and Operation of Engine Fundamentals 5 - g w · PDF fileChapter 5 Fundamentals of Engine Construction and Operation 75 Pistons and Rings Pistons transfer the force of expanding combustion

Balance shaftsCamshaftCamshaft drive

mechanismCompression strokeConnecting rodsCoolant passagesCoolant pump

Coolant-recoverysystem

Cooling systemCrankshaftCylinder headEngine blockEngine coolantEngine oil

Exhaust strokeExhaust valvesIntake strokeIntake valvesLiftersLubrication systemOil filterOil galleries

Oil panOil pickup screenOil pumpPistonsPower strokePressure regulatorPush rodsRadiator

Radiator fanRadiator pressure capRocker armsSerpentine beltThermostatValve timingValve train Variable valve timingVibration damper

Know These Terms

73

Fundamentals of Engine Constructionand Operation

Chapter 5

After studying this chapter, you will be able to:Describe each stroke of a four-stroke cycle engine.Identify and explain the purposes of the major components of the engine compression system.Explain the operating principles of liquid cooling systems.Identify cooling system parts.Explain the engine lubricating system.Identify lubrication system parts.List common oil classification systems.

This sample chapter is for review purposes only. Copyright © The Goodheart-Willcox Co., Inc. All rights reserved.

74 Auto Engine Performance and Driveability

Engine problems can have a major effect on vehicle driveability. For example, without good compression or proper valve timing, the engine will not properly operate. This chapter covers the major engine components and reviews engine operation.

Four-Stroke Cycle Engine Operation

One power cycle in an automotive engine is a four-stroke process, which is why these engines are known as four-stroke cycle engines. The piston moves up twice in the cylinder and down twice in the cylinder for each power-producing cycle. This requires two revolutions of the crankshaft. Refer to Figure 5-1 as you read the following paragraphs. Some diesel engines, however, use only two strokes rather than four.

The downward movement of the piston on the intakestroke draws the air-fuel mixture into the cylinder through the intake valve(s). When the piston reaches the bottom of the intake stroke, the intake valves are closed. The piston then moves up in the cylinder, compressing the air-fuel mixture. This is called the compression stroke. When the air-fuel mixture in the cylinder is ignited, the burning fuel and oxygen produce heat. The heat causes the gases in the cylinder to expand, forcing the piston down under pres-sure. This is called the power stroke.

The downward motion of the piston is transferred to the connecting rod, which in turn pushes on the crankshaft. The connecting rod and crankshaft arrangement changes the linear piston movement into rotation of the crankshaft. This rotational movement is used to move the vehicle.

When the piston reaches the bottom of the power stroke, the exhaust valve is open. The exhaust stroke then begins as the piston moves up the cylinder, pushing the exhaust gases out of the open exhaust valve. One cycle is now complete. The cycle then repeats.

Engine Components

This section describes the major components of the engine compression system. The compression system con-tains the parts that develop engine compression and allow the heat energy in the burning air-fuel mixture to become mechanical energy.

Engine block.Pistons.Rings.Connecting rods.Crankshaft.Cylinder heads.Valves and related components.Valve train.Harmonic balancers.Balance shafts.

Although the exact design and number of engine compo-nents varies with the type of engine and number of cyl-inders, the basic components and their functions are the same as described here.

Engine BlockThe engine block is the basic support and attaching

point for all other engine parts. Engine blocks are made by pouring molten cast iron, steel, or aluminum into molds, Figure 5-2A. After the metal cools, the molding sand is washed out and the block is machined to allow other parts to be installed or attached, Figure 5-2B. The major parts installed in or on the block are the pistons, crankshaft, cam-shaft, cylinder heads, and manifolds.

Figure 5-1. The cycle shown here is typical of all four-stroke cycle engines: intake, compression, power, and exhaust.

Intake

Compression

Power

Exhaust

31

2 4

Chapter 5 Fundamentals of Engine Construction and Operation 75

Pistons and RingsPistons transfer the force of expanding combustion

gases to the connecting rods. They are made of aluminum to reduce weight. Most automotive pistons have two com-pression rings and one oil ring, as shown in Figure 5-3.

Compression rings seal in the pressure created dur-ing the compression and power strokes. If this pressure is allowed to leak out, the engine will not start or will have severe power and driveability problems. The compres-sion rings are installed at the top of the piston. A film of oil between the compression ring and cylinder wall seals pressure in the cylinder. This oil film is only about .001(.0025 mm) thick, but if it is removed, the engine will not develop enough compression to start.

The oil-control ring is installed below the compres-sion rings to prevent excessive oil consumption. During the piston’s intake stroke, vacuum in the cylinder tries to pull oil from the cylinder wall. To reduce oil loss, the oil-control ring scrapes most of the oil from the cylinder wall when the piston is moving down in the cylinder. A small amount of oil passes by the oil-control ring to seal the compression rings against the cylinder wall.

Connecting Rods and CrankshaftThe connecting rods are forged steel rods that connect

the piston to the crankshaft. They transfer the force from the piston to the crankshaft. Each connecting rod is connected to a piston by a piston pin. The rod is attached to the crank-

Figure 5-2. A—The engine block starts out as molten metal poured into a mold. B—The casting is then machined to accept and support the other engine parts. (BMW, Honda)

A B

Figure 5-3. The pistons and rings are the parts that most people associate with the compression system. A—This shows the various parts of the piston. B—Compression and oil-control ring installation. Most engines with spark ignition use this type of ring configuration.

Head

Skirt

Ringgrooves

Oil-controlring

Compressionrings

{

A B


shaft by a bearing cap and bearing inserts that surround the crankshaft journal. The piston pin and crankshaft bearings allow the rod to move in relation to both the piston and crankshaft. Refer to Figure 5-4.

The crankshaft converts the straight-line force from the piston and connecting rod into rotary force. It is attached to the engine block by bearing caps and bearings that sur-round the crankshaft journal, Figure 5-5. This design allows the crankshaft to rotate inside of the bearings with minimal friction. The bearing caps are held to the engine block by two, four, or six bolts torqued to specifications.

