the exhaust system. The piston travels up to the top of the cylinder pushing the exhaust out.

The coolant enters the radiator through the top radiator hose, which is usually connected to the top of the radiator. When the liquid has cooled it leaves the radiator through the bottom radiator hose. A fan is located behind the radiator, positioned so that it can draw air through the radiator. The water pump draws the liquid from the radiator through the bottom radiator hose and sends it to the engine, where it circulates through water jackets located around the combustion chamber in the cylinder and other hot parts. On some models the timing belt drives your water pump. On other models the accessory drive belt, drives the water pump. Water circulates through passages around the cylinders and then travels through the radiator to cool it off. In a few cars the engine is air-cooled instead. If the engine were not properly cooled the extremely high temperatures created by the exploding gas would melt many of their parts. The thermostat is the only part of the cooling system that does not cool things off. Instead it helps the liquid in the coolant system warm up the engine quickly. When the thermostat senses that the liquid (coolant) is cold it shuts and doesn't allow the liquid to circulate through the radiator. Heater core is located inside the vehicle between the instrument panel and the firewall. It provides heat for the passenger compartment. The same liquid that the water pump circulates throughout the engine also circulates through the heater core when the engine is operating.

Water Pump - The water pump is a simple centrifugal pump driven by a belt connected to the crankshaft of the engine. The pump circulates fluid whenever the engine is running. The fluid leaving the pump flows first through the engine block and cylinder head, then into the radiator and finally back to the pump.

Radiator - A radiator is a type of heat exchanger. It is designed to transfer heat from the hot coolant that flows through it to the air blown through it by the fan. Most modern cars use aluminum radiators. These radiators are made by brazing thin aluminum fins to flattened aluminum tubes. The coolant flows from the inlet to the outlet through many tubes mounted in a parallel arrangement. The fins conduct the heat from the tubes and transfer it to the air flowing through the radiator. Radiators usually have a tank on each side, and inside the tank is a transmission cooler. The transmission cooler is like a radiator within a radiator, except instead of exchanging heat with the air, the oil exchanges heat with the coolant in the radiator.

Fan - Like the thermostat, the cooling fan has to be controlled so that it allows the engine to maintain a constant temperature. Front-wheel drive cars have electric fans because the engine is usually mounted transversely, meaning the output of the engine points toward the side of the car. The fans are controlled either with a thermostatic switch or by the engine computer, and they turn on when the temperature of the coolant goes above a set point. They turn back off when the temperature drops below that point.

NOTE: Older car radiators had belt-driven fans that spun behind the radiator as fast as the engine was spinning. The fan is there to draw the warm air away from the back of the radiator to help it to work efficiently. With the old way of doing it was that the fan ran all the time the engine was running and stopped when the engine stopped, this was a problem. This meant that the radiator was having air drawn through it at the same rate in freezing cold conditions as it was on a hot day and when you parked the car, the radiator basically cooked because it had no airflow while it was cooling down. In newer model vehicles, the radiator fan is electric and is activated by a temperature sensor in the coolant. When the temperature gets above a certain level, the fan comes on, which can happen even once you've stopped the engine. This is why sometimes on a hot day, even when you park the car and turn off the engine, the radiator fan is still going.

THERMOSTAT - Its function is to control the operating temperature of the engine. The thermostat is a small device that normally sits in the system in-line to the radiator. It is a spring-loaded valve actuated by a bimetallic spring, so the hotter it gets, the wider open the valve is. When you start the engine, the thermostat is cold and so it's closed. This redirects the flow of coolant back into the engine and bypasses the radiator completely but because the interior heater radiator is on a separate circuit, the coolant is allowed to flow through it. It has a much smaller surface area and its cooling effect is nowhere near as great. This allows the engine to build up heat quite quickly. As the coolant heats up, the thermostat begins to open and the coolant is allowed to pass out to the radiator where it dumps heat out into the air before returning to the engine block. Once the engine is fully hot, the coolant is at operating temperature and the thermostat is permanently open, redirecting almost all the coolant flow through the radiator.

Heating System

You may have heard the advice that if you car is overheating, open all the windows and run the heater with the fan going at full blast. This is because the heating system is actually a secondary cooling system that mirrors the main cooling system on your car. The heater core, which is located in the dashboard of your car, is really a small radiator. The heater fan blows air through the heater core and into the passenger compartment of your car. The heater core draws its hot coolant from the cylinder head and returns it to the pump -- so the heater works regardless of whether the thermostat is open or closed.

