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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


Chapter 13

Engine Top End

Construction


Contents

  • Cylinder head construction

  • Valve train construction

  • Intake manifold construction

  • Exhaust manifold construction


Engine Top End

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


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


Cylinder Headand Parts


Cylinder Head Construction

This cast aluminum head has four-valve combustion chambers


Cylinder Head Construction

This cast iron head has a two-valve combustion chamber


Valve Guide Construction

  • There are two basic types of valve guides:

    • integral valve guides

    • pressed-in valve guides


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


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


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


Valve Seats and Guides


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


Valve Seat Angle

Interference angle increases sealing pressure and speeds seating


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


Diesel Prechamber Cup

Area is heated by the glow plug forbetter cold starting


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


Stratified Charge Chamber


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


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


Valve Construction

A. Polished intake valve

B. Stock exhaust valve

C. Hollow exhaust valve is filled with sodium for cooling


Valve Face Angle

  • Angle formed between the valve face and valve head

  • Normal valve face angles are 45º and 30º


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


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


Stellite Valve

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


Valve Seal Construction

  • Valve seals come in two basic types:

    • umbrella valve seals

    • O-ring valve seals


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


Umbrella Valve Seal

A. Synthetic rubber seal with plastic shedder insert

B. All synthetic rubber seal

C. Plastic valve seal


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


O-ring Valve Seal


Nylon Shedder

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


Valve Spring Construction

This dual coil spring is designed toincrease spring pressure


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


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


Valve Retainers and Keepers

Used to lock the valve springonto the valve


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


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


Valve Rotators

This engine uses a valve rotator for each exhaust valve


Valve Rotators

This engine uses a valve rotatorfor each valve


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


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


Camshaft

With dual overhead cam engines, there are two camshafts


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


Cam Lobe


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


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


Valve Timing


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


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


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


Cam Bearings

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


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


Valve Lifters

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


Hydraulic Lifters

Operate quietly by maintaining zerovalve clearance


Hydraulic Lifters

Lifter adjusts automatically with temperature changes and part wear


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


Hydraulic Lifter Operation


Mechanical Lifters

Transfer cam lobe action to the push rod


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


Roller Lifters

Small roller rides on the camshaftlobe to reduce friction


OHC Follower

Fits between the camshaft and valve


OHC Follower Components


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


Push Rods

Inline engine using a pivot ball tohold the rocker arm


Push Rod Guide Plates

Used to limit side movementof the push rods


Rocker Arms

Transfer valve train motion to thevalve stem tips


Pivot Balls (Stands)

Used to hold the rocker arm inplace over the valve


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


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


Intake Manifold

Construction


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


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


Fluid Induction Assembly

Takes the place of a traditionalintake manifold

Fig 31


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


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


Variable Induction System

  • Provides increased engine efficiency and performance

  • Uses two sets of intake runners controlled by butterfly valves

  • Butterfly valves are computer-controlled


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


Exhaust Manifold

Construction


Exhaust Manifold

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

  • Made of cast iron or steel tubing


Manifolds

Intake and exhaust manifolds with their related components


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