1. Cylinder Head Components
CHAPTER 12
Cylinder Head Components

2. Introduction The cylinder head is an integral part of the engine.
End cap for combustion chamber
Admits air and fuel and exhausting gases
Prevents engine from overheating

3. Cylinder Heads (Gasoline Engines) (1 of 14)
Intake of air/fuel
Compression of air/fuel
Ignition of air/fuel
Power stroke
Exhaust of burned gases

4. Cylinder Heads (Gasoline Engines) (2 of 14)
Cylinder heads can be made of cast iron or aluminum alloy.
In most vehicles today, made of aluminum

5. Cylinder Heads (Gasoline Engines) (3 of 14)
In overhead valve (OHV) engine, valves positioned in cylinder head assembly directly over top of piston.

6. Cylinder Heads (Gasoline Engines) (4 of 14)
In OHC engine, camshaft inside cylinder head, directly actuates valves via cam followers or rocker arms.
More expensive cam drive and enhanced oiling

7. Cylinder Heads (Gasoline Engines) (5 of 14)
Dual overhead cam (DOHC) engine contains two camshafts per cylinder head.
One camshaft operates intake valves; the other operates exhaust valves.

8. Cylinder Heads (Gasoline Engines) (6 of 14)
Cylinder head is composed of many distinct parts.
Bare cylinder head casting
Intake valves
Exhaust valves
Valve keepers
Valve retainer

9. Cylinder Heads (Gasoline Engines) (7 of 14)
Cylinder head is composed of (cont’d):
Valve springs
Oil seals
Valve stem seals
Rocker arms
Plugs (galley, coolant)
Camshaft

10. Cylinder Heads (Gasoline Engines) (8 of 14)
Combustion chamber inside engine is where fuel and air are compressed by piston then ignited by spark plug.
Formed into cylinder head during casting process
Efficiency determined by design

11. Cylinder Heads (Gasoline Engines) (9 of 14)
Improve swirl and turbulence of air/fuel mixture
Shape and angle of intake port
Turbulence increased in quench/squish area
Squishing air/fuel into small charge

12. Cylinder Heads (Gasoline Engines) (10 of 14)
Hemispherical cylinder 1901
Intake valve on one side; exhaust valve on other
Good cross-flow of gases
Spark plug near center of chamber
Flame front = flame propagation

13. Cylinder Heads (Gasoline Engines) (11 of 14)
Bathtub combustion chamber oval, shaped like an inverted bathtub
Valves mounted vertically side by side

14. Cylinder Heads (Gasoline Engines) (12 of 14)
Wedge combustion chamber tapers away from spark plug.
Valves straight line positioned along tapered angle
Speeds velocity of flame front

15. Cylinder Heads (Gasoline Engines) (13 of 14)
Gas direct injection (GDI) cylinder head
Gas injected directly into combustion chamber
Controls fuel
Improves fuel economy by 35%

16. Cylinder Heads (Gasoline Engines) (14 of 14)
Size of intake and exhaust ports in cylinder heads affect engine output.
Smaller intake and exhaust ports allow engine to develop more torque at low engine speeds.
Larger intake and exhaust ports allow greater airflow during engine’s high-speed operation.

17. Valves and Valve Trains (1 of 22)
Valve trains are responsible for moving air and fuel through engine.
Experience enormous stress even under normal circumstances

18. Valves and Valve Trains (2 of 22)
Valve tip
Keeper groove
Valve stem
Valve face
Valve head
Valve margin

19. Valves and Valve Trains (3 of 22)
A four-valve arrangement usually has two intake and two exhaust valves

20. Valves and Valve Trains (4 of 22)
Poppet (mushroom) valve
Pops up/down to open and seal
Red-hot under high-power conditions
Stands up to spring and combustion pressure
Hollow stems

21. Valves and Valve Trains (5 of 22)
Intake valves are made of steel mixed with chromium or silicon to make them more resistant to corrosion.

22. Valves and Valve Trains (6 of 22)
Valve guides are hollow metal passageways.
Valve moves up and down only.
Must retain lubrication
Cannot be lubricated with insufficient clearance

23. Valves and Valve Trains (7 of 22)
Integral valve guide (non-replaceable valve guide)
Cannot be removed or replaced
Repaired by machining it and installing a thin wall bronze liner

24. Valves and Valve Trains (8 of 22)
Non-integral valve guide (replaceable valve guide)
Removed and replaced as needed for repairs
Cast iron or bronze

25. Valves and Valve Trains (9 of 22)
Valve stem seals used on intake and exhaust valves
Control oil that lubricates valve stems
Allow just enough oil to lubricate valve stems and guides