Air Cooling

You don't see this much on car engines at all now. It is still used a lot on motorbike engines because it's a very simple method of cooling. For air cooling to work, you need two things - fins (lots of them) and good airflow. An air-cooled engine is normally easy to spot because of the fins built into the outside of the cylinders. The idea is simple - the fins act as heat sinks, getting hot with the engine but transferring the heat to the air as the air passes through and between them. Air-cooled engines don't work particularly well in long, hot traffic jams though, because obviously there's very little air passing over the fins. They are good in the winter when the air is coldest, but that illustrates a weak spot in the whole design. Air cooled engines can't regulate the overall temperature of the cylinder heads and engine, so the temperature tends to swing up and down depending on engine load, air temperature and forward speed. A famous problem with air-cooling is associated with V-twin motorcycles. Because the rear cylinder is tucked in the frame behind the front cylinder, its supply of cool, uninterrupted air is extremely limited and so in these designs, the rear cylinder tends to run extremely hot compared to the front.

Oil Cooling

To some extent, all engines have oil-cooling. It's one of the functions of the engine oil - to transfer heat away from the moving parts and back to the sump where fins on the outside of the sump can help transfer that heat out into the air. But for some engines, the oil system itself is designed to be a more efficient cooling system. As the oil moves around the engine, at some points it's directed through cooling passageways close to the cylinder bores to pick up heat. From there it goes to an oil radiator placed out in the airflow to disperse the heat into the air before returning into the core of the engine.

Water Cooling

This is by far and away the most common method of cooling and engine down. With water cooling, a coolant mixture is pumped around pipes and passageways inside the engine separate to the oil, before passing out to a radiator. The radiator itself is made of metal, and it forces the coolant to flow through long passageways each of which have lots of metal fins attached to the outside giving a huge surface area. The coolant transfers its heat into the metal of the radiator, which in turn transfers the heat into the surround air through the fins - essentially just like the air-cooled engine fins. The coolant itself is normally a mixture of distilled water and an antifreeze component. The water needs to be distilled because if you just use tap water, all the minerals in it will deposit on the inside of the cooling system and mess it up. The antifreeze is in the mix, obviously to stop the liquid from freezing in cold weather. If it froze up, you'd have no cooling at all and the engine would overheat and weld itself together in a matter of minutes. The antifreeze mix normally also has other chemicals in it for corrosion resistance too and when mixed correctly it raises the boiling point of water, so even in the warmer months of the year, a cooling system always needs a water / antifreeze mix in it.
The coolant system in a typical car is under pressure once the engine is running, as a byproduct of the water pump and the expansion that water undergoes as it heats up. Because of the coolant mixture, the water in the cooling system can get over 100°C without boiling which is why it's never a good idea to open the radiator cap immediately after you've turned the engine off.

The Electrical System consists of a storage battery, generator, starting (cranking) motor, lighting system, ignition system, and various accessories and controls. Additional electrically operated features, such as radios, window regulators, and multi-speed windshield wipers, also added to system requirements. The 12-volt system is used in the modern automobile. In the near future, vehicle will run off a 40-volt system. The alternator is connected to the engine by a belt and generates electricity to recharge the battery. The battery makes 12-volt power available to everything in the car needing electricity through the vehicle's wiring.

ALTERNATOR - The alternator produces electricity used to maintain battery storage charge and to help run all the electrical accessories, including the ignition and the engine control systems. It is belt-driven by the engine and produces an alternating current (AC), which is converted internally to 12 volts direct current (DC) by the diode bridge or rectifiers. AC current cannot be stored, which is why cars no longer use generators. AC current is converted to DC and the electricity is stored in alternators.

BATTERY - Stores electrical energy for starting the engine and for operating electrical units when the output produced by the Generator is not sufficient. Its principle is to convert chemical energy into electrical energy. Batteries are built in a series of cells, each producing approximately 2 volts. A 6 volt Battery will the have 3 cells and a 12 volt Battery has 6 cells, all connected in series.

GENERATOR - Converts the mechanical energy, which it obtains from the Crankshaft through a pulley and belt system, into the electrical energy needed for ignition, lights and all the various electric accessories of the modern automobile. It also recharges the Battery. The Generator consists of two basic parts: the Field Coils which create the magnetic field and the Armature Winding which rotates in the magnetic field producing a flow of current. Most of the modern Generators incorporate a cooling fan which is usually part of the driving pulley.

REGULATOR - Controls the Generator's output according to the needs of the electrical system.

STARTING MOTOR (STARTER) - A special type electric motor designed to crank the engine at a speed high enough to permit it to start. It is capable of operating under heavy overload and creates great power, but only for a short time. When the Starting Motor is operating, the driving Pinion Gear, which is attached to its shaft, is thrust forward to engage the teeth of the Flywheel. The Flywheel rotates the Crankshaft to which it is mounted thus cranking the engine. As soon as the engine starts up, the driving Pinion is automatically disengaged from the Flywheel.

The Emission Control System in modern cars consists of a catalytic converter, a collection of sensors and actuators, and a computer to monitor and adjust everything. For example, the catalytic converter uses a catalyst and oxygen to burn off any unused fuel and certain other chemicals in the exhaust. An oxygen sensor in the exhaust stream makes sure there is enough oxygen available for the catalyst to work and adjusts things if necessary.

