Halderman ch032 lecture

7,719 views

Published on

1 Comment
12 Likes
Statistics
Notes
No Downloads
Views
Total views
7,719
On SlideShare
0
From Embeds
0
Number of Embeds
5,821
Actions
Shares
0
Downloads
18
Comments
1
Likes
12
Embeds 0
No embeds

No notes for slide
  • Figure 32-1 This high-performance camshaft has a lobe that opens the valve quickly and keeps it open for a long time.
  • Figure 32-2 In many engines, the camshaft drives the distributor and the oil pump through a shaft from the end of the distributor.
  • Figure 32-3 The camshaft rides on bearings inside the engine block above the crankshaft on a typical cam-in-block engine.
  • Figure 32-4 Parts of a cam and camshaft terms (nomenclature).
  • Figure 32-5 A composite camshaft is lightweight and yet flexible, because the hollow tube can absorb twisting forces and the lobes are hard enough to withstand the forces involved in opening valves.
  • Figure 32-6 Worn camshaft with two lobes worn to the point of being almost round.
  • Figure 32-7 The fuel pump rocker arm rides on the camshaft eccentric.
  • Figure 32-8 A timing chain hydraulic tensioner.
  • Figure 32-9 The larger camshaft gear is usually made from fiber and given a helical cut to help reduce noise. By making the camshaft gear twice as large as the crankshaft gear, the camshaft rotates one revolution for every two of the crankshaft.
  • Figure 32-10 A replacement silent chain and sprockets. The original camshaft sprocket was aluminum with nylon teeth to help control noise. This replacement set will not be noticeably louder than the original and should give the owner many thousands of miles of useful service.
  • Figure 32-11 The industry standard for when to replace a timing chain and gears is when 1/2 in. (13 mm) or more of slack is measured in the chain. However, it is best to replace the timing chain and gear anytime the camshaft is replaced or the engine is disassembled for repair or overhaul.
  • Figure 32-12 A replacement high-performance double roller chain. Even though a bit noisier than a flat-link chain, a roller chain does not stretch as much and will therefore be able to maintain accurate valve timing for a long time.
  • Figure 32-13 This dual overhead camshaft (DOHC) engine uses one chain from the crankshaft to the intake cam and a secondary chain to rotate the exhaust camshaft.
  • Figure 32-14 A timing belt failed when the teeth were sheared off. This belt failed at 88,000 miles because the owner failed to replace it at the recommended interval of 60,000 miles.
  • Figure 32-15 This timing belt broke because an oil leak from one of the camshaft seals caused oil to get into and weaken the belt. Most experts recommend replacing all engine seals in the front of the engine anytime a timing belt is replaced. If the timing belt travels over the water pump, the water pump should also be replaced as a precaution.
  • Figure 32-16 Many engines are of the interference design. If the timing belt (or chain) breaks, the piston still moves up and down in the cylinder while the valves remain stationary. With a freewheeling design, nothing is damaged, but in an interference engine, the valves are often bent.
  • Figure 32-17 A head from a Mercedes showing bent valves when the timing chain stretched and skipped over the crankshaft sprocket. When this happened, the piston kept moving and bent the valves.
  • Figure 32-18 The slight angle and the curve on the bottom of a flat bottom lifter cause the lifter and the pushrod to rotate during normal operation.
  • Figure 32-19 The lobe lift is the amount the cam lobe lifts the lifter. The blue circle is called the base circle. Because the rocker arm adds to this amount, the entire valve train has to be considered when selecting a camshaft that has the desired lift and duration.
  • Figure 32-20 The ramps on the cam lobe allow the valves to be opened and closed quickly yet under control to avoid damaging valve train components, especially at high engine speeds.
  • Figure 32-21 A 1.5:1 ratio rocker arm means that dimension A is 1.5 times the length of dimension B. Therefore, if the pushrod is moved up 0.4 in. by the camshaft lobe, the valve will be pushed down (opened) 0.4 in. ✕ 1.5, or 0.6 in.