26. Valves and Valve Trains (10 of 22)
Cylinder heads have one of three types of valve seals.
Umbrella-style
O-ring
Positive

27. Valves and Valve Trains (11 of 22)
An O-ring valve stern seal.
A positive valve stern seal.

28. Valves and Valve Trains (12 of 22)
Valve seat mates with face of valve.
Hardened steel
Compatible with today’s gasoline
Ground or cut
Seal tightly
Interference angle for quick bedding-in

29. Valves and Valve Trains (13 of 22)
Valve train controls opening and closing.
OHV
OHC
DOHC

30. Valves and Valve Trains (14 of 22)
Camshafts provide motion to open and close.
Cam lobes
Lift
Duration
Lobe separation angle

31. Valves and Valve Trains (15 of 22)
Engine lifter in the engine block and cylinder head.
Engine lifter in between the cam and the valve tip (bucket style)

32. Valves and Valve Trains (16 of 22)
Most OHC use camshaft.
Same function as rocker arm
Pivot on one end; slider or roller near center

33. Valves and Valve Trains (17 of 22)
If camshaft is on top of valves, engine will use bucket-style lifters.
Hydraulic or mechanical

34. Valves and Valve Trains (18 of 22)
OHV engines incorporate pushrods to transfer motion from valve lifter to rocker arm.
Ball to ball
Ball to cup
Ball to adjustable tip

35. Valves and Valve Trains (19 of 22)
Rocker arm pivots inward.
Direction change
OHV or OHC
Different ratios
Different styles
Stamped, cast, or forged

36. Valves and Valve Trains (20 of 22)
Valve springs close valves and hold valve firmly against valve seat.
Coil spring
Must meet specs
One spring or multiple springs

37. Valves and Valve Trains (21 of 22)
Valve spring retainers are used along with valve keepers to hold valve spring in place.
Steel
Valve rotator
Exhaust valves

38. Valves and Valve Trains (22 of 22)
Valve keepers (valve locks) lock valve system to retainer.
Split taper design
Hardened to withstand opening and closing valves

39. Gaskets (1 of 8)
Gaskets form seal by being compressed between stationary parts where liquid or gases could pass.
Generally designed to be single use

40. Gaskets (2 of 8) Made of soft materials. Cork Rubber Paper Brass
Copper
Aluminum
Stainless steel

41. Gaskets (3 of 8)
Gaskets today are made from vulcanized rubber or EPDM.
Some gasket materials swell once put into service to increase sealing ability.

42. Gaskets (4 of 8)
Head gaskets seal and contain pressures of combustion within engine, seal oil passages, and control flow of coolant.
Anisotropic
Provide or adjust proper clearances

43. Gaskets (5 of 8) Some incorporate stainless steel fire rings.
Late-model vehicles have a multilayer steel (MLS) head gasket.

44. Gaskets (6 of 8) Oil seals seal rotating parts of engine.
Valve stem seal uses similar sealing principle.
Stationary or sliding shafts can be sealed using O-rings.
Seal two surfaces in stationary contact with each other.

45. Gaskets (7 of 8) RTV silicone is one of most popular types.
Only to fill gaps with small amount
Oxygen sensor-safe RTV on engines with oxygen sensors

46. Gaskets (8 of 8) Contact cement is most popular adhesive.
Valve cover gaskets
Fuel pump gaskets
Intake and exhaust manifold gaskets

47. Cylinder Head Diagnosis
Cylinder head problems can affect engine function.
Cracking
Holes
Leaking
Warped cylinder head
Burnt or warped valves
Stripped spark plug hole threads

48. Cylinder Head Repair (1 of 4)
Thermal stress is main cause of cylinder head cracking.
Removing cylinder heads should only be done after extensive testing.
Always clean cylinder head after removal.

49. Cylinder Head Repair (2 of 4)
Valves and valve seats should always be inspected when cylinder head is removed from engine.
Valves and valve guides should be measured.
Correct size and strength of valve springs are critical to engine operation.

50. Cylinder Head Repair (3 of 4)
Cylinder head will need to be reassembled after work on valves, springs, and head is complete.
Pushrods and rocker arms should be inspected at each point of contact.
If camshaft is being reused, measure and inspect cam lobes and journals.

51. Cylinder Head Repair (4 of 4)
Camshaft bearings support camshaft and are critical to operation.
When installing camshafts on bucket lifter head, install intake camshaft on the intake valves and exhaust camshaft on exhaust valves.
Heads that use cam followers or rocker arms begin with installation of camshaft, or rocker arms might need to be installed first.

52. Summary (1 of 17)
Functions of the cylinder head include: admit air and fuel to combustion chamber, release exhaust after combustion, and allow coolant to flow around the top of the combustion chamber.
The cylinder head forms the top of the combustion chamber and is securely fastened with a head gasket.

