1. Engine Upper End
Chapter 18

2. Objectives Identify all of the parts of the engine's upper end
Understand the difference between cylinder head designs
Understand the variations in camshaft design
Describe different camshaft lobe profiles and their uses
Identify the different cam drive arrangements
Describe the difference between freewheeling and non-freewheeling engines

3. Introduction Upper end includes: Intake and exhaust manifolds
Cylinder head and heads
Valve train (camshaft and cam drive)
Intake and exhaust manifolds
Covered in another chapter

4. Cylinder Head Construction
Made of either cast iron or aluminum
Bare head
Head without other parts installed
Other parts
Intake and exhaust valves
Retainers and valve locks
Valve guide seals
Valve springs
Rocker arms

6. Valve Guides Tube in cylinder head Worn valve guides
Guides valves open and closed
Types: integral and replaceable insert
Integral guides: only used in cast iron cylinder heads
Some iron heads and all aluminum heads have replaceable inserts
Worn valve guides
Affect oil consumption

8. Valve Guide Seals Leaking valve guides
Account for nearly half of oil consumption complaints
Valve guide seals are made of several materials
Different resistances to high temperatures
Valve seats
Can be integral or replaceable

10. Valves Automotive valves are poppet valves
Intake valves: 35%-40% larger than exhaust valve
Run at high temperatures
Usually made of different materials
Valve stems are often chrome coated
A burned valve will cause misfires
Some heavy-duty engines use sodium-filled valves
Valve stem tip is hardened

12. Retainers and Keepers Retainers and valve locks Keepers Retainer
Hold the spring and valve together
Keepers
Fit into the groove in valve stem
Retainer
Holds spring against spring seat on top of cylinder head
Valve rotators
Cause valve to rotate
Aids in heat removal

13. Valve Springs Closes the valve Stronger spring tension
Some engines have heavier valve springs
Stronger spring tension
Two springs are used
Some springs have a flat wound dampener
Dampens spring vibrations

14. Pushrods and Rocker Arms
Cam-in-block engines
Use pushrods and rocker arms to transmit motion from the cam lobes to the valves
Rocker arms may have different rocker arm ratios
Some OHC engines use rocker arms

16. Camshaft Controls opening and closing of valves
Usually made of hardened cast iron
Cam journals support the camshaft

17. Number of Cams and Lobes
Depends on number of valves that need to be opened
Usually two cam lobes for each cylinder
Many engines only use one camshaft per cylinder head
Some high-performance engines have four valves per cylinder
Intake and exhaust lobes
Two camshafts for each cylinder
Two lobe types per cylinder

19. Camshaft Performance Design determines how well an engine breathes
Production engine: balance between best operation at maximum power and high speed or better fuel economy and low-speed operation
Volumetric efficiency: the more air and fuel drawn into the cylinder in the correct proportion, the more power an engine can produce
Base circle: cam without lobe
Factors of cam lobe profile: duration and valve lift
Mechanical valve lash adjustment: cams have a clearance ramp at lobe beginning and end

21. Valve Lifters and Lash Adjusters
Lifter: rides on cam lobe
Cam follower: rides on OHC engine lobe
Lifter's convex shape prevents edge loading
OHC engines have hollow camshafts with oil holes

22. Roller Cam and Lifters Roller lifter Roller camshaft
Cuts valve train friction almost in half
Results in increased horsepower and fuel economy
Roller camshaft
Made of steel
Lobes have a different shape
Allows faster acceleration rates
Valves can be opened faster

23. Hydraulic Lifters
Eliminate need for periodic valve adjustments, are quiet, and reduce valve train wear
Automatically maintain zero-lash
Construction
Consists of a plunger, plunger return spring, and check valve assembly
Operation
Whenever clearance occurs, a spring between plunger and lifter body causes lifter to expand

24. Camshaft Drives Camshaft is driven by the crankshaft by:
Gear drive
Sprockets and timing chain
Sprockets and timing belt
Sprockets and gears
Made of steel, iron, aluminum, or fiber
Timing chains
Roller chain and Morse-type silent chain
Have a drive side and an opposite side where slack accumulates

25. Camshaft Drives (cont'd.)
Freewheeling engines
Pistons and valves cannot contact each other
Interference engines
Pistons and valves collide
Timing belts
Camshafts on some OHC engines are driven by a timing belt
Several advantaged over chain drives

26. Valve Timing Key points Intake must open before TDC
Stays open longer after BDC
Exhaust valve must open long before end of power stroke
Allowed to remain open past TDC

27. Valve Timing (cont’d.) Valve overlap: degrees of crankshaft rotation
Occurs while valves are open at the same time
Most cams are ground with four- to six-degree advance
Better low-end torque
Compensates for timing chain stretch

28. Variable Valve Timing Most manufacturers use variable valve timing
Inexpensive way to increase horsepower and control emissions
Variable timing and lift system
Each pair of valves has three cam lobes

29. Variable Valve Timing (cont'd.)
Variable camshaft phasing
Some VVT systems vary only valve timing but not the lift and duration as described previously
Variable timing and lift plus cam phasing
More complex VVT systems combine VVT and lift with variable camshaft phasing
Atkinson cycle engine
Design used in some hybrid vehicles

30. Active Fuel Management/ Displacement on Demand
Means of increasing fuel economy
Engine runs on all of its cylinders when idling
Smooth operation
Valve control using solenoids
Some systems control cam timing using electric solenoid actuators
Directly control valves