Cylinder HeadsThe cylinder head contains the combustion chamber

for each cylinder and forms the top of the cylinder. Cylinder heads contain the intake and exhaust valves and, in some cases, the camshaft and lifters. They also contain oil gal-leries, coolant passages, and openings to allow the flow of intake and exhaust gases. Cylinder heads are made from either cast iron or aluminum. A sheet metal, cast aluminum, or plastic valve cover is installed over the upper valve train components. Figure 5-6 shows a typical cylinder head.

Coolant passages between the cylinder heads and engine block must be sealed to prevent coolant leakage. Also, the pressure of expanding combustion gases must be contained within the cylinder. Head gaskets are used between the head and engine block for these purposes. They are thin and made from steel, copper, and fibers.

The cylinder head and head gasket are secured to the block with head bolts. These must be torqued to specifica-tions. A few engines have studs and nuts, rather than head bolts. Valves and Related Components

One or more intake valves are used to control the flow of the air into each cylinder. One or more exhaust valvesare used to control the flow of exhaust gases out of each cylinder. Valves also seal the cylinder during the com-pression and power strokes. They are occasionally called mushroom valves due to their resemblance to a mushroom. Intake and exhaust valves are identical in shape, but intake valves are usually larger. Opening and closing of the valves are controlled by the valve train.

The valve spring holds the valve against its seat, keep-ing it closed. Valve springs are always slightly compressed when installed. This ensures that the valve closes tightly. The spring is held to the valve by valve spring retainers. The retainer is a cap which covers the spring. A locking device, usually called a split keeper, locks the cap to the valve stem. A valve and spring assembly is shown in Figure 5-7. The assembly is held together by the pressure of valve spring acting against the cylinder head.

The valve stem slides up and down in a valve guide. The guide may be integral to the cylinder head or a remov-able insert. It keeps the valve steady and provides a smooth surface on which the stem can slide. The oil seal at the top of each valve stem prevents engine oil from entering the combustion chamber. Without a seal, oil would be pulled

Figure 5-5. The crankshaft is the engine part that converts the piston’s up-and-down (reciprocating) motion into rotary motion. It delivers power to the drive train. (Ford)

Make sure the tabon the bearingfits tightly intothe matching

notch in the cap

Make sure the tabon the bearingfits tightly intothe matching

notch in the block

Thrust bearings

Main bearing

caps

Bearing inserts(lower)

Bearing inserts(upper)

Crankshaft

Figure 5-4. The connecting rods attach the pistons to the crankshaft. (Ford)

Piston

Bolt

Nut

Connectingrod

Bearinginserts

PistonPin


from the cylinder head, between the valve stem and guide, and into the combustion chamber. The valve seal may be an umbrella type or an O-ring installed between the valve stem and valve retainer.

When the valve is in contact with its seat, heat is transferred from the valve to the cylinder head. This trans-fer is most critical for exhaust valves, since they absorb more heat of combustion. If the heat is not transferred to the head, the valve may melt. Some valves are filled with metallic sodium to further aid in heat transfer. The intake valves are cooled by the incoming air and are not as prone to damage.

The valve-to-seat contact is controlled by the valve clearance. Valve clearance is the amount of loose-ness in the valve train between the camshaft and valve stem. Valve clearance can sometimes be adjusted. Valve clearance has more effect on valve life than on engine performance.

Valve TrainThe valve train is the group of components that control

the opening and closing of the valves. Valve train opera-tion is similar in both overhead camshaft and cam-in-block engines. The engine crankshaft turns camshaft via a chain, belt, or gear set. The camshaft controls the distance the valves open and the duration of time over which they are open. There is one camshaft lobe for each valve.

In a cam-in-block engine, the camshaft lobes push on valve lifters installed into bores machined into the block. The motion is transferred through push rods and rocker arms to the valves. The valve spring pressure is overcome and the valves are forced open. The valve remains open

Figure 5-6. The cylinder head contains the valves and acts as a cap on the top of the engine. Along with the cylinders, it forms combustion chambers for each cylinder. (BMW)

Spark plug

Combustionchamber Exhaust

valves

Coolant passages Intake valves

Figure 5-7. The valve assembly consists of the valve, valve spring, retainers, stem lock, and oil seals. (Ford)

Split Keeper

Valve stem seal

Valve

Sleeve

Spring

Retainer


until the camshaft lobe allows the valve spring to reseat the valve. On overhead camshaft engines, the cam lobes usually push directly on the valve rocker arm, Figure 5-8.There are no push rods.

Valve TimingThe valves must open and close in proper relation to

the movement of the piston or the engine will not run. This relationship is called valve timing, not to be confused with ignition timing. Valve timing is determined by the relative positions of the crankshaft and camshaft. The intake valve must also open wide enough and long enough to allow the air-fuel mixture to get into the cylinder. The exhaust valve must do the same to allow the exhaust gases to get out of the cylinder.

Lift is how wide the valve opens. Duration is the amount of time that the valve stays open. Overlap is the amount of time that both intake and exhaust valves are open. Lift and duration are determined by the shape of the camshaft lobes. Valve timing, lift, and duration have a big effect on engine driveability.

The crankshaft always turns two complete revolutions for every one revolution of the camshaft. This is because any cylinder in a four-stroke cycle engine, whether gasoline or diesel, requires two complete revolutions of the crankshaft to complete all four cycles. However, each valve in the engine opens only once during all four strokes. To accom-plish this, the driving gear on the crankshaft always has half the number of teeth as the driven gear on the camshaft.

Valve LiftersValve lifters transmit the motion of the camshaft lobes

to the push rods or rocker arms. Lifters can be mechanical or hydraulic. Mechanical, or solid lifters, must be periodi-cally adjusted. Hydraulic lifters are self adjusting.

A typical hydraulic lifter is shown in Figure 5-9. The outer lifter body contacts the camshaft lobe. The inner piston (plunger) contacts the push rod or rocker arm. The space between the lifter body and the plunger is filled with engine oil. This oil is supplied by the lubrication system through a small passage.

When the camshaft lobe pushes the lifter body upward, the oil passage into the lifter is sealed off. Since the oil can-not escape or compress, the hydraulic lifter acts as a solid unit and opens the valve. When the cam lobe allows the lifter to move down, the lifter oil passage is again open and oil can flow into the lifter. Engine oil pressure pushes the plunger upward to remove any valve train clearance, but does not have enough force to open the valve.

The friction between the lobes and lifters is the highest friction in the engine and can cause the camshaft and lifters to rapidly wear out. To reduce friction, the camshaft lobes are tapered and the lifters offset. This causes the lifters to rotate as they are pushed up by the lobe. This rolling action between the lobe and lifter helps the lobes to evenly wear. To further reduce friction, many late model engines use roller lifters. A roller is installed on the bottom of the lifter and turns with the lobe as the camshaft rotates.

Push Rods and Rocker ArmsPush rods are used only on cam-in-block engines.

They transmit the lifter motion to the rocker arm. Many push rods are hollow. Oil from the lifter flows through them to lubricate the rest of the valve train. Rocker arms are piv-oting levers that convert the upward movement of the push rod or lifter into downward movement of the valve.

Figure 5-8. The overhead camshaft valve train allows quicker valve response with less play and friction between the com-ponents. Overhead camshafts are either belt or chain driven. (Subaru)

Spring

Oil hole

Plunger

Plungerspring

Check ballretainer

Checkball

Body

Valverocker

Lashadjuster

Figure 5-9. Hydraulic lifters use the engine oil pressure to auto-matically eliminate play from the valve train. Hydraulic lifters are used on almost all cam-in-block engines. (Ford)

Push rod cup

Check valve

Body

Plunger

Lockring

Check valveretainer

Check valve spring

Plunger spring

Metering valve disk


On overhead cam engines, the camshaft is installed on top of the cylinder head. It opens the valves from above. In some overhead cam engines, the lifter is placed between the cam lobe and the rocker arm. In many cases, the rocker arm is directly operated by the camshaft. A hydraulic lash adjuster, similar in operation to a hydraulic lifter, maintains the proper valve clearance. See Figure 5-10.

Camshaft Drive MechanismsTo maintain the relationship between the valves and

pistons, one of three types of camshaft drive mechanismsis used. In all cases, the gear or sprocket on the crankshaft has exactly half the number of teeth on the camshaft gear or sprocket. This causes the camshaft to turn at exactly half of the crankshaft speed.

A few vehicles use a gear drive, Figure 5-11. This type of drive has two meshing gears. The crankshaft gear rotates to drive the camshaft gear.

The majority of overhead valve, cam-in-block engines use a chain drive, Figure 5-12. The crankshaft gear drives the chain. The chain then drives the camshaft gear.

A few overhead camshaft engines use a chain drive. However, most overhead camshaft engines use a belt drive, Figure 5-13. In this design, the belt is driven by a crankshaft sprocket. The belt then drives the camshaft sprocket. On these designs, the belt often drives the water pump and oil pump. Some overhead camshaft engines use a system that is a combination of chain and belt drives.

Variable Valve Timing DevicesIn the past, the valve timing set by the relationship

of the drive and driven sprockets or gears could not be changed once the engine was assembled. An increasing

Figure 5-10. Lash adjusters are used in the valve train for an overhead camshaft engine. They use the same principle as the hydraulic lifter, but are installed on the rocker arm or on the opposite side of the valve stem. (Ford)

Hydrauliclash adjuster

Rollerfollower

Valvestem

Cam

Figure 5-11. A few spark-ignition engines use gears as the cam-shaft drive mechanism. Gear drive is more common in diesel engines.

Camshaftgear

Crankshaftgear

Timing marks

Figure 5-12. Chain camshaft drive mechanisms are most com-mon on cam-in-block engines. However, some overhead cam-shaft engines also have chain camshaft drives. Note the timing marks on both the camshaft and crankshaft timing gears.

Camshaftgear

Crankshaftgear

TimingmarksChain


number of engines have some form of variable valve timing. Variable valve timing allows the timing of the valve opening and closing to be varied based on driving conditions. Two general types of variable valve timing are used on engines:

Camshaft timing adjustment. These adjusters are mounted on the end of the camshaft where it is fas-tened to the driven sprocket or gear.Camshaft lift and duration adjustment. These adjusters are mounted at the camshaft lobes and rocker arms.

The vehicle computer operates the adjusters based on sen-sor inputs. The types of variable valve timing devices are discussed in more detail in Chapter 10.

Vibration DamperWhen the engine cylinders fire, force is transmitted

to the crankshaft. When it receives this force, part of the crankshaft tends to rotate before the rest of the crankshaft. This causes a twisting of the crankshaft. When the force is removed, the partially twisted shaft unwinds. This unwind-ing action, although minute, causes what is known as tor-sional vibration. To stop the vibration, a vibration damper,sometimes called a harmonic balancer, is attached to the front of the crankshaft. It consists of two heavy rings con-nected by rubber plugs, spring-loaded friction discs, or a combination of the two.

When a cylinder fires and the crankshaft speeds up, the outer ring of the damper has a tendency not to rotate. As a result, the rubber connecting the two rings of the damper flexes. As the crankshaft tries to unwind after the cylinder has fired, the outer ring of the damper again tends not to rotate in the opposite direction and the rubber flexes. The unwinding force of the crankshaft is cancelled out by the damper. On some newer engines, the crankshaft pulley is an integral part of the balancer.

The engine flywheel also absorbs vibration. The flywheel used with manual transmissions is heavy and absorbs vibration. Automatic transmission flywheels are lightweight steel stampings. The torque converter absorbs most of the vibration.

Balance ShaftsIn some engines, one or more balance shafts are

added to counterbalance vertical and torsional vibrations. A balance shaft has offset weights that rotate in the opposite direction of the crankshaft. These shafts are either turned by the camshaft through direct gearing or by the crankshaft through a belt or chain. Balance shafts help to provide a smoother idle and less vibration from the engine.

Engine-Related Systems That Can Affect Driveability

The following sections cover systems related to the engine that can affect driveability. These systems are all part of the overall basic engine and affect engine operation if they are not properly operating.

Cooling SystemThe cooling system is a set of components that remove

unwanted engine heat and regulate engine temperature. A cooling system is needed because not all of the heat of combustion creates pressure to move the pistons. The excess heat must be removed to prevent engine damage. Even a slightly overheating engine experiences excess wear

Figure 5-13. Belt camshaft drive mechanisms are used on overhead camshaft engines. Some dual overhead camshaft engines use a combination belt and chain system to drive the camshafts.

Camshaftsprocket

Stationarymark

Timing mark

Stationary mark

Timing mark

Crankshaftsprocket

Belt

Tensioner


due to the tighter-than-normal clearances between moving parts. An excessively hot engine tends to ping, diesel, or be hard to start. It may also be hot enough to melt the exhaust valves. This is usually called valve burning.

Some of the engine heat is removed by the exhaust gases and some radiates out of the engine block and heads. The rest of the heat must be removed by the cooling system. The amount of heat removed must be controlled so that the engine does not run cooler than its normal operating tem-perature. An engine that runs too cold wastes fuel, drives poorly, pollutes the air, and quickly wears out.

All cooling systems remove excess heat from the engine and transfer it to the surrounding air. The two main kinds of cooling systems are liquid cooling and direct air cooling. In liquid cooling, the heat is absorbed by a liquid, which then transfers it to the air. In direct air cooling, the heat is directly transferred to the air.

Liquid CoolingAll cars and light trucks manufactured today have a

liquid cooling system. The engine block and cylinder head has many internal passages through which coolant circu-lates. The coolant is moved through the cooling system by a pump. As the coolant circulates through the passages, it picks up heat from the surrounding metal. The coolant then flows from the engine into the radiator. As the cool-ant travels through the radiator, heat is transferred from the coolant to the air passing through the radiator. A fan draws air through the radiator at low speeds. At higher speeds, the movement of the vehicle forces air through the radia-tor. The cooled liquid then returns to the engine to pick up more heat. Figure 5-14 shows a typical cooling system.

Engine Coolant. The engine coolant is the medium of heat transfer. It must be able to absorb and release heat without damaging any cooling system parts. Engine coolant

Figure 5-14. Components of a typical cooling system. As coolant circulates through the engine, it picks up heat. This heat is trans-ferred to the air by the radiator.

Lower (return)radiator hose Engine oil

cooler lines Coolant pump

Oil filter

Heater hoses

In-tank heat exchanger

In-tank heat exchanger

Fan and motor

RadiatorHeater core

Coolant first flows through the heads and then block

Transaxle fluid cooler lines

Thermostathousing

Upper radiator hose


is a mixture of antifreeze and water. There are many types of antifreeze. Some contain ethylene glycol or propylene glycol. Also included are corrosion inhibitors to reduce rust and corrosion of the engine block and radiator. Small amounts of water-soluble oils are added to lubricate seals and moving parts. Some antifreeze solutions use organic acid technology (OAT) to lengthen the life of the coolant.

Pure ethylene glycol freezes at about 9 F (–13 C) and water freezes at 32 F (0 C). When ethylene glycol and water are mixed, however, the freezing point of the mix-ture is lower than either liquid alone. A 50:50 mixture of ethylene glycol and water freezes at about –35 F (–37 C).A mixture of 2/3 ethylene glycol and 1/3 water freezes at about –67 F (–55 C). A 50:50 mixture of propylene glycol and water freezes at about –26 F (–32 C). Most engine manufacturers recommend a 50:50 mix of either ethylene glycol or propylene glycol antifreeze and water.

A mixture of antifreeze and water has a higher boil-ing point than plain water. A 50:50 mixture boils at about 222 F (106 C). This gives added boil-over protection for summer driving. Up to a 70:30 mixture of antifreeze and water is sometimes used in severe climates and operating conditions.

Antifreeze is colored with dyes. Color does not deter-mine whether a particular antifreeze is suitable for a par-ticular engine. Consult the service information for a vehicle to determine which antifreeze to use.

Warning: Most antifreeze is poisonous to humans and animals. Ingesting a very small amount of antifreeze can lead to kidney

failure and death.

Coolant Pump. The coolant pump, or water pump, consists of a cast iron or aluminum housing contain-ing an impeller. The impeller is constructed with blades, Figure 5-15. As the impeller rotates, coolant is thrown to the outside of the impeller. This type of pump is known as a centrifugal pump. It is capable of circulating several hun-dred gallons of coolant per hour at about 1 psi or 2 psi.

The pump intake is connected by a flexible hose to the bottom of the vehicle radiator. Coolant is drawn into the center of the rotating pump by suction. The coolant is thrown outward by centrifugal force. Passages in the pump and engine direct the coolant through the block and heads.

Coolant Passages. Internal coolant passages, or water jackets, are cast into the block and heads during manufac-ture. Coolant is pushed through the coolant passages by the coolant pump. The coolant absorbs heat before exiting through the top of the engine. Passages near the hottest parts of the engine, such as near the valves and cylinder walls, are designed so that more coolant flows through them. Some internal coolant passages have external holes for manufacturing purposes. These are sealed with metal plugs called core plugs, or freeze plugs, Figure 5-16. Core plugs may be pressed in or threaded.

Radiator. The radiator is a heat exchanger consisting of tubes and fins. As the coolant flows through the tubes, heat is transferred to the fins. The fins then transfer the heat to the air passing through the radiator. In most vehicles, the radiator is capable of removing more heat than the engine can produce. Actual radiator efficiency depends on the flow rate of the coolant and the outside air temperature.

Most radiators are cross-flow radiators. In this design, coolant flows from one side of the radiator to the other. Tanks on the left and right sides of the radiator direct cool-ant into the radiator tubes or to an outlet that leads back to the engine.

Radiators used on cars with automatic transmissions/transaxles have a heat exchanger mounted in the radiator to cool the transmission fluid. Hydraulic pressure in the transmission/transaxle forces the fluid through the heat exchanger. The fluid, which is at a higher temperature than the coolant, gives up heat to the engine coolant. The trans-mission cooler is always mounted in the radiator tank that feeds coolant back into the engine.

Radiator Fan. The radiator fan draws extra air through the radiator to aid in heat transfer at low speeds. Most fans are electric. See Figure 5-17. The fan is controlled by either thermostatic switches installed in a passage of the cooling system or through the engine control computer. The fan remains off until the coolant temperature reaches a certain point. The fan will continue to run after the engine

Figure 5-15. The coolant pump uses an impeller to move the coolant through the engine. Coolant pumps are either belt- or gear-driven.

