The lobe on the cam controlling the intake valve has moved out from under the valve lifter. Since the other valve is also closed, the upper end of the cylinder is sealed. Intake stroke. The intake FIG. Compression stroke. The valve to left has opened, and the intake valve has closed, and the piston is moving downward, drawing piston is moving upward, com- air and gasoline vapor into the pressing the mixture.
By the time the piston has moved up to TDC, the mixture will have been compressed to a seventh or an eighth of its original volume. That is like taking a gallon of air and compressing it to a pint. This results in a fairly high pressure in the cylinder.
Power Fig. The spark is produced by the ignition system discussed on a later page. It ignites, or sets fire to, the compressed air-gasoline-vapor mixture. Rapid com- bustion takes place; high temperatures and pressures result. At this instant, the resulting pressure on the top of the piston, pushing it down, may amount to as much as two tons on a piston 3 inches in diameter. Power stroke. The ignition FIG. Exhaust stroke.
The ex- system produces a spark that ignites haust valve to right has opened, the mixture. As it burns, high pres- and the piston is moving upward, sure is created which pushes the forcing the burned gases from the piston downward. Exhaust Fig. When the piston reaches BDC, the exhaust valve opens. Now, as the piston starts back up again pushed up by the rotating crankshaft , it forces the burned gases from the cylinder. By the time the piston has reached TDC, the cylinder is cleared of the burned gases.
The exhaust valve closes and the intake valve opens. Then, the piston starts back down again on the next intake stroke. A compression ring top and an oil-control ring bottom , with various parts named. External and sec- tional views of piston with four piston rings in place. The upper two, 1 and 2, are top and second compression rings. The lower two, 3, are oil- control rings.
Plymouth Divi- sion of Chrysler Corporation power strokes. To prevent the escape of much of this pressure past the piston between the piston and cylinder wall the piston must be equipped with rings. The reason is this: the piston can- not be machined accurately enough to provide a sealing fit with the cylinder wall. Furthermore, changes in di- mensions due to temperature changes might make it stick tight; this would mean that something might break rod, piston, crank- shaft. The metal of the piston expands with temperature increase; if the piston fit properly when cold, it would stick when hot.
To provide a good seal that will expand and contract with changing temperatures and also to compensate for cylinder-wall wear , piston rings are used. Typical piston rings are shown in Fig. The rings are of cast iron or similar metal. They have a joint which permits them to be expanded and slipped over the end of the piston.
There are grooves in the piston into which the rings are installed Fig. Actually, only the upper two rings shown in Fig. These rings, called the compression rings, do this by pressing tightly against the cylinder wall and also against the side of the ring groove in the piston. The lower two rings shown in Fig.
Their job is to scrape excessive amounts of lubricating oil off the cylinder walls. As we will mention again when we describe lubricating systems, considerable amounts of lubricating oil are thrown on the cylinder walls to provide for lubrication of the moving rings and piston.
In fact, there is so much oil that if most of it were not removed, it would work up into the combustion chamber and burn, producing carbon that would interfere with valve and spark-plug action so that engine performance would be very poor. The oil- control rings scrape off most of this oil from the cylinder walls and return it to the oil reservoir oil pan at the bottom of the engine. Multiple-cylinder engines You will remember that the cylinder produces only one power impulse every four piston strokes.
During exhaust, intake, and compression, the crankshaft is driving the piston, forcing it to push out the burned gases, to draw in a fresh charge, and to compress the charge. Thus, a one-cylinder engine would give power only one-fourth of the time and would not be smooth or powerful enough for automotive operation.
To prOVide for a more continuous flow of power, modern automotive engines use four, six or eight cylinders. With the six-cylinder engine, the power impulses would overlap to some extent while the eight- cylinder engine would have two power impulses going on at all times. This would give a relatively even flow of power. Engine flywheel Even though the power impulses of a multi- cylinder engine follow each other or overlap, additional smoothing out of the power impulses is desirable.