53. Summary (2 of 17)
Cylinder heads may be aluminum alloy (lighter weight, boosts fuel economy) or cast iron (heavier, but lower engine operating temperatures).
Engines may be overhead valve, overhead cam, or dual overhead cam.

54. Summary (3 of 17)
Cylinder head parts include: base cylinder head casting, intake valves, exhaust valves, valve keepers, valve retainers, valve springs, oil seals, coolant seals, rocker arms, plugs, and camshaft.
Cylinder heads improve the swirl and turbulence of the air/fuel mixture moving into the combustion chamber. 54

55. Summary (4 of 17)
A hemispherical (HEMI) combustion chamber has intake and exhaust valves located on opposite sides to create cross flow of gases.
The amount of air an engine can take in and remove is referred to as “breathing.”
The greater the air/fuel mixture, the more heat is generated, and thus more engine power.

56. Summary (5 of 17)
Dual overhead cam engines often have multivalve cylinder heads to create quicker, more efficient air/fuel movement.
Cylinder head shapes can be oval (bathtub), wedge, or gas direct injection (GDI).

57. Summary (6 of 17)
Smaller intake and exhaust ports are generally better for vehicles operating in low gear (four-wheel drive), while larger intake and exhaust ports are ideal for engines operating at high speeds.
Components of the valve train are driven from the camshaft and include: lifters, pushrods, rocker arms or cam followers, valves, valve springs, keepers, and retainers.

58. Summary (7 of 17)
Components of the valve are: valve tip, keeper grooves, valve stem, valve face, and valve margin.
Valves are located in the cylinder head and are configured in two-, three-, four-, and five-valve arrangements.
Most vehicles are fitted with poppet (mushroom) valves.

59. Summary (8 of 17)
Exhaust valves are designed to withstand higher temperatures than intake valves.
Valve guides are integral (non-replaceable) or non-integral (replaceable) and are designed to limit a valve’s movement to up-and-down and retain lubrication for the valve stem.

60. Summary (9 of 17)
Valve stem seals are designed to prevent oil leakage; the three basic types are umbrella style, O-ring, and positive.
Valve seals form a strong seal with the valve face and must withstand high temperatures and extreme pressure.
Valve train refers to all the parts that contribute to the opening or closing of the intake and exhaust valves.

61. Summary (10 of 17)
Types of valve trains correspond to engine types: overhead valve, overhead cam, or duel overhead cam.
Rocker arms are categorized by the ratio of movement on the valve side to movement on the push rod side.

62. Summary (11 of 17)
Push rods, found in overhead valve engines, transfer the motion from the valve lifter to the rocker arm; push rod types are: ball-to-ball, ball-to-cup, and ball-to-adjustable tip.
Lifters can be solid (manually adjusted) or hydraulic (self-adjusting) and are located in the engine block, cylinder head, rocker arms, and between the cam and valve tip.

63. Summary (12 of 17)
Camshaft followers are used in overhead camshaft engines in place of rocker arms.
Bucket-style lifts transmit movement from the cam lobe to the tip of the valve.
The valve spring is designed to close the valve and exert pressure to hold it firmly against the valve seat.

64. Summary (13 of 17)
Valve-spring retainers and valve locks (keepers) hold the valve spring in place.
Gaskets are designed to create a seal when compressed between two stationary parts.
Gaskets are single use only and must withstand engine heat.
Functions of a head gasket are to seal and contain combustion pressure, seal oil passages, and control coolant flow.

65. Summary (14 of 17) Anisotropic head gaskets conduct heat laterally.
Oil seals can seal the rotating parts of an engine and are made of rubber or a rubber-type compound comprised of silicone, EPDM, or other flexible material.
The lip-type dynamic oil seal is the most commonly used type.

66. Summary (15 of 17)
O-rings are used to seal stationary or slowly rotating shafts.
Sealants are designed to seal together two surfaces in stationary contact with one another.
Always check manufacturer recommendations for the proper type of sealant.

67. Summary (16 of 17)
Common cylinder head problems include: wear, cracks, leaking coolant or compression gases, warped cylinder head, burnt or warped valves, and stripped spark plug hole threads.
Thermal stress is the main cause of cylinder head cracks.

68. Summary (17 of 17)
Many cylinder head repairs require the skill of a certified machinist.
Only remove the cylinder head after extensive testing and uncertainty that removal is required.
Always clean the cylinder head after removal.
Test valve springs for squareness and measure both spring height and installed pressure.

69. Credits
Unless otherwise indicated, all photographs and illustrations are under copyright of Jones & Bartlett Learning.