  • Figure 32-22 A high-performance aluminum roller rocker arm. Both the pivot and the tip that contacts the stem of the valve are equipped with rollers to help reduce friction for more power and better fuel economy.
  • Figure 32-23 Some engines today use rocker shafts to support rocker arms such as the V-6 engine with a single overhead camshaft located in the center of the cylinder head.
  • Figure 32-24 A typical stud-mounted rocker arm.
  • Figure 32-25 Pushrod guide plates are bolted to the head and help stabilize the valve train, especially at high engine speeds.
  • Figure 32-26 A pedestal-type rocker arm design that used one bolt for each rocker arm and is nonadjustable. If valve lash needs to be adjusted, different length pushrod(s) must be used.
  • Figure 32-27 Overhead valve engines are also known as pushrod engines because of the long pushrod that extends from the lifter to the rocker arm.
  • Figure 32-28 When the timing chain broke, the valves stopped moving up and down but the pistons kept moving and hit the valves causing the pushrods to bend.
  • Figure 32-30 Hydraulic lifters may be built into bucket-type lifters on some overhead camshaft engines.
  • Figure 32-31 The use of cam followers allows the use of hydraulic lifters with an overhead camshaft design.
  • Figure 32-32 Hydraulic lash adjusters (HLA) are built into the rocker arm on some OHC engines. Sometimes hydraulic lash adjusters may not bleed down properly if the wrong viscosity (SAE rating) oil is used.
  • Figure 32-33 Graphic representation of a typical camshaft showing the relationship between the intake and exhaust valves. The shaded area represents the overlap period of 100 degrees.
  • Figure 32-34 As the lobe center angle decreases, the overlap increases, with no other changes in the lobe profile lift and duration.
  • Figure 32-35 Typical cam timing diagram.
  • Chart 32-1 Changing the lobe separation angle has a major effect on engine operation.
  • Figure 32-36 Typical high-performance camshaft specifications on a straight-line graph. Intake valve duration = 39 + 180 + 71 = 290 degrees. Exhaust valve duration = 7 + 180 + 47 = 234 degrees. Because intake and exhaust valve specifications are different, the camshaft grind is called asymmetrical.
  • Figure 32-37 Typical camshaft valve timing diagram with the same specifications as those shown in Figure 32–36 .
  • Figure 32-38 Older engines used flat-bottom lifters, whereas all engines since the 1990s use roller lifters.
  • Figure 32-39 All roller lifters must use some method to keep the lifter straight and not rotating.
  • Figure 32-40 A cutaway of a flat-bottom solid lifter. Because this type of lifter contains a retaining ring and oil holes, it is sometimes confused with a hydraulic lifter that also contains additional parts. The holes in this lifter are designed to supply oil to the rocker arms through a hollow pushrod.
  • Figure 32- 41 An exploded view of a hydraulic roller lifter.
  • Figure 32-42 The cause of a misfire diagnostic trouble code was discovered to be a pushrod that had worn through the rocker arm on a General Motors 3.1 liter V-6 engine.
  • Figure 32-43 Shaft-mounted rocker arms are held in position by an assortment of springs, spacers, and washers, which should be removed so that the entire shaft can be inspected for wear.
  • Figure 32-44 A dial indicator being used to measure cam lobe height.
  • Chart 32-2 A comparison showing the effects of valve timing and lift on engine performance.
  • Chart 32-3 The purpose for varying the cam timing includes providing for more engine torque and power over a wide engine speed and load range.
  • Figure 32-45 Camshaft rotation during advance and retard.
  • Figure 32-46 The camshaft is rotated in relation to the crankshaft by the PCM to provide changes in valve timing.
  • Chart 32-4 Changing the exhaust cam timing mainly helps reduce exhaust emissions, whereas changing the intake cam timing mainly helps the engine produce increased power and torque.
  • Figure 32-47 Spline cam phaser assembly
  • Figure 32-48 A spline phaser.
  • Figure 32-50 A vane phaser is used to move the camshaft, using changes in oil pressure from the oil control valve.
  • Figure 32-51 A magnetically controlled vane phaser.
  • Figure 32-52 A camshaft position actuator used in a cam-in-block engine.