The engine flywheel does this job and thus improves the smoothness of the engine. Figure 1- 17 shows an engine crankshaft with the flywheel attached to one end. The flywheel is a relatively heavy metal wheel. It resists any sudden change of crankshaft or engine speed. Thus, when a power impulse starts with its initial high pressure , the crank- shaft is given a momentary hard push through the connecting rod and crankpin.
But the flywheel resists the tendency for the crank- shaft to surge ahead. Thus, the momentary power peaks are leveled off so that the engine runs smoothly. The flywheel also serves as part of the engine clutch on engines so equipped. In addition, the flywheel has teeth on its outer edge; the electric cranking-motor pinion teeth mesh with these teeth when the engine is being cranked for starting. Engine classifications Engines can be classmed in several ways.
They cla n be classified by the type of fuel they use [gasoline, LPG liquefred petroleum gas , or diesel fuel oil]. This is called a Fire Dome engine by the manufacturer; the combustion cham- bers are hemispherical in shape. Note valve and push-rod arrangement. Engines can also be classified as liquid-cooled or air-cooled, and this distinction is dis- cussed in the chapters on engine cooling systems.
Other ways of classifying engines are by number and arrangement of cylinders, and by arrangement of valves. These are discussed in the following sections. Valve arrangements for various engines. Cylinder arrangements Most automotive engines have four, six, or eight cylinders. All cylinders are similar in construction and in operation. Four-cylinder and Six-cylinder engines are in-line engines; that is, the cylinders are arranged in a Single row Fig.
Eight-cylinder engines may be in-line all cylinders in a single row or V In the V-8, the cylinders are arranged in two rows, or banks, which are usually perpendicular or 90 degrees to each other, Fig. An engine that has the valves in the . Valve-operating mechanism for an I-head, or overhead-valve, engine. Sectional view of an actual engine is shown in a. In b only the essential parts are shown, including the gears to drive the camshaft from the crankshaft, the valve lifters, push rods, rocker arms, and valves for one cylinder.
Com- parison of different types of valve and cylinder arrangement is shown in Fig. Figure shows the valve mechanism in an L-head engine. Figure shows the valve mechanism for an overhead-valve or I-head engine. In the L-head engine the valve lifter pushes up on the valve stem. Engine accessory system The engine requires four accessory systems to supply it with fuel and electric sparks, to cool it, and to lubricate it.
The fuel, lubricating, and cooling systems are con- sidered in detail in later pages in the book. The system that pro- vides the electric sparks the ignition system is discussed in detail in Automotive Electrical Equipment another book in the McGraw- Hill Automotive Mechanics Series. A brief discussion of the ignition system follows.
The ignition system The ignition system is part of the auto- motive electric system Fig. The electric system has several jobs to do. It cranks the engine for starting, supplies the electric sparks to ignite the compressed charges in the cylinders, operates the radio and car heater, supplies light for night driving, and operates gauges on the car dash that indicate battery charging rate, oil pressure, engine temperature, and level of fuel in the fuel tank.
Figure shows, in schematic view, a typical ignition system. It consists of the source of electric power the battery , ignition switch, ignition coil, ignition distributor, spark plugs, and wiring. The ignition has two jobs. First, it takes the low voltage from the battery or generator and steps it up to the several thousand volts needed to produce the sparks at the cylinder spark plugs. Secondly, it delivers each spark to the proper cylinder at the proper instant.
The voltage step-up job is done by the ignition coil and the distributor contact points. The contact points are mounted on a plate inside the distributor housing. One of the paints is stationary; the other is mounted on a movable arm.
This arm is moved by a breaker cam inside the housing. The breaker cam revolves it is driven by a gear from the engine camshaft , and as it does so, lobes on the cam cause the movable contact-point arm to move, closing and opening the contact pOints. When the contact paints are closed and ignition switch is on , electric current flows from the battery through the ignition coiL Then, a moment later, as the cam turns,further, a lobe on the cam moves the arm and separates the contact points.
The current stops flowing. Then, when the contact pOints separate and the current stops flowing, the electric energy is released from the coil in the form of a high-voltage surge. A typical one-wire automobile electric system. Return circuits between electric units are formed by the engine block and the car frame. The symbol -1 means ground, or return circuit.
United Motors Service Division of General Motors Corporation the contact pOints to prevent the high-voltage surge from discharg- ing across the contact points. This saves the surge for its designed purpose, which is to produce a spark at a spark-plug gap. The surge passes through the center terminal of the distributor cap. The center terminal is connected by a wire to the coil.
The center terminal is connected inside the cap by a contact spring to the distributor rotor. The rotor is mounted on the breaker cam so that it turns with the cam. Typical ignition system. It consists of the battery source of power , ignition switch, ignition coil, distributor shown in top view with cap removed and placed above it , spark plugs, and wiring. Units are not in proportion.
The outer terminals are connected by wires to the spark plugs in the engine cylinders. Thus, as each high-voltage surge is produced, it is led through the cap, rotor, and wiring to the spark plug of the cylinder that is ready to fire piston nearing TDC on the compression stroke.
But at higher speeds, the air-fuel mixture has less time to ignite and bum. Disassembled view of a distributor. Advance mechanism is to left. This means that the piston would be moving away from the pressure rise; much of the energy in the burning fuel would be wasted. Pressure will go up and more of the fuel energy will be used. Advance based on speed. To ignite the mixture earlier at high speed, a spark-advance mechanism is used. This mechanism is in- corporated in the ignition distributor.
One type consists of a centrifugal device that pushes the breaker cam ahead of the dis- tributor shaft as engine speed increases.
Figure shows the parts of this mechanism. The breaker cam is attached to an oval-shaped advance cam and this assembly sets down on a plate attached to the drive shaft. Centrifugal-advance mechanism showing initiaI- and maximum- advance positions. Figure also shows how the mechanism operates to move the breaker cam ahead as engine speed increases.
With increasing engine speed the advance weights move out against the weight-spring tension. This movement pushes the breaker cam ahead so that the cam lobes close and open the contacts earlier. The sparks thus occur earlier; the spark is advanced so that ignition occurs earlier in the com- pression stroke.
Different engines require different amounts of spark advance at various speeds. Typical advance curves are shown in Fig. In curve A, the spark is timed to occur just a few degrees of crank- shaft rotation before TDC during idle. Then, as engine speed is increased, tlle spark moves ahead, or advances, until it reaches a maximum of 28 degrees at 2, rpm revolutions per minute. It "dog-legs," or changes slope, at 1, rpm. A curve is worked out for each engine so that the advance at any particular speed will provide best performance.
The mechanism is then built to provide this advance. Figure illustrates a distributor that achieves spark advance with increasing speed by a different method. In this unit the con- tacts are mounted on a movable breaker plate.
The plate is linked to an airtight diaphragm. Typical centrifugal-advance curves. This movement causes the contacts to be closed and opened earlier so that a spark advance is produced.
The plate rotation results from the vacuum-line connection between the air- tight diaphragm on the distributor and an opening in the carburetor venturi. The greater the vacuum or the greater the engine speed , the further the diaphragm is moved and the more the plate mOves to advance the spark. Advance based on intake-manifold vacuum. Less air-fuel mixture gets into the engine cylinders and it is therefore less highly compressed.
This means the mixture burns more slowly. An additional spark advance, under these conditions, will allow the mixture ample time to burn and give up its energy to the piston.
Spark advance based on intake manifold vacuum is achieved by an airtight diaphragm linked to a movable breaker plate. This type of arrangement is shown in Fig. A vacuum connection is made to an opening just above the edge of the throttle plate B in Fig. Whenever the throttle is opened, its edge moves past the opening, thus introducing the intake manifold into the tube. This vacuum then causes diaphragm and breaker plate movement. The spark is advanced. Note that advance is based, in this arrangement, on manifold vacuum, which is part-throttle vacuum.
When the throttle is opened wide, there is no appreciable manifold vacuum and thus there will be no vacuum advance from this effect. Now that you have completed a chapter in the book, you will want to test your knowledge of the subjects covered in the book.
The questions that follow have two purposes. One is to test your knowledge. The second purpose is to help you review the chapter. The chances are that you will not be able to answer, offhand, all the questions. If this happens, turn back into the chapter and reread the pages that will give you the answer. Don't be discouraged if you can't answer all the questions. Most good students reread their lessons several times in order to be sure that the essential information will "stick" with them.
Rereading the pages and re- checking the questions will help you learn how to pick out and remember the important facts in the book. And it is these important facts that will help you when you go into the automotive shop, office, or laboratory. Correcting Parts Lists The purpose of this exercise is to give you practice in spotting unre- lated parts in a list.
For example, in the list, cylinder, piston, rings, whee'. In each of the lists, you will find one item that does not belong. Write down each list in your notebook, but do not write down the item that does not belong. The four piston strokes are intake, compression, injection, power, exhaust 2. The engine parts that change the reciprocating motion of the piston to rotary motion include the connecting rod, crank on crankshaft, cam on camshaft 3. The valve mechanism in the L-head engine includes the camshaft, valve spring, crankshaft, valve, spring retainer, lock 4.
The two types of piston rings are oil-control rings, compression rings, performance rings 5. The ignition system includes the ignition coil, ignition distributor, ignition switch, spark plugs, cranking motor, wiring Completing the Sentences The sentences below are incomplete. After each sentence thcre are sev- eral words or phrases, only one of which will correctly complete the sen- tence.
The connecting rod is attached to the piston by the rod cap piston pin cap bolts cap bearing 2. The connecting rod is attached to the crankpin on the crankshaft by the piston pin crank rod cap rod boots 3. In the standard engine each cylinder has one valve two valves three valves four valves 4. The two types of engine valves are intake and port intake and inlet intake and exhaust 5. The four strokes in the engine are, in order of occurrence, in- take, power, exhaust, and compression intake, exhaust, power and compression intake, compression, power, and exhaust 6.
During the power stroke, the intake and exhaust valves are, respec- tively, closed and opened opened and closed closed and closed 7. The device for smoothing out the power impulses from the engine is called the crankshaft camshaft flywheel clutch 8. The camshaft has a separate cam for each engine valve engine cylinder piston crankpin 9.
Also, you can inspect your own and your friends' cars as well as cars and engine components in the school automotive shop. You can go to a friendly automotive service shop where repair work on engines is done, By watching what goes on in the ordinary work of the day, you will learn much about these automotive components.
Perhaps you can borrow shop- repair manuals from your school automotive shop library or from the car-dealer service shop. Your school may have cutaway models of en- gines or other automotive parts. By studying all this material, you will better understand the construction and operation of the engine and thl' engine-accessory systems. This chapter de- scribes the fundamentals of the carburetor-type fuel system.
Chapter 6 discussed the fuel-injection system. Purpose of the fuel system The fuel system is designed to store liquid gasoline and to deliver it to the engine cylinders on the intake strokes in the form of vapor mixed with air.
The fuel system must vary the proportions of air and gasoline to meet the require- ments of different operating conditions. For example, during initial starting with a cold engine, the fuel system must deliver a very rich mixture rich in gasoline of about 9 pounds of air to 1 pound of gasoline.
Then, after the engine has warmed up, the mixture must be leaned out made less rich to about 15 pounds of air to 1 pound of gasoline. For acceleration or high-speed operation, the mixture must again be enriched. Components in the fuel system The fuel system Fig.
The accelerator pedal controls the amount of air-fuel mixture entering the engine cylinders, and thus the amount of power the engine produces. The fuel tank prOVides a reservoir, or storage space, for gasoline. The fuel gauge has an indicator needle on the car dash to indicate how full the fuel tank is. The fuel pump delivers gasoline from the fuel tank to the carburetor, and the carburetor mixes the gasoline with the air passing into the engine.