Drive pulley Housing

Inlet(lower radiator

hose connection)Impeller

Coolant isthrown

outwardby the impeller


is shut off until the coolant temperature falls to a certain point. In addition, the fan is turned on any time the air conditioner compressor is operating, no matter what the coolant temperature.

Some longitudinal engines have belt-driven fans. These fans are usually installed on the end of the coolant pump shaft so that the same pulley drives the pump and the fan. Many belt-driven fans have a fluid clutch installed between the drive pulley and fan assembly, Figure 5-18.

The fluid clutch allows the fan to freewheel, or not be driven, at higher speeds when it is no longer needed. Some fluid-clutch fans contain a thermostat that prevents the fan from operating until the engine warms up. Other fluid-clutch fans contain a flow-control solenoid. The solenoid is operated by the vehicle computer based on temperature sensor inputs.

Radiator Pressure Cap. The radiator pressure capis a valve that allows pressure to build up in the cooling system. See Figure 5-19. It does so by using spring pressure to hold a seal against the radiator filler neck. The spring is calibrated to produce the proper system pressure. As the engine heats up, coolant pressure builds until it overcomes spring pressure and opens the valve. When the excess pres-sure is released, the spring closes the valve.

Figure 5-16. Core plugs are installed in various locations in the front, sides, and rear of the block. The holes sealed by these plugs are used to remove molding sand after the block is cast. (Ford)

Typical coreplug locations

Figure 5-17. One or more electric fans are used on all front-wheel and many rear-wheel drive vehicles. The electric fan allows for better control of fan operation as well as more avail-able horsepower from the engine. (Chrysler)

Crossflowradiator

Air-temperature-sensingswitch

Radiator fanswitch

Electricfan motor

Fanshroud

Enlargedview—note polarity

Automatictransmission

oil coolerfittings

Figure 5-18. Some vehicles have belt-driven fans. The fan clutch allows the fan to freewheel at highway speed. This reduces the load on the engine.

Fan clutch

Fanblades

Serpentine belt

Coolantpump

Drivepulley

Figure 5-19. Radiator pressure caps are not a frequent source of driveability or engine problems; however, a faulty cap can cause diminished overheating protection. Never open a radiator pressure cap when the cooling system is under pressure.


The cooling system is pressurized to raise the boiling point of the coolant. The boiling point of any liquid goes up as the pressure is increased. For every 1 psi (6.9 kPa) increase in pressure, the coolant boiling point increases by 3 F (1.7 C). Therefore, a 15 psi (105 kPa) pressure cap will raise the boiling point of the coolant by 45 F (25.5 C).

Coolant-Recovery System. The coolant-recoverysystem is designed to keep the cooling system as full as possible at all times. The system consists of a tank con-nected by a hose to the radiator overflow neck, as shown in Figure 5-20. The plastic tank is called the recovery tank. Coolant that is pushed out of the radiator as the engine heats up enters the recovery tank. When the cooling system loses heat, a lower pressure is created in the radiator. The difference between this pressure and atmospheric pressure draws coolant from the recovery tank into the radiator.

Warning: Some coolant-recovery systems are pressurized. The cap on the recovery tank is a pressure cap like the one found on

the radiator. Never open a pressurized recovery tank if the cooling system is under pressure.

Thermostat. The thermostat helps the engine to quickly warm up by keeping coolant from circulating through the radiator when the engine is cold. The thermostat is located at the engine outlet gooseneck. This is where coolant leaves the engine on its way to the radiator.

The thermostat consists of a heat-sensitive material, such as wax, sealed in a chamber with a piston at one end. The piston is attached to a valve that opens or closes the thermostat to control coolant flow, Figure 5-21.

When the coolant is cold, the wax is contracted and holds the piston in the closed position. As the coolant warms up and circulates under the thermostat, the wax expands and pushes on the piston. This cracks the valve open and allows coolant to begin circulating through the radiator. As the coolant continues to warm up, the valve continues to open until the wide-open temperature is reached. The thermostat has no effect on engine temperature once the coolant temperature is at or above the thermostat’s wide-open temperature.

Most engines use a thermostat with a wide-open temperature of between 190–195 F (87.8–90.6 C). In very cold weather, the thermostat may not fully open. Especially when the vehicle is only operated for a short period of time, the coolant may never reach the wide-open temperature.

Hoses and Tubing. The radiator is fixed to the chassis and stationary. However, the engine moves on its mounts as torque increases and decreases. Therefore, the radiator is usually connected to the engine by flexible hoses. These hoses are made of rubber or neoprene molded around a fiber mesh. Clamps are used to secure the hoses to the radiator and engine.

Some engines have a bypass hose that allows the cool-ant to circulate inside the engine until the thermostat opens. On other engines, the bypass is built into the engine cast-ing or the bypass system is the heater core and hoses. The bypass system prevents damage to rapidly heating parts, such as exhaust valves or cylinder walls, by allowing cool-ant to circulate past the parts before the thermostat opens.

Some cooling systems have fixed metal tubing to route coolant along straight runs. The tubing is either directly connected to components or connected via a flexible hose. This tubing is made of soft steel or aluminum.

Many cooling systems also have one or more small bleeder valves. If a portion of the cooling system is higher than the radiator fill cap, the system will have at least one bleeder valve. Bleeder valves are used to remove air from

Figure 5-20. The coolant reservoir tank is usually mounted in a conspicuous location and can be used as a quick diagnostic tool. Bubbles in the reservoir bottle while the engine is running is a good indication of severe engine problems. Most tanks are not pressurized. Never open a pressurized tank when it is under pressure.

Recovery tank

To radiator overflow neck

Fill levels

Addcoolant

here

Figure 5-21. Parts of a typical thermostat. Most engines use a thermostat with an opening range between 190–195 F(87.8–90.6 C).

Flange

Flange seal

Piston

Nut

Valve seat

Valve

Frame Teflon seal

Wax pellet

Coil spring

Rubber diaphragm


the cooling system during service. Pockets of air in the cool-ing system can block coolant flow, resulting in hot spots or engine overheating.

Engine Belt. An engine belt drives the coolant pump and other engine accessories. The belt is called a serpentinebelt because it winds around several pulleys, Figure 5-22.It is driven by a pulley on the front of the crankshaft. The belt must be in good condition and properly adjusted. Most engines have an automatic tensioner to keep the serpentine belt properly adjusted.

Excessive tightness in the belt places a heavy load on the bearings in the coolant pump and possibly the crank-shaft bearings. This will cause premature wear. Looseness in the belt permits slippage. This can reduce the speed of the coolant pump, alternator, and belt-driven fan. As a result, the engine may overheat or the battery may become discharged. An excessively loose belt will have a tendency to whip or flap, which can cut hoses or cause intermittent loading of the bearings in the coolant pump.

Direct Air CoolingDirect air cooling is a method of directly transferring

engine heat to the surrounding air. It uses a fan to force air around the cylinders and cylinder heads, which are the hot-test parts of the engine. The fan is driven by the crankshaft via a belt. The cylinders and heads of an air cooled engine are made with fins to present a larger heat transfer surface. The engine is surrounded by a sheet metal shroud to direct more air over the hottest engine parts. Air-cooled engines are no longer used on cars and light trucks.

Lubrication SystemThe lubrication system circulates engine oil to internal

engine parts. Engine oil serves several purposes. It must be delivered to the right place at the right time and in the proper quantity. The lubrication system may have no apparent effect on driveability, but it is a vital part of the engine and some defects in it can result in driveability symptoms. Also, some driveability problems can affect the lubrication system.

The various moving parts of the engine are subjected to differing levels of stress. The amount of oil needed var-ies between engine parts. Some parts of the engine are lubricated by pressurized oil, while others are lubricated by splashing oil. Figure 5-23 shows a typical pressure/splash lubrication system.

The camshaft and crankshaft bearings are pressure lubri-cated. Also, hydraulic lifters must have a supply of pressurized oil to work properly. On some engines, pressurized oil drips through nozzles onto moving parts such as timing gears.

Some engine parts can be lubricated by oil that is splashed onto them. Oil is thrown upward by the rotation of the crankshaft. This oil strikes the engine cylinder walls, pis-ton skirts, and piston pins. Some splashed oil also reaches the camshaft and lubricates the cam lobes and valve lifters.

Engine OilThe engine oil, often called motor oil, provides lubrica-

tion between moving parts. Oil is made to do a good job of lubrication, sealing, cooling, shock absorption, and clean-ing. It is also formulated to prevent sludge formation.

Figure 5-22. Engines use one or two serpentine belts to drive all of the accessories. On this hybrid vehicle, a starter/generator is used to restart the engine by driving the belt to turn the crankshaft. (Daimler)

Coolant pump

Serpentine belt

Crankshaft

Starter / generator

Hydraulic belt tensioner

A/C compressor


Lubrication is the most obvious job of engine oil. Oil reduces friction by forming a layer between moving parts. All engine parts, no matter how finely machined, have microscopic high spots. As one part moves across another, these spots will contact each other. As a result, the parts begin to wear and overheat from friction. The oil separates the moving parts, preventing the high spots from touching. The oil acts like a set of microscopic ball bearings, allowing the parts to slide against each other. Friction is greatly reduced.

Cooling is one of the less obvious jobs of engine oil. It is difficult to remove heat from the piston heads. They cannot be cooled by the cooling system, yet the pistons are among the hottest parts in the engine. They will overheat and melt if the heat is not removed. Even a slightly overheated piston can develop a localized hot spot that will cause detonation. Oil splashed under the piston head absorbs heat from the piston. Oil splash also removes heat from the cylinder walls, rods, crankshaft, and other engine parts that cannot be directly cooled by the engine cooling system. The oil itself is cooled by the cooling system and by direct heat transfer when it is in the oil pan.

Sealing is another task of engine oil. A thin film of oil between the piston rings and cylinder wall seals in pressure. If this oil is not present, pressure leakage (loss of compres-sion) will prevent the engine from running.

For some moving parts, such as connecting rod journals and rod bearings, engine oil provides shock absorption. The oil cushions the shock when the rod changes direction at high speeds. This extends bearing life and prevents engine knocking. Other moving parts, such as the piston skirts and cam lobes, are also cushioned by oil.

Cleaning is also an important job of engine oil. Engines constantly collect impurities. Unburned gasoline, carbon from the combustion process, and water vapor get into the crankcase. These impurities can form sludge and varnish deposits in an engine. The deposits can cause the engine to overheat, burn oil, and prematurely wear out. Engine oil contains detergents that prevent formation of sludge by picking up impurities and holding them in suspension. When the oil circulates through the oil filter, the impurities are trapped.

The American Petroleum Institute (API) classifies oil according to various factors that affect oil’s ability to prevent friction and deposits in an engine. The API service classifi-cation is printed on the oil container, Figure 5-24. The API

Figure 5-23. Automotive engines use a combination of pressurized and splashed oil to lubricate engine components. The lubrication system also serves to cool the internal engine components. Note that this engine also uses oil pressure to control a variable timing system. (Ford)

Housing asy-engine variable timing

Housing asy-engine variable

timing LH

Housing asy-engine variable timing

Block asy-cylinder

Adapter asy-oil filter

Oil filter

Camshaftsprocket

bolt

Oil pan asy

Oil pump-screen & cover asy

From head

Back tohead

To chain tensioner

Meteringorifice

Filter

Retard side of variablecamshaft

timing

Tensioner-engine

timing chainAdvance sideof variablecamshaft

timing

Pump asy-oil less screen

& cover

Valvebody asy

Oil to frontof camshaft

timingVariable camshaft timing

auxiliary view

Variable timing asy RHauxiliary view

Oil to rearof camshafttiming rotor

Triggerwheel Enginevariable

camshafttiming asy

From head

Head-cylinder

Engine variablecamshaft timing asy

Tensioner-engine timing

chain LH


service classification is SM for most gasoline engines and CH4 for most diesel engines. Oils with other classifications are only for use in older engines. However, older engines can use engine oil with the newest classification.

In addition to the API grades, the International Lubricants Standardization and Approval Committee (ILSAC), made up of American and Japanese vehicle manu-facturers, classifies oils according to manufacturer test criteria. Classifications are called GF for gasoline fueled. At the present time, GF-4 is the latest standard.

Oil PanOil that drips or is squirted out of any part of the lubri-

cation system eventually drains into the oil pan. The oil panis a reservoir for engine oil and helps the oil to lose the heat that it picked up in the engine. The air passing underneath the vehicle removes this heat from the oil pan, Figure 5-25.Most oil pans have a drain plug at the lowest point of the pan. Some models have two drain plugs.

The oil pan is made of stamped sheet steel or cast alu-minum. Aluminum pans may have cooling fins cast into the bottom. The cast pan also adds some rigidity to the engine block.

Some manufacturers are implementing a dry-sump oiling system. In a dry-sump system, oil that reaches the bottom of the pan is immediately pumped to a separate oil reservoir. This leaves very little oil in the pan. The advan-tage of this system is that it allows the engine to be set lower, which allows a lower hood profile. Dry-sump oiling is a proven system that has been used for many years in auto racing and motorcycles.

Oil Pickup ScreenThe oil pickup screen prevents any large particles,

such as dirt, sand, or metal shavings, from being circulated in the lubrication system. The oil screen is installed on the intake side of the oil pump, Figure 5-26. It is always located at the lowest point in the oil pan. In this way, the screen is always covered by oil. This keeps the oil pump from draw-ing in air if the oil level drops because of oil consumption or sloshing during turns or hard braking.

Since it traps only large particles, the oil screen usually does not become plugged until the engine reaches very high mileage. Most oil screens cannot be removed and cleaned unless the oil pan is removed.

Figure 5-24. A—Oil containers carry an American Petroleum Institute (API) marking indicating the oil viscosity and classifi-cation. B—Oil temperature range chart.

Figure 5-25. The oil pan serves as the reservoir for the engine oil as well as providing a surface for heat dissipation. Most engines have a pan with a single sump. However, some engines use either a dual- or dry-sump pan. (BMW)

Oil pan

Oil pump

Bottom of engine block

B–– – –

A

SM

Figure 5-26. The oil pickup screen is either bolted or pressed onto the oil pump. The pickup reaches into the bottom of the oil pan sump to draw oil into the engine. (Chrysler)

Intake

Oilpump

Oil pickup screen

Bolt


Oil PumpThe engine oil pump develops oil pressure and flow

to circulate oil throughout the lubrication system. Usually, it is driven by a gear on the camshaft or crankshaft. Most gear-driven oil pumps are mounted near the bottom of the engine and connect to the camshaft drive gear through a shaft. Some oil pumps are installed in the engine front cover and are directly driven by the engine crankshaft. The oil pump speed varies with engine speed, since the pump is driven by the engine.

Engine oil pumps are always constant-displacement types. A constant-displacement pump delivers the same amount of oil with each revolution. The faster the pump revolves, the more oil it delivers. Figure 5-27 illustrates the external-gear and rotor designs of oil pump. The external-gear design is most common; however, more and more engines are equipped with rotor pumps.

When the pump gears rotate, the gear teeth unmesh in the inlet area. This creates a low-pressure area that draws oil from the oil pan or oil tank. The oil is carried around the housing in the spaces between the gears and housing. When the gear teeth mesh at the outlet, a high-pressure area is created. The oil is squeezed out of the discharge port. The process is then repeated.

Pressure RegulatorThe oil pump has enough capacity to deliver sufficient

oil pressure and flow at idle speeds. At higher engine speeds, the pump will produce too much oil pressure and flow. This may rupture seals or filter elements, affect hydraulic lifter operation, or cause oil burning.

Oil pump output is controlled by a pressure regulator.The pressure regulator consists of a valve that is held closed by a spring, Figure 5-28. Oil pressure from the pump pushes against the valve on the opposite side from the spring. When the oil pressure reaches a certain point, the spring is com-pressed and the valve opens. This dumps excess oil into the sump, which is at a lower (near atmospheric) pressure. As a

result, the oil pressure is regulated. Engine oil pressure is usu-ally regulated to about 35–45 psi (240–310 kPa). Minimum pressure at idle should be 15–20 psi (105–140 kPa).

Oil FilterThe oil filter removes small particles and contami-

nants from the engine oil. It consists of a stamped metal housing containing, typically, a pleated paper filter ele-ment. Other types of elements may be used. The filter is always installed on the outlet side of the oil pump. Oil under pressure flows into the filter, through the filter ele-ment, and out of the filter.

The oil filter contains an internal bypass. This allows oil to flow past the filter if the element becomes clogged. However, the oil is not filtered when this happens. Some oil filters have an anti-drainback valve. This valve closes to keep oil from draining out of the filter when the engine is not operated for long periods.

The oil filter is replaced during an oil change as part of normal engine maintenance. A typical oil filter, such as the ones shown in Figure 5-29, can be removed from the engine by unscrewing it from the mounting pad. In some engine designs, the oil filter is mounted on the firewall or

Figure 5-27. The oil pump may be of the external gear or rotor design. Both designs have a positive displacement.

Outlet

Inlet

Inlet

Gear

Gear

External gear pump

Outlet

Rotor pump

Internalgear

External gear

Figure 5-28. The pressure regulator controls the maximum oil pressure. Normal oil pressure will not unseat the valve. However, high oil pressure forces the valve open, allowing oil to flow to the pan.

Oil pressure acting on the ball compresses the spring

High oilpressure

Oil flows to the pan

SeatBall

Spring holding the ball against the seat

Normaloil

pressure


elsewhere in the engine compartment. Some oil filters are installed in the oil pan or an engine-mounted canister and do not have housings.

Oil GalleriesOil galleries are internal engine passages that carry

the oil. They are cast or drilled into the engine block and heads. Galleries extend from the pump and filter to the crankshaft and camshaft bearings, valve lifters, and rocker arm shafts. Galleries are drilled in the crankshaft to allow oil to reach the connecting rod bearings. Removable plugs are located at the rear of some engine blocks to allow the galleries to be cleaned during an overhaul.

Gaskets, Seals, and SealantGaskets and seals are used in the intake system to seal

air and fuel in and to prevent vacuum leaks. Preventing fuel and air leaks is vital to driveability, performance, and emissions. Gaskets and seals must stand up to high engine temperatures, but be pliable enough at various operating temperatures to create the intended seal.

Summary

The four-stroke cycle operates through two revolu-tions of the crankshaft. The intake stroke draws air and fuel into the cylinder. The compression stroke compresses the air-fuel mixture. When the mixture ignites, it pushes the piston down for the power stroke. On the exhaust stroke, the upward movement of the piston pushes the exhaust gases out of the cylinder. The cycle then repeats.

The major components of a reciprocating-piston engine are the engine block, pistons and rings, connecting rods, crankshaft, cylinder head(s), valves, and valve train. The valves are driven by the crankshaft through a set of gears, a gear and chain arrangement, or sprockets and a

drive belt. On some engines, valve operation is controlled by a mechanism operated by a computer.

The cooling system removes unwanted engine heat and regulates engine temperature. Cars and light trucks have a liquid cooling system. Coolant is pumped through engine passages by a belt-driven pump. A radiator removes heat from the coolant. Engine coolant is a mixture of anti-freeze and water. Antifreeze may be ethylene glycol or propylene glycol.

Poor lubrication can eventually result in driveability symptoms. The lubrication system circulates engine oil to internal engine parts. Oil galleries are internal passages that carry the oil throughout the engine. The oil pump is driven by a gear on the camshaft or by the engine timing belt. A pressure regulator controls oil pump output. The engine oil provides lubrication, reduces friction, helps with cooling, seals, provides shock absorption between parts, and cleans parts. It is formulated to prevent sludge formation.

Review Questions—Chapter 5

Please do not write in this text. Write your answers on a separate sheet of paper.

1. Name the four strokes in a four-stroke cycle engine.

2. List the major parts installed on or in the engine block.

3. The ______ transfer the force of the expanding combustion gases to the connecting rods.

4. A film of ______ between the compression rings and cylinder wall seals pressure in the cylinder.(A) carbon(B) oil(C) unburned fuel(D) None of the above.

5. The _____ converts the straight-line motion of the piston into rotary motion.(A) piston(B) crankshaft(C) flywheel(D) connecting rod

6. What holds intake and exhaust valves closed?(A) The camshaft.(B) Compression pressure.(C) Valve spring pressure.(D) Expanding combustion gases.

Figure 5-29. Oil filters come in many sizes and shapes. While it is a very simple and inexpensive part, the filter is very important to good engine performance.


7. The camshaft turns at _____ the speed of the crankshaft.(A) about half(B) exactly half(C) about twice(D) exactly twice

8. _____ and ____ are the two general types of variable valve timing.

9. List two devices used to reduce engine vibration.

10. Cars and light trucks manufactured today are _____ cooled.(A) air(B) liquid(C) oil(D) thermostatically

11. The purpose of antifreeze is to:(A) reduce rust and corrosion in the engine and

radiator.(B) lower the freezing point of the engine coolant.(C) increase the boiling point of the engine coolant.(D) All of the above.

12. By pressurizing the cooling system, the boiling point of the engine coolant is _____.

13. Engine oil is used to ______ various parts of the engine.(A) cool(B) lubricate(C) cushion(D) All of the above.

14. Engines are usually lubricated by:(A) pressurized oil.(B) splashed oil.(C) a combination of pressurized/splashed oil.(D) None of the above.

15. Engine oil pressure is controlled by a pressure regulator, typically in the range of:(A) 5–15 psi (35–105 kPa)(B) 15–20 psi (105–140 kPa)(C) 20–35 psi (140–240 kPa)(D) 35–45 psi (240–310 kPa)

ASE Certification-Type Questions1. Technician A says that an engine must have sufficient

compression before it will start and run. Technician Bsays that compression is developed on the power stroke of a four-cycle engine. Who is correct?(A) A only.(B) B only.(C) Both A & B.(D) Neither A nor B.

2. All of the following statements about oil control rings are true, except:(A) oil control rings are installed below the

compression rings.(B) there should be no oil at the compression rings.(C) oil control rings scrape oil from the cylinder

walls when the piston is moving down.(D) defective oil control rings will cause high oil

consumption

3. Technician A says that the intake valves are cooled by incoming air. Technician B says that the intake valve must be in contact with its seat long enough to transfer heat to the cylinder head. Who is correct?(A) A only.(B) B only.(C) Both A & B.(D) Neither A nor B.

4. Cylinder heads contain all of the following, except:(A) intake valves.(B) exhaust valves.(C) EGR valves.(D) camshafts.

5. The valve train is the group of components that opens the ______.(A) intake valves(B) exhaust valves(C) EGR valve(D) Both A & B.

6. A hydraulic lash adjuster, similar in operation to a hydraulic lifter, maintains the proper valve clearance on ______ engines.(A) cam-in-block(B) roller-lifter(C) overhead cam(D) All of the above.


7. Technician A says that overhead camshafts are usually driven by a belt. Technician B says that in cam-in-block, overhead valve engines, the camshaft is usually directly driven by two meshing gears. Who is correct?(A) A only.(B) B only.(C) Both A & B.(D) Neither A nor B.

8. Most vehicle manufacturers recommend a ______ mix of water and antifreeze.(A) 10:90(B) 50:50(C) 30:70(D) 80:20

9. Oil screens on the inlet to the oil pump are to remove:(A) large particles of dirt or metal.(B) small particles of dirt or metal.(C) chemical contaminants.(D) particles the oil filter does not catch.

10. Technician A says that engine oil pumps areconstant-displacement pumps. Technician B saysthat the engine oil pan serves as the reservoir for engine oil. Who is correct?(A) A only.(B) B only.(C) Both A & B.(D) Neither A nor B.


Electricity is used throughout the vehicle. Some vehicles use electricity to assist the gasoline or diesel engine in moving the vehicle. In other vehicles, such as this car from Smart, only electricity propels the vehicle. (Daimler)

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and Operation of Engine Fundamentals 5 - g w · PDF fileChapter 5 Fundamentals of Engine Construction and Operation 75 Pistons and Rings Pistons transfer the force of expanding combustion