Engine Upper End

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: • 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 • 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 • 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 • 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 • 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 • 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