  • Figure 32-53 A plastic mockup of a Honda VTEC system that uses two different camshaft profiles—one for low-speed engine operation and the other for high speed.
  • Figure 32-54 Engine oil pressure is used to switch cam lobes on a VTEC system.
  • Figure 32-55 Oil pressure applied to the locking pin causes the inside of the lifter to freely move inside the outer shell of the lifter, thereby keeping the valve closed.
  • Figure 32-56 Active fuel management includes many different components and changes to the oiling system, which makes routine oil changes even more important on engines equipped with this system.
  • Halderman ch032 lecture

    1. 1. CAMSHAFTS AND VALVE TRAINS 32
    2. 2. Objectives <ul><li>The student should be able to: </li></ul><ul><ul><li>Prepare for the ASE Engine Repair (A1) certification test content area “B” (Cylinder Head and Valve Train Diagnosis and Repair). </li></ul></ul><ul><ul><li>Describe how the camshaft and valve train function </li></ul></ul>
    3. 3. Objectives <ul><li>The student should be able to: </li></ul><ul><ul><li>Discuss valve train noise and its causes. </li></ul></ul><ul><ul><li>Explain how a hydraulic lifter works. </li></ul></ul><ul><ul><li>Describe the purpose and function of variable valve timing. </li></ul></ul>
    4. 4. CAMSHAFT
    5. 5. Camshaft <ul><li>Purpose and Function </li></ul><ul><ul><li>Major function is to open the valves </li></ul></ul><ul><ul><li>Lobes open the valve against the force of the valve springs </li></ul></ul>
    6. 6. Camshaft <ul><li>Operation </li></ul><ul><ul><li>The camshaft is driven by: </li></ul></ul><ul><ul><ul><li>Timing gears </li></ul></ul></ul><ul><ul><ul><li>Timing chains </li></ul></ul></ul><ul><ul><ul><li>Timing belts </li></ul></ul></ul>
    7. 7. Camshaft <ul><li>Operation </li></ul><ul><ul><li>The camshaft may operate the following: </li></ul></ul><ul><ul><ul><li>Mechanical fuel pump (carburetor-equipped engines) </li></ul></ul></ul><ul><ul><ul><li>Oil pump </li></ul></ul></ul><ul><ul><ul><li>Distributor (if equipped) </li></ul></ul></ul>
    8. 8. Figure 32-1 This high-performance camshaft has a lobe that opens the valve quickly and keeps it open for a long time.
    9. 9. Figure 32-2 In many engines, the camshaft drives the distributor and the oil pump through a shaft from the end of the distributor.
    10. 10. Camshaft <ul><li>Camshaft Location </li></ul><ul><ul><li>In the engine block (cam-in-block design) </li></ul></ul><ul><ul><ul><li>Engines called overhead valve (OV) engines </li></ul></ul></ul>
    11. 11. Camshaft <ul><li>Camshaft Location </li></ul><ul><ul><li>Overhead (overhead camshaft (OHC) design) </li></ul></ul><ul><ul><ul><li>Single overhead camshaft (SOHC) design if there is a single overhead camshaft for each bank of cylinders </li></ul></ul></ul>
    12. 12. Figure 32-3 The camshaft rides on bearings inside the engine block above the crankshaft on a typical cam-in-block engine.
    13. 13. CAMSHAFT DESIGN
    14. 14. Camshaft Design <ul><li>Construction </li></ul><ul><ul><li>Lobes </li></ul></ul><ul><ul><li>Bearing journals </li></ul></ul><ul><ul><li>Accessory drive gear </li></ul></ul>
    15. 15. Camshaft Design <ul><li>Construction </li></ul><ul><ul><li>Forged steel (often used in diesel engines) </li></ul></ul><ul><ul><li>Steel machined from a solid billet </li></ul></ul><ul><ul><li>Composite camshafts </li></ul></ul>
    16. 16. Figure 32-4 Parts of a cam and camshaft terms (nomenclature).
    17. 17. Figure 32-5 A composite camshaft is lightweight and yet flexible, because the hollow tube can absorb twisting forces and the lobes are hard enough to withstand the forces involved in opening valves.