Fuel system in phantom view. Atoms and elements Before we go into detail on how the car- buretor and fuel system operate, let us talk about something that, at first, may seem unrelated to the subject.
We refer to atoms and elements. As we look around us, we can see thousands of different substances and materials, from wood to steel, from glass to cloth, from gasoline to water. Yet the amazing fact is that all these many substances are made out of only a few different types of "building blocks" called atoms.
Actually, there are about ninety different kinds of atoms. Each has a special structure that makes it different from other atoms, and each has a special name such as iron, copper, hydrogen, sulfur, tin, oxygen, and so on. A piece of iron, for example, is made up entirely of one particular variety of atom. A quantity of the gas oxygen is made up of a great number of another type of atom.
Any substance made up entirely of only one type of atom is called an element. The table on page 30 lists a number of the more com- mon elements. The ninety some kinds of atoms can combine in many ways to form hundreds of thousands of different combinations, or com- pounds.
We can compare this to the 26 letters of the alphabet, which can be combined in many ways to form the thousands of words in our language. Thus, salt, water, wood, glass, gasoline, the very blood and bones in our bodies are made up of compounds produced by the combining of a few types of atoms. Salt is made up of atoms of the elements sodium and chlorine.
Water is made up of atoms of the elements of hydrogen and oxygen. Size of atoms Individual atoms are far too small to see. There are billions upon billions of atoms in a single drop of water. To give you an idea of how small atoms really are, suppose we could expand this cubic inch until it was large enough to contain the earth.
That means each edge would measure 8,OQO miles instead of an inch. If the atoms were ex- panded in proportion, each atom would then measure about 10 inches in diallleter. Atomic structure All of us, in this atom-bomb age where "splitting the atom" is commonplace, have heard something of the atom. We have mentioned that there are more than ninety varieties of atoms. But basically, all atoms are composed of no more than three fundamental particles called electrons, protons, and neutrons.
For instance, the hydrogen atom is made up of a proton at its center or nucleus and an electron circling the proton at high speed Fig. The electron has a charge of negative electricity in- dicated by a - sign.
There is a strong attraction between positive and negative charges; this attraction tries to pull the electron into the nucleus. But balancing this pull is the tendency that the electron has to flyaway from the nucleus due to its rotary motion that is, FIG.
This is the same balancing of forces you get when you whirl a ball on a rubber band around your hand Fig. The rotary motion or centrifugal force tends to move the ball away from your hand, but the rubber band or attractive force keeps the ball moving in a circle around your hand.
The helium atom helium, like hydrogen, is a gas has 2 protons in its nucleus and 2 electrons circling the nucleus. In addition, it has 2 neutrons in its nucleus Fig. The apparent function of the 2 neutrons is to hold the two protons together, though how they do this is not known. But if the neutrons were absent, the protons would fly apart, and there would be no helium atom. The reason the two protons would fly apart is that their positive charges repel each other, if the neutrons are not present.
The neutrons are neutral electrically; they have nO electric charge. Lithium a light metal , for example, has 3 protons, 4 neutrons, and 3 electrons. Next comes beryllium another light metal with 4 protons, 5 neutrons, and 4 electrons; boron with 5 protons, 5 neutrons, and 5 electrons; carbon with 6,6, and 6; nitrogen with 7,7, and 7; oxygen with 8,8, and 8. Note that each atom normally has the same number of electrons as protons.
This makes the atom electrically neutral since there is a negative elec- trical charge or electron for every positive charge or proton. Molecules We have already mentioned that the many sub- stances, or compounds, in the world are made up of different combinations of atoms. The electron in a hydrogen atom FIG.
A helium atom. This is like combining letters to form words. For example, when two atoms of hydrogen and one atom of oxygen are combined, a molecule of water is formed. When an atom of carbon is combined with two atoms of oxygen, a molecule of carbon dioxide is formed. Refresh and try again. Crouse ,. Donald L. Donald Anglin. William Harry Crouse ,. To add more books, click here.
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