Modern Automotive Technology PowerPoint for by Russell Krick Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

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

Cylinder Head and Parts

Cylinder Head Construction This cast aluminum head has four-valve combustion chambers

Cylinder Head Construction This cast iron head has two-valve combustion chambers

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 a 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 can be 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

An interference angle increases sealing pressure and speeds seating Valve Seat Angle An 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

Area is heated by the glow plug for better cold starting Diesel Prechamber Cup Area is heated by the glow plug for better 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 port and 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 through the retainer, down the stem, and into the guide Fits onto the valve stem after the spring and retainer

O-Ring Valve Seal

Used to limit the amount of oil that splashes on the valve stem Nylon Shedder Used to limit the amount of oil that splashes on the valve stem

Valve Spring Construction This dual coil spring is designed to increase 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 spring onto 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

This engine uses a valve rotator for each exhaust valve Valve Rotators This engine uses a valve rotator for each exhaust valve

This engine uses a valve rotator for each valve Valve Rotators This engine uses a valve rotator for 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 In dual overhead cam engines, there are two camshafts per cylinder head

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 Camshaft duration Valve timing 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 Valve overlap 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 The 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 lightweight 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 installed in the block or cylinder head

Cam Housing and Cover Cam housing Cam cover 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 and transfer motion to the other parts of the valve train

Operate quietly by maintaining zero valve clearance Hydraulic Lifters Operate quietly by maintaining zero valve clearance

Hydraulic Lifters The 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

Transfer cam lobe action to the push rod 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

A small roller rides on the camshaft lobe to reduce friction Roller Lifters A small roller rides on the camshaft lobe to reduce friction

Fits between the camshaft and valve 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

An inline engine using a pivot ball to hold the rocker arm Push Rods An inline engine using a pivot ball to hold the rocker arm

Used to limit side movement of the push rods Push Rod Guide Plates Used to limit side movement of the push rods

Transfer valve train motion to the valve stem tips Rocker Arms Transfer valve train motion to the valve stem tips

Used to hold the rocker arm in place over the valve Pivot Balls (Stands) Used to hold the rocker arm in place 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 The 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

“Ram Manifold” Assembly Takes the place of a traditional intake manifold

Composite Manifolds Intake manifolds can be made of glass-filled nylon or plastic Weighs 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

Intake and exhaust manifolds with their related components