    18. 18. Camshaft Design <ul><li>Camshaft Bearing Journals </li></ul><ul><ul><li>Must be larger than the cam lobe on pushrod engines so that the camshaft can be installed in the engine through the cam bearings </li></ul></ul>
    19. 19. Camshaft Design <ul><li>Camshaft Bearing Journals </li></ul><ul><ul><li>Progressively smaller from the front journal to the rear </li></ul></ul><ul><ul><li>Some engines use the same size camshaft bearing on all journals </li></ul></ul>
    20. 20. Camshaft Design <ul><li>Hardness </li></ul><ul><ul><li>Hardness makes a camshaft susceptible to chipping from edge loading or careless handling </li></ul></ul><ul><ul><li>Cast-iron camshafts have about the same hardness throughout </li></ul></ul>
    21. 21. Camshaft Design <ul><li>Hardness </li></ul><ul><ul><li>Steel camshafts are usually constructed from SAE 4160 or 4180 steel and are usually induction hardened </li></ul></ul>
    22. 22. Camshaft Design <ul><li>Hardness </li></ul><ul><ul><li>NOTE: Rockwell is a type of hardness test, and the c represents the scale used. The higher the number, the harder the surface. The abbreviation Rc60, therefore, indicates Rockwell hardness of 60 as measured on the “c” scale. </li></ul></ul>
    23. 23. Figure 32-6 Worn camshaft with two lobes worn to the point of being almost round.
    24. 24. Camshaft Design <ul><li>Camshaft Lubrication </li></ul><ul><ul><li>Cam bearing clearance is critical in engines that transfer lubricating oil from the main oil gallery to the crankshaft around the camshaft journal or the outside of the camshaft bearing </li></ul></ul>
    25. 25. Camshaft Design <ul><li>Camshaft Lubrication </li></ul><ul><ul><li>If the clearance is too great, oil will leak out and the crankshaft bearings will not get enough oil </li></ul></ul>
    26. 26. Camshaft Design <ul><li>Fuel Pump Eccentrics </li></ul><ul><ul><li>Eccentric cam lobe for the mechanical fuel pump is often cast as part of the camshaft used in older engines before fuel injection </li></ul></ul>
    27. 27. Figure 32-7 The fuel pump rocker arm rides on the camshaft eccentric.
    28. 28. CAMSHAFT DRIVES
    29. 29. Camshaft Drives <ul><li>Purpose and Function </li></ul><ul><ul><li>The crankshaft drives the camshaft with: </li></ul></ul><ul><ul><ul><li>Timing gears </li></ul></ul></ul><ul><ul><ul><li>Sprockets and chains </li></ul></ul></ul><ul><ul><ul><li>Sprockets and timing belts </li></ul></ul></ul>
    30. 30. Figure 32-8 A timing chain hydraulic tensioner.
    31. 31. Camshaft Drives <ul><li>Camshaft Chain Drives </li></ul><ul><ul><li>Two types of timing chains are used </li></ul></ul><ul><ul><ul><li>Silent chain type (also known as flat-link or Morse type) </li></ul></ul></ul>
    32. 32. Camshaft Drives <ul><li>Camshaft Chain Drives </li></ul><ul><ul><li>Two types of timing chains are used </li></ul></ul><ul><ul><ul><li>Roller chain type double roller chain </li></ul></ul></ul>
    33. 33. Camshaft Drives <ul><li>Camshaft Chain Drives </li></ul><ul><ul><li>NOTE: When the timing chain stretches, the valve timing will be retarded and the engine will lack low-speed power. In some instances, the chain can wear through the timing chain cover and create an oil leak. </li></ul></ul>
    34. 34. Figure 32-9 The larger camshaft gear is usually made from fiber and given a helical cut to help reduce noise. By making the camshaft gear twice as large as the crankshaft gear, the camshaft rotates one revolution for every two of the crankshaft.
    35. 35. Figure 32-10 A replacement silent chain and sprockets. The original camshaft sprocket was aluminum with nylon teeth to help control noise. