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Modern Automotive Technology by Russell Krick Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois PowerPoint for Chapter 13 Engine Top End Construction Contents Cylinder head construction Valve train construction Intake manifold construction Exhaust manifold construction

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Modern Automotive

Technology

by

Russell Krick

PublisherThe Goodheart-Willcox Co., Inc.Tinley Park, Illinois

PowerPoint for


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Chapter 13

Engine Top End

Construction


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Contents

  • Cylinder head construction

  • Valve train construction

  • Intake manifold construction

  • Exhaust manifold construction


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Engine Top End

Includes the cylinder head, valve train, valve cover, and intake and exhaust manifolds


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Cylinder Head

Construction

  • A bare cylinder head is a head casting with all of its parts removed

  • If a cylinder head becomes damaged, the technician may need to install a new bare head

  • All of the old, reusable parts can be removed and installed in the new head


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Cylinder Headand Parts


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Cylinder Head Construction

This cast aluminum head has four-valve combustion chambers


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Cylinder Head Construction

This cast iron head has a two-valve combustion chamber


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Valve Guide Construction

  • There are two basic types of valve guides:

    • integral valve guides

    • pressed-in valve guides


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Integral Valve Guide

  • Part of the cylinder head casting

  • Simply a hole machined through the cylinder head

  • Very common because of its low production cost


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Pressed-in Valve Guide

  • Separate sleeve forced into an oversize hole machined in the cylinder head

  • Made of cast iron or bronze

  • During repair, a worn guide can be pressed out, and a new guide quickly pressed in


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Valve Seat Construction

  • Valve seats can be integral or pressed-in

  • Integral valve seat

    • machined portion of the cylinder head casting

  • Pressed-in valve seat

    • separate part that is forced into a recess cut into the head

    • commonly used in aluminum heads



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Valve Seat Angle

  • Angle formed by the face of the seat

  • Most engines use a 45º angle

  • Some high-performance engines use seat angles of 30º


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Valve Seat Angle

Interference angle increases sealing pressure and speeds seating


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Diesel Prechamber Cup

  • Pressed into the cylinder head of some diesel engines

  • Holes are machined into the deck

  • Prechambers are force-fit into these holes

  • Each prechamber forms an enclosure around the tip of an injector and glow plug


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Diesel Prechamber Cup

Area is heated by the glow plug forbetter cold starting


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Stratified Charge Chamber

  • Fits into the cylinder head casting to form an auxiliary chamber

  • Uses a rich fuel mixture in the auxiliary chamber to ignite a lean mixture in the main combustion chamber



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Valve Train Construction

  • The valve train controls the opening and closing of the cylinder head ports

  • Construction will vary with engine design

  • To be able to work on any type of valve train, you must understand these differences


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Valve Construction

  • Automotive engines commonly use poppet valves

  • Some valve stems are chrome plated to better resist wear

  • Grooves are cut into the valve stem tops for the keepers


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Valve Construction

A. Polished intake valve

B. Stock exhaust valve

C. Hollow exhaust valve is filled with sodium for cooling


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Valve Face Angle

  • Angle formed between the valve face and valve head

  • Normal valve face angles are 45º and 30º


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Sodium-Filled Valves

  • Used when extra valve cooling action is needed

  • During operation, the sodium inside the hollow valve melts, becoming a liquid

  • This liquid is used to cool the valve


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Sodium-Filled Valves

  • When the valve is opened, the sodium splashes down into the head and collects heat

  • When the valve is closed, the sodium splashes up into the stem

  • Heat transfers out of the sodium and into the stem, valve guide, and engine coolant


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Stellite Valve

Stellite coating on its face retards wear and allows the use of unleaded gasoline


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Valve Seal Construction

  • Valve seals come in two basic types:

    • umbrella valve seals

    • O-ring valve seals


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Umbrella Valve Seal

  • Shaped like a cup

  • Made of neoprene rubber or plastic

  • Slides down over the valve stem before the spring and retainer

  • Covers the small clearance between the valve stem and guide

  • Keeps oil from being drawn into the cylinder head combustion chamber


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Umbrella Valve Seal

A. Synthetic rubber seal with plastic shedder insert

B. All synthetic rubber seal

C. Plastic valve seal


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O-ring Valve Seal

  • Small round seal that fits into an extra groove cut in the valve stem

  • Seals the gap between the retainer and valve stem

  • Stops oil from flowing though the retainer, and down the stem

  • Fits onto the valve stem after the spring and retainer



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Nylon Shedder

May be used to limit the amount of oil that splashes on the valve stem


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Valve Spring Construction

This dual coil spring is designed toincrease spring pressure


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Valve Spring Terminology

  • Spring tension

    • stiffness of a valve spring

    • service manual will give the tension in pounds or kilograms for specific compressed lengths

  • Spring free length

    • length of the spring when removed from the engine


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Valve Spring Shim

  • Very thin, accurately machined washer used to increase spring tension

  • When a shim is placed under a spring, the open and closed lengths of the spring are reduced

  • Provides a means of restoring full spring pressure without spring replacement


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Valve Retainers and Keepers

Used to lock the valve springonto the valve


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Valve Spring Seat

  • Cup-shaped washer installed between the cylinder head and the bottom of the valve spring

  • Provides a pocket to hold the bottom of the valve spring


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Valve Rotators

  • Turn the valves to prevent carbon buildup and hot spots on the valve faces

  • May be located under or on top of the valve spring

  • Commonly used on exhaust valves, which are exposed to more heat than intake valves


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Valve Rotators

This engine uses a valve rotator for each exhaust valve


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Valve Rotators

This engine uses a valve rotatorfor each valve


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Valve Stem Cap

  • May be placed over the end of the valve stem

  • Helps prevent stem and rocker arm wear

  • Free to turn on the valve stem

  • Serves as a bearing that reduces friction

  • May be used to adjust clearance in the valve train


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Camshaft

  • Controls when the valves open and close

  • May be driven by gears, a chain, or a belt

  • There may be one or two camshafts per cylinder head


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Camshaft

With dual overhead cam engines, there are two camshafts


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Cam Lobes

  • Precision-machined and polished surfaces on the camshaft

  • Variations in lobe shape control:

    • when each valve opens in relation to piston position

    • how long each valve stays open

    • how far each valve opens



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Camshaft Terminology

  • Camshaft lift

    • how far the valve opens

  • Camshaft duration

    • how long the valve stays open

  • Valve timing

    • valve opening and closing in relation to the position of the pistons


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Camshaft Terminology

  • Variable valve timing

    • engine can alter when the valves open with engine speed

  • Valve overlap

    • time when both the intake and exhaust valves in the same cylinder are open

    • used to improve the movement of gases through the engine



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Dual Cam Lobes

  • Some camshafts are machined with dual cam lobes that have two different profile shapes

    • one lobe is designed for low-speed efficiency while the other lobe is designed for high-speed efficiency

  • ECM operates a solenoid valve that controls oil flow to shift the rocker arms from one lobe profile to the other


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Hollow Camshafts

  • Have their lobes pressed onto the shaft

  • To lock the lobes in place, an oversize steel ball is forced down through the center of the hollow shaft

  • Produces a light-weight camshaft


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Camshaft Thrust Plate

  • Used to limit camshaft end-play

  • Bolts to the front of the block or cylinder head

  • When the drive gear or sprocket is bolted in place, the thrust plate sets up a predetermined camshaft end play


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Cam Bearings

One- or two-piece inserts that are pressed into the block or cylinder head


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Cam Housing and Cover

  • Cam housing

    • casting that bolts to the top of the cylinder head to hold the camshaft

    • used in some overhead cam engines

  • Cam cover

    • lid over the top of the cam housing

    • prevents valve train oil spray from leaking out of the engine


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Valve Lifters

Ride on the camshaft lobes andtransfer motion to the other partsof the valve train


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Hydraulic Lifters

Operate quietly by maintaining zerovalve clearance


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Hydraulic Lifters

Lifter adjusts automatically with temperature changes and part wear


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Hydraulic Lifter Operation

  • Charging cycle

    • when the valve closes, oil rushes into the lifter, pushing up on the internal disc or plunger to maintain zero clearance

  • Leak-down cycle

    • when the cam acts on the lifter, oil is trapped in the lifter by a check valve

    • lifter acts as a solid unit to push the valve open



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Mechanical Lifters

Transfer cam lobe action to the push rod


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Mechanical Lifters

  • Do not contain oil

  • Periodic adjustment is required

  • Adjustment is normally provided at the rocker arm

  • Small valve train clearance needed causes clattering or clicking noise when the valves open and close


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Roller Lifters

Small roller rides on the camshaftlobe to reduce friction


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OHC Follower

Fits between the camshaft and valve



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Push Rods

  • Metal tubes or rods with specially formed ends

  • Used in cam-in-block engines to transfer motion from the lifters to the rocker arms


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Push Rods

Inline engine using a pivot ball tohold the rocker arm


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Push Rod Guide Plates

Used to limit side movementof the push rods


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Rocker Arms

Transfer valve train motion to thevalve stem tips


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Pivot Balls (Stands)

Used to hold the rocker arm inplace over the valve


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Adjustable Rocker Arms

  • Used to change the valve train clearance

  • Either a screw is provided on the rocker arm or the rocker arm pivot point can be changed

  • Must be used with mechanical lifters


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Nonadjustable Rocker Arms

  • Have no means of changing valve clearance

  • Used only with some hydraulic lifters

  • Rocker arm assembly is tightened to a specified torque

    • presets the lifter plunger halfway in its travel

  • Push rod length can be changed for clearance adjustments


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Intake Manifold

Construction


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Intake Manifold

  • Holds the throttle body and has passages, called runners, going to each cylinder head port

  • May contain water jackets for cooling

  • Cast of iron, aluminum, or plastic


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Manifold Runners

  • Carry either the air-fuel mixture or air to the cylinder head ports

  • Exhaust passages warm the manifold and allow for exhaust gas recirculation


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Fluid Induction Assembly

Takes the place of a traditionalintake manifold

Fig 31


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Composite Manifolds

  • Intake manifolds can be made of glass-filled nylon or plastic

  • These weigh half as much as aluminum

  • Plastic runners are smoother than metal on the inside, improving airflow

  • Brass thread inserts are molded into the plastic allowing parts to be bolted to the manifold


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Flame Arrester

  • Located between the air filter and the engine intake manifold

  • Prevents backfire damage to the air filter

  • Made of metal mesh to prevent the flame of a backfire from entering the air filter housing


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Variable Induction System

  • Provides increased engine efficiency and performance

  • Uses two sets of intake runners controlled by butterfly valves

  • Butterfly valves are computer-controlled


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Variable Induction System

  • At low engine speeds, the system uses the longer intake runners, improving low-end torque

  • When a specific engine speed is reached, the computer opens the butterfly valves over the shorter intake runners

  • Airflow is increased for added power


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Exhaust Manifold

Construction


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Exhaust Manifold

  • Routes burned exhaust gases from the cylinder head exhaust port to the exhaust pipe

  • Made of cast iron or steel tubing


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Manifolds

Intake and exhaust manifolds with their related components


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