Chapter_18_Engine_Upper-End__Revised_

Chapter 18: Engine Upper End

Learning Objectives

• Identify all parts of the engine's upper end.

• Understand differences in cylinder head designs.

• Comprehend variations in camshaft design.

• Describe different camshaft lobe profiles and their applications.

• Identify cam drive arrangements.

• Explain the difference between freewheeling and non-freewheeling engines.

Introduction to Engine Upper End

• The upper end of an engine includes:

  • Cylinder head(s)

  • Valve train: Consists of camshaft and cam drive.

• Intake and exhaust manifolds are discussed in another chapter.

Cylinder Head Construction

• Made from:

  • Cast iron

  • Aluminum

• Bare head: Head without installed components.

• Components of the cylinder head include:

  • Intake and exhaust valves

  • Retainers and valve locks

  • Valve guide seals

  • Valve springs

  • Rocker arms

Valve Guides

• Function: Guides valves during opening and closing.

• Types:

  • Integral: Only used in cast iron heads.

  • Replaceable inserts: Found in some iron and all aluminum heads.

• Worn valve guides can increase oil consumption.

Valve Guide Seals

• Leaking valve guides contribute to nearly half of oil consumption issues.

• Seal materials differ in high-temperature resistance.

• Valve seats can be integral or replaceable.

Valves

• Poppet valves are standard in automotive applications.

• Intake valves are 35%-40% larger than exhaust valves and function at high temperatures.

• Materials: Typically different for intake and exhaust valves.

• Valve stems are often chrome-coated to enhance durability.

• Heavy-duty engines may use sodium-filled valves which help manage high temperatures.

Retainers and Keepers

• Retainers and valve locks hold the spring and valve together.

• Keepers fit into grooves on the valve stem.

• Retainer's role: Holds spring against spring seat on top of the cylinder head.

• Valve rotators: Facilitate valve rotation for improved heat removal.

Valve Springs

• Function to close the valve; some engines require heavier springs.

• Dampeners are sometimes included to reduce spring vibrations.

Pushrods and Rocker Arms

• Cam-in-block engines utilize pushrods and rocker arms to transfer motion.

• Rocker arms may have varying ratios affecting lift.*

• Some OHC engines incorporate rocker arms directly.

Camshaft

• Controls valve operation; typically crafted from hardened cast iron.

• Supports via cam journals.

Number of Cams and Lobes

• Cam configuration is determined by the number of valves.

• Generally, one camshaft per cylinder head is common, but high-performance engines may require different setups.

Camshaft Performance

• Design considerations directly affect engine efficiency and performance.

• Two main factors affecting cam performance:

  • Duration: Length of time the valve is open.

  • Lift: The height to which the valve opens.

• Volumetric Efficiency: Corresponds to effective air and fuel intake.

Valve Lifters and Lash Adjusters

• Lifters ride on the cam lobes for effective valve operation.

• Some engines, like OHC, have hollow camshafts with oil passageways.

Roller Cam and Lifters

• Roller lifters significantly reduce friction in the valve train, enhancing horsepower and fuel economy.

Hydraulic Lifters

• Automatically maintain zero lash; designed for quiet operation and reduced wear.

Camshaft Drives

• Various methods exist to drive the camshaft:

  • Gear drive

  • Sprockets with timing chain/belt

• Freewheeling vs. interference engines:

  • Freewheeling: Piston and valves do not collide.

  • Interference: Collision can occur.

Valve Timing

• Critical to engine timing; specific opening and closing points are crucial for performance.

• Valve overlaps allow smoother operation and enhance performance.

Variable Valve Timing

• Used widely for horsepower enhancement and emissions control.

• Systems vary in complexity, impacting both timing and lift.

Electric Cam Phasers

• More complex systems combining variable lift and timing with hydro-mechanical interaction.

Active Fuel Management

• Types of systems aim to increase fuel economy via cylinder deactivation.

• Some systems use solenoids or electrohydraulic methods to control valve operation.