Hydrocarbons, carbon monoxide and oxides of nitrogen are created during the combustion process and are emitted into the atmosphere from the tail pipe. There are also hydrocarbons emitted as a result of vaporization of gasoline and from the crankcase of the automobile. In 1981 an oxygen sensor was installed in the exhaust system and would measure the fuel content of the exhaust stream.

Air Injection System - Since no internal combustion engine is 100% efficient, there will always be some unburned fuel in the exhaust. This increases hydrocarbon emissions. To eliminate this source of emissions an air injection system was created. The air injection system is designed to introduce outside air into the exhaust stream to assist in burning the gases produced by the engine. Air is injected into the exhaust system at one of several locations. Outside air is drawn by an air pump, a pulse air valve, or a reed valve. The air pump is run by a fan belt on the front of the engine or, in some cases, a small electric motor.
PCV Valve - The purpose of the positive crankcase ventilation (PCV) system, is to take the vapors produced in the crankcase during the normal combustion process, and redirecting them into the air/fuel intake system to be burned during combustion. The positive crankcase ventilation system keeps blowby gases from escaping from the engine.

EGR Valve - An exhaust gas recirculation system is designed to reduce nitric oxide emissions from an engine. Nitric oxide is produced when the temperature of the combustion chamber rises above 2,500 degrees Fahrenheit. The purpose of the exhaust gas recirculation valve (EGR) valve is to meter a small amount of exhaust gas into the intake system, this dilutes the air/fuel mixture so as to lower the combustion chamber temperature.

Thermostatic Air Cleaner System

This system regulates air temperature flow into the engine. The thermostatic air cleaner system is designed to draw heated air from around the exhaust manifold of the engine during a cold engine "start-up" and as the engine warms up to normal operating temperature, a valve changes position to let cool air enter the engine.

The Exhaust System in your car does two jobs, first it transfers poisonous exhaust gases from the engine to the rear of the car, and the exhaust system quiets down the engine exhaust sound while it is running. The exhaust system consists of a exhaust manifold, exhaust pipe a catalytic converter, a muffler and in some cases a secondary muffler.

The Exhaust System houses the fuel management system oxygen sensor. Usually the primary oxygen sensor is in the head pipe before the catalytic converter and the secondary sensor is behind the catalytic converter. These sensors are used to monitor the density of exhaust gases and relay information to the Powertrain Control Module (PCM). The PCM processes this information, along with several other sensor inputs that adjusts fuel air mixture accordingly.

Exhaust Systems need to be corrosion resistance do to the heat and moisture produced by the engine. The engine in your car produces water along with the exhaust gases as a natural by product of the combustion process. That is why you can see water and steam coming from the exhaust pipe when the car is cold, as the car heats up the water is vaporized quickly so you don't see the moister. moister. moister. moister. moister.

Primary Exhaust System

The function of the primary system is to transfer the exhaust from the exhaust manifold through the head pipe and flex pipe to the catalytic converter. The catalytic converter is has a heat shield mounted over to protect the floor board from the high heat the catalytic converter can produce. The exhaust system is held in place by an exhaust hanger. Most exhaust systems are made of galvanized metal so they last longer then the conventional steel systems.

Secondary Exhaust System

The secondary exhaust system is used to transfer the exhaust front the catalytic converter thought he muffler and out the rear of the vehicle through the tail pipe.

System Components

Exhaust Manifold - bolted to the cylinder head and is used to gather and transfer exhaust gases from the exhaust port of the cylinder head to the exhaust head pipe. Most exhaust manifold collect between 3 and 6 ports.

Head Pipe - the tube that connects the exhaust manifold with a exhaust flange and the other end to the catalytic converter.

Exhaust Flange - the connector union between the exhaust manifold and the head pipe.

Exhaust Pipe - the pipe that is used to connect the various components of the exhaust system.

Muffler - used to reduce the audible sound frequency developed by the engine.

Catalytic Converter - used to convert unused fuel into completely spent fuel. The catalytic converter looks like a muffler. It is located in the exhaust system ahead of the muffler. Inside the converter are pellets or a honeycomb made of platinum or palladium. As exhaust gases pass through the honeycomb or pellets contained inside the shell, a chemical reaction takes place. The platinum or palladium are used as a catalyst. As hydrocarbons or carbon monoxide in the exhaust are passed over the catalyst, it is chemically oxidized or converted to carbon dioxide and water.

Secondary Muffler - sometimes called a resonator the secondary muffler furthers the sound deadening of the engine exhaust.

Exhaust System Hanger - a metal strap connecting the exhaust system to the bottom of the car. They are usual made with a rubber insulator.

Tail Pipe - the tube that is connected to the muffler that continues to the back of the car.

The engine's Fuel System pumps gas from the gas tank and mixes it with air so that the proper air/fuel mixture can flow into the cylinders. Fuel is delivered in three common ways: carburetion, port fuel injection and direct fuel injection.

In carburetion, a device called a carburetor mixes gas into air as the air flows into the engine.

In a fuel-injected engine, the right amount of fuel is injected individually into each cylinder either right above the intake valve (port fuel injection) or directly into the cylinder (direct fuel injection).

GASOLINE

Gasoline is a distilled and refined oil product made up of hydrogen and carbons - a carcinogenic, hydrocarbon. It's designed to be relatively safe to handle, if you're careful. When you have a gasoline fire, it's not the liquid that is burns, it's the vapors, and this is the key to fueling an engine. The carburetor or fuel injectors spray gasoline into an air stream becoming a mist. The tiny particles of gasoline evaporate into a vapor extremely quickly, and combined in a cloud with the air, it becomes extremely combustible. The smaller the particles from the carburetor jet or fuel injector, the more efficiently the mixture burns.

The compression ratio of an engine is the measurement of the ratio between the combined volume of a cylinder and a combustion chamber when the piston is at the bottom of its stroke, and the same volume when the it's at the top of its stroke. The higher the compression ratio, the more mechanical energy an engine can squeeze from its air-fuel mixture. Similarly, the higher the compression ratio, the greater the likelihood of detonation.

Octane Ratings

When a fuel-air mixture, under the right conditions, can spontaneously combust. In order to control this property, all gasoline has chemicals mixed in with them to control how quickly the fuel burns. This is known as the octane rating of the fuel. The higher the rating, the slower and more controlled the fuel burns. Octane is measured relative to a mixture of isooctane and n-heptane. An 87-octane gasoline has the same knock resistance as a mixture of 87% isooctane and 13% n-heptane. The octane value of a fuel used to be controlled by the amount of tetraethyl lead in it, but in the 70s and 80s when lead was found to be harmful, lead-free gasoline appeared and other substances were introduced to control octane instead. The higher the altitude above sea level, the lower the octane requirement. Higher octane does not equal more power. Power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber. Because high performance engines operate with high compression ratios they are more likely to suffer from detonation and so to compensate, they need a higher octane fuel to control the burn.

FUEL PUMP - Operated by an off-center cam at the front end of the Camshaft. As the Camshaft rotates, the eccentric cam actuates the Pump Rocker Arm which pulls the Lever and the flexible Diaphragm upward against the pressure of the Diaphragm Spring, thus creating a vacuum in the Pump Chamber. This suction holds the Inlet Valve open making the fuel flow from the Supply Tank into the Sediment Bowl. From the Sediment Bowl, the fuel passes through a Filter where solid matter and water are trapped. Clean fuel enters through the open Inlet Valve into the Pump Chamber. On the return stroke, the Diaphragm is forced down by the Spring, the Inlet Valve closes and the Outlet Valve is forced open allowing the fuel to flow through the outlet to the Carburetor.
FUEL FILTER - Are designed to prevent metals, dirt and debris from being pushed into your engine and causing catastrophic damage. Foreign substances can be found in your vehicle's fuel tank as well as the gas station holding tank. And because these substances are heavier than liquid they tend to settle on the bottom of the tanks. So when you drive on any empty tank or are lucky enough to fill up after a fuel delivery day
In carburetor fuel filters they are plastic in-line fuel filters. They're typically designed to have the fuel sucked through them via a mechanical crank-driven fuel pump up near the carburetor. The job of an in-line fuel filter is to filter out sediment and particulates in the gasoline that might otherwise cause problems further down the line in the engine
In Fuel injection filters they are the metal canister-type fuel filters that are normally buried under the car. They're designed to have the fuel pushed through them by an electric high-pressure fuel pump, and so the pressure in the fuel line is much higher. This is why they're made of metal.
FUEL INJECTION - Electro-mechanically operated needle valves. When a current is passed through the injector electromagnetic coil, the valve opens and the fuel pressure forces petrol through the spray tip and out of the diffuser nozzle, atomizing it. When current is removed, the combination of a spring and fuel back-pressure causes the needle valve to close. This gives an audible 'tick' noise when it happens, which is why even a quiet fuel-injected engine has a soft but rapid tick-tick-tick-tick noise as the injectors fire. This on-off cycle time is known as the pulse width and varying the pulse width determines how much fuel can flow through the injectors. When you ask for more throttle either via the accelerator pedal you're opening a butterfly valve. This lets more air into the intake system and the position of the throttle is measured with a potentiometer. The engine control unit (ECU) gets a reading from this potentiometer and increases the injector pulse width to allow more fuel to be sprayed by the injectors. Downwind of the throttle body is a mass airflow sensor. This is normally a heated wire. The more air that flows past it, the quicker it dissipates heat and the more current it needs to remain warm. The ECU can continually measure this current to determine if the fuel-air mix is correct and it can adjust the fuel flow through the injectors accordingly. On top of this, the ECU also looks at data coming from the oxygen (lambda) sensors in the exhaust. These tell the ECU how much oxygen is in the exhaust so it can automatically adjust for rich- or lean-running.

AIR CLEANER - Designed to trap the dust particles in the air that rush to the Carburetor. This function is performed by a replaceable cellulose filter element inside the Air Cleaner. It also acts as a flame arrester and an air silencer.

CARBURETOR - The section of the fuel system where gasoline is mixed with air to form an explosive vapor. Air enters at the top of a specially designed (Venturi) tube. The moving air-stream creates a suction at the Venturi which draws fuel into the air-stream from a fuel jet strategically located in the tube. The fuel coming from the Fuel Pump enters a float chamber where the level of the fuel is kept constant by a float. This float shuts a valve when the proper fuel level is reached. Since the proportions of the mixture of air and gasoline vary with the operating conditions of the engine, the amount of air admitted into the Carburetor must be controlled. This is achieved by the Choke Valve. When the Choke Valve is closed, very little air is admitted and the suction created by the Piston in its down stroke draws fuel from the jet. This mixture containing a large portion of fuel and a very small portion of air is called a rich mixture; such a mixture is required to start a cold engine. As the engine warms up, the extremely rich mixture must gradually be leaned until a steady air-fuel ratio of approximately 16 to 1 is reached.

- Float and Diaphragm Chambers

To make sure a carburetor has a good, constant supply of fuel to be sucked through the fuel jets, it has a float chamber or float bowl. This is a reservoir of petrol that is constantly topped up from the fuel tank. Petrol goes through an inline filter and a strainer to make sure it's clean of contaminants and is then deposited into the float chamber. A sealed plastic box is pivoted at one end and floats on top of the fuel. A simple lever connects to the float and controls a valve on the fuel intake line. As the fuel drops in the float chamber, the float drops with it which opens the valve and allows more fuel in. As the level goes up, the float goes up and the valve is restricted. This means that the level in the float chamber is kept constant no matter how much fuel the carburetor is demanding through the fuel jets. The quicker the level tries to drop, the more the intake valve is opened and the more petrol comes in to keep the fuel level up. This is why carburetors don't work too well when they're tipped over - the float chamber leaks or empties out resulting in a fuel spill - something you don't get with injectors. To combat this, another type of chamber is used where carburetors can't be guaranteed to be upright. These use diaphragm chambers instead. The principle is more or less the same though. The chamber is full of fuel and has a rubber diaphragm across the top of it with the other side exposed to ambient air pressure. As the fuel level drops in the chamber, the outside air pressure forces the diaphragm down. Because it's connected to an intake valve in the same way that the float is in a float chamber, as the diaphragm is sucked inwards, it opens the intake valve and more fuel is let in to replenish the chamber. Diaphragm chambers are normally spill-proof.

- Carb Icing

One of the problems with the spinning, compressing, vacuum-generating properties of the venturi is that it cools the air in the process. While this is good for the engine (colder air is denser and burns better in a fuel-air mix), in humid environments, especially cool, humid environments, it can result in carb icing. When this happens, water vapour in the air freezes as it cools and sticks to the inside of the venturi. This can result in the opening becoming restricted or cut off completely. When carburetors ice up, engines stop. In cars there is normally a heat shield over the exhaust manifold connected via a pipe to a temperature-controlled valve at the air filter. When its cold, the valve is open and the air filter draws warm air from over the exhaust manifold and feeds it into the carburetor. As the temperature warms up, the valve closes and the carburetor gets cooler air because the risk of icing has reduced. The symptoms of carb icing are pretty easy to diagnose. First, your engine bogs down at high throttle then it loses power and ultimately could stall completely. You'll stop on the side of the road and wait a couple of minutes, then the engine will start and run normally. This is because with the engine off, the heat from the engine starts to warm up the carbs and melts the ice so that when you try to start it up again, everything is fine.

The Ignition System consists of the spark plugs, coil, distributor, and battery, and provides the spark to ignite the air-fuel mixture in the cylinders of the engine. In order to jump the gap between the electrodes of the spark plugs, the 12-volt potential of the electrical system must be stepped up to about 20,000 volts.
The ignition system produces a high-voltage electrical charge and transmits it to the spark plugs via ignition wires. The charge first flows to a distributor, which you can easily find under the hood of most cars. The distributor has one wire going in the center and four, six, or eight wires (depending on the number of cylinders) coming out of it. These ignition wires send the charge to each spark plug. The engine is timed so that only one cylinder receives a spark from the distributor at a time. The generator is the basic source of energy for the various electrical devices of the automobile. An alternator that is belt-driven from the engine crankshaft is also used at times. To store excess output of the generator, a lead-acid battery is used which serves as a reservoir. Energy for the starting motor is thus made available along with power for operating other electric devices when the engine is not running or when the generator speed is not sufficiently high to carry the load. The starting motor then drives a small spur gear and meshes with gear teeth on the rim of the flywheel. As soon as the engine starts, the gear is disengaged, which prevents the starting motor from getting damaged. The starting motor is designed for high current consumption and delivers considerable power for its size for a limited time.

The Ignition System is designed to transform the low voltage form the Battery or Generator to the high tension voltage required to produce the sparks that ignite the compressed mixture of air and fuel in the combustion chambers.

IGNITION SWITCH - There are two separate circuits that go from the ignition switch to the coil. One circuit runs through a resistor in order to step down the voltage. The other circuit sends full battery voltage to the coil. Since the starter draws a considerable amount of current to crank the engine, additional voltage is needed to power the coil. So when the key is turned to the spring-loaded start position, full battery voltage is used. As soon as the engine is running, the driver releases the key to the run position which directs current through the primary resistor to the coil.

IGNITION COIL - The ignition coil is nothing more that an electrical transformer. A transformer designed to step up the 6 or 12 volts from the Battery and Generator to approximately 20,000 volts. The ignition coil is the heart of the ignition system. As current flows through the coil a strong magnetic field is built up. When the current is shut off, the collapse of this magnetic field to the secondary windings induces a high voltage which is released through the large center terminal. This voltage is then directed to the spark plugs through the distributor.

IGNITION WIRES - These cables are designed to handle 20,000 to more than 50,000 volts. The job of the spark plug wires is to get that enormous power to the spark plug without leaking out. Spark plug wires have to endure the heat of a running engine as well as the extreme changes in the weather. Spark plug wires go from the distributor cap to the spark plugs in a very specific order. This is called the "firing order" and is part of the engine design. Each spark plug must only fire at the end of the compression stroke. Each cylinder has a compression stroke at a different time, so it is important for the individual spark plug wire to be routed to the correct cylinder.

DISTRIBUTOR - Driven by the Camshaft, sends the high tension current it receives from the Ignition Coil to the proper Spark Plug at the correct instant the the corresponding piston reaches the top of the compression stroke. The high tension current enters the Distributor Cap at the center and passes to the Rotor. As the Rotor rotates within the Distributor Housing, it distributes the high tension current to each Cap Terminal in proper sequence or Firing Order.

SPARK PLUG - Consists of two electrodes. The central electrode is connected to a Cap Terminal of the Distributor. The side electrode is connected to ground. The gap between the electrodes causes the current to create a spark which explodes the mixture of air and fuel. The high voltage from your vehicle's high-tension electrical system is fed into the terminal at the top of the spark plug. It travels down through the core of the plug and arrives at the centre electrode at the bottom where it jumps to the ground electrode creating a spark. The insulator keeps the high-tension charge away from the cylinder head so that the spark plug doesn't ground before it gets a chance to generate the spark.

Ground electrode (ground strap) types. There are different types of grounding electrodes kicking around in spark plug designs nowadays, from 'Y' shaped electrodes to grooved electrodes like you'll find on Champion plugs all the way up to triple-electrode plugs like the high-end Bosch items. They're all designed to try to get a better spark, and to that end, you'll now find all sorts of exotic materials turning up too. Titanium plugs, for example, have better electrical conductivity than brass and steel plugs, and the theory is that they'll generate a stronger, more reliable spark.

Gapping a spark plug. Gapping a spark plug is the process of ensuring the gap between the two electrodes is correct for the type of engine the plug is going to be used in. Too large a gap and the spark will be weak. Too small and the spark might jump across the gap too early. Feeler gauges are used to measure the gap, and a gapping tool is used to bend the outer electrode so that the gap is correct.

Heat ranges. Something that is often overlooked in spark plugs is their heat rating or heat range. The term "heat range" refers to the relative temperature of the tip of the spark plug when its working. The hot and cold classifications often cause confusion because a 'hot' spark plug is normally used in a 'cold' engine and vice versa. The term refers to the thermal characteristics of the plug itself, specifically its ability to dissipate heat into the cooling system. A cold plug can get rid of heat very quickly and should be used in engines that run hot and lean. A hot plug takes longer to cool down and should be used in lower compression engines where heat needs to be retained to prevent combustion byproduct buildup.

Top Dead Center (TDC)

When a piston in an engine reaches the top of its travel, that point is known as Top Dead Center or TDC. The spark plug fires at this point. The electrical system in your car supplies voltage to your coil and ignition unit. The engine will have a trigger for each cylinder, be it a mechanical trigger (points), electronic module or crank trigger. At that point the engine sends a signal to the coil to discharge into the high voltage system. That charge travels into the distributor cap and is routed to the relevant spark plug where it is turned into a spark. The key to this, though, is the timing of the spark in relation to the position of the piston in the cylinder. Hence ignition timing. Having the spark ignite the fuel-air mixture too soon is basically the same as detonation and is bad for all the mechanical components of your engine. Having the spark come along too late will cause it to try to ignite the fuel-air mixture after the piston has already started to recede down the cylinder, which is inefficient and loses power.
Timing the spark nowadays is usually done with the engine management system. It measures airflow, ambient temperature, takes input from knock sensors and literally dozens of sensors all over the engine. It then has an ignition timing map built into its memory and it cross references the input from all the sensors to determine the precise time that it should fire the spark plug, based on the ignition timing map.

The lubrication system makes sure that every moving part in the engine gets oil so that it can move easily. The two main parts needing oil are the pistons (so they can slide easily in their cylinders) and any bearings that allow things like the crankshaft and camshafts to rotate freely. In most cars, oil is sucked out of the oil pan by the oil pump, run through the oil filter to remove any grit, and then squirted under high pressure onto bearings and the cylinder walls. The oil then trickles down into the sump, where it is collected again and the cycle repeats.

The Lubricating System is designed to apply lubricant to the moving parts of the engine in order to eliminate excessive friction which would otherwise rapidly wear them out. The lubricant not only reduces friction, but also reduces heat created by friction, prevents power leakage between piston and cylinders, and washes away particles or worn out metal.

ENGINE OIL - An engine oil's job is to stop all the metal surfaces in your engine from grinding together and tearing themselves apart from friction whilst transferring heat away from the combustion cycle. Engine oil must also be able to hold all the by-products of combustion in suspension. It cleans the engine of these chemicals and build-ups, and keeps the moving parts coated in oil. Finally, engine oil minimizes the exposure to oxygen and thus oxidation at higher temperatures. It does all of these things under tremendous heat and pressure.

Fully Synthetic	Characteristics
0W-30 0W-40 5W-40	Fuel economy savings Enhances engine performance and power Ensures engine is protected from wear and deposit build-up Ensures good cold starting and quick circulation in freezing temperatures Gets to moving parts of the engine quickly
Semi-synthetic	Characteristics
5W-30 10W-40 15W-40	Better protection Good protection within the first 10 minutes after starting out Roughly three times better at reducing engine wear Increased oil change intervals - don't need to change it quite so often
Mineral	Characteristics
10W-40 15W-40	Basic protection for a variety of engines Oil needs to be changed more often

-Viscosity is the single most important criteria of a lubricating oil. The basic performance of machinery is based on the viscosity of the lubricant. Viscosity is the resistance to the flowability of the oil. The thicker an oil, the higher its viscosity.

-Viscosity Index (VI) of a lubricant is an empirical formula that allows the change in viscosity in the presence of heat to be calculated. This tells the user how much the oil will thin when it is subjected to heat. The higher the viscosity index, the less an oil will thin at a specified temperature. Multi-viscosity motor oils will have a viscosity index well over 100, while single viscosity motor oils and most industrial oils will have a VI of about 100 or less.

OIL PUMP - Driven by the Camshaft, draws the oil from the Oil Pan through the screen of the Floating Oil Intake. This arrangement prevents any dirt, that may be deposited at the bottom of the Pan, from being drawn into the system.

OIL FILTER - Screens oil as it comes out of the Pump. A replaceable element traps dirt, carbon, sand and bits of metal. Clean oil is forced through the OIL GALLERIES, which are drilled in the Block, to each individual Camshaft Bearing and, from there, to each of the Main Bearings. The Crankshaft is drilled to permit oil to lubricate the Connecting Rods and the cylinder walls. Additional OIL GALLERIES bring lubricant to the Rocker Arm Shafts and, from there, to each Valve Rocker and Push Rod. Excess oil is then returned to the Oil Pan through drain holes and re-circulated throughout the engine.

CRANKSHAFT - A heavy steel forging shaft that carries offset portions known as Cranks which describe a circular motion when in operation. Between each pair of Cranks is a highly finished pin or Bearing Journal that carries the connecting rod bearing and piston assembly. As the piston and connecting rod assembly move in a vertical motion, the Crankshaft assembly converts this vertical motion to rotary or circular motion. It is this rotary motion that is delivered to the Flywheel and other driving components and eventually to the driving wheels. The Crankshaft is secured to the Crankcase by Main Bearing Caps which enclose additional highly finished pins known as the Main Bearing Journals.

FLYWHEEL - Mounted at the rear of the Crankshaft, its mass provides the inertia to carry the Pistons through the unproductive strokes of the cycle. In addition, it helps the engine to run smoothly.

VIBRATION DAMPER - Considered an additional Flywheel at the opposite end of the Crankshaft. It serves to dampen the vibrations of the engine resulting from torsion stresses.

CAMSHAFT - A straight shaft with a number of cams, accurately designed and precisely timed to lift each Valve at exactly the correct instant of the beginning of the intake and exhaust strokes, and to hold each Valve open for the correct length of time required to fulfill each cycle in each Cylinder. At the front is the Camshaft Gear which is twice the size of the one on the Crankshaft; thus for every two revolutions of the Crankshaft we have one revolution of the Camshaft.

CRANKCASE - The largest part of the engine. Together with the OIL PAN, at the bottom of the Case, it forms an oil tight housing in which all the rotating parts of the engine operate.

CYLINDER BLOCKS - Normally part of the Crankcase; they house the Cylinders, Pistons and Connecting Rods.

CYLINDER HEADS - Bolted to the Cylinder Blocks. Since the water must circulate from the Blocks to the Heads, a series of matching holes are provided in the Blocks and the Heads. The Heads house the Valves, their operating mechanisms and the Spark Plugs. To the Heads are bolted the Intake Manifold and the Exhaust Manifolds.

VALVES - They perform under unusually difficult conditions. They are exposed to the extremely high temperatures generated in the combustion chambers, temperatures which often reach the melting point of iron. They must be leak-proof even under the tremendous pressures of the explosions and open and close as often as 2,000 times every minute.

Spring-Return Valves - Spring return valves are about the most commonly-used and most basic type of valve train in engines today. Their operation is simplicity itself and there are only really three variations of the same style. The basic premise here is that the spinning camshaft operates the valves by pushing them open, and valve return springs force them closed. The cam lobes either operate directly on the top of the valve itself, or in some cases, on a rocker arm which pivots and pushes on the top of the valve. The three variations of this type of valve-train are based on the combination of rocker arms (or not) and the position of the camshaft.
The most basic type has the camshaft at the top of the engine with the cam lobes operating directly on the tops of the valves.
The second more complex type still has the camshaft at the top of the engine, but the cam lobes operate rocker arms, which in turn pivot and operate on the tops of the valves. With some of these designs, the rocker arm is pivoted in the middle and with other designed, it's pivoted at one end and the cam lobe operates on it at the midpoint.
The third type which you'll find in some motorcycle engines and many boxer engines are pushrod-activated valves. The camshaft is actually directly geared off the crank at the bottom of the engine and the cam lobes push on pushrods which run up the sides of the engine. The top of the pushrod then pushes on a rocker arm, which finally pivots and operates on the top of the valve.

Tappet Valves - Tappet valves area derivative of spring-return valves. The direct spring return valve described above would not act directly on the top of the valve itself, but rather on an oil-filled tappet. It's normally filled with oil through a small hole when the engine is pressurized. The purpose of tappets is two-fold. The oil in them helps quiet down the valve train noise, and the top of the tappet gives a more uniform surface for the cam lobe to work on. From a maintenance point of view, tappets are the items which wear and are a lot easier to swap out than entire valve assemblies.

The starting system is the heart of the electrical system in your car. The key is inserted into the ignition switch and then turned to the start position. A small amount of current then passes through the Neutral Safety Switch to a Starter Relay or Starter Solenoid which allows high current to flow through the Battery Cables to the Starter Motor. The starter motor then cranks the engine so that the pistons can create a suction that will draw a Fuel/Air mixture into the cylinder, where a spark created by the Ignition System will ignite this mixture.

Battery - The automotive battery is an electrochemical device that produces voltage and delivers current. The purpose of the battery is to supply current to the starter motor, provide current to the ignition system while cranking, to supply additional current when the demand is higher than the alternator can supply and to act as an electrical reservoir.

Battery Cables - Battery cables are large diameter, multi-strand wire which carry the high current necessary to operate the starter motor.

Ignition Switch - The ignition switch allows the driver to distribute electrical current to where it is needed. There are generally 4 key switch positions that are used:

Lock- The lock wafer tumblers or the lock sidebar are in the engaged (locked) position, which prevents the lock core (plug) from rotating.
Run- The vehicle has been electrically energized. Current is not supplied to the starter circuit.
Start- Power is supplied to the ignition circuit and the starter motor only. This position of the ignition switch is spring loaded so that the starter is not engaged while the engine is running.
Accessory- Power is supplied to all but the ignition and starter circuit.

Neutral Safety Switch - This switch prevents current to flow to the starter circuit when the transmission is in any gear but Neutral or Park on automatic transmissions. Standard transmission cars connect this switch to the clutch pedal so that the starter will not engage unless the clutch pedal is depressed.

Starter Relay - An automobile starter uses a large amount of current to start an engine. A starter relay is installed in series between the battery and the starter. Some cars use a starter solenoid to accomplish the same purpose of allowing a small amount of current from the ignition switch to control a high current flow from the battery to the starter.

Starter Motor - The starter motor is a powerful electric motor, with a small gear (pinion) attached to the end. When activated, the gear is meshed with a larger gear, which is attached to the engine. The starter motor then spins the engine over so that the piston can draw in a fuel/ air mixture.

IAUTOINFO.COM: AUTOMOTIVE CENTER

Automotive Information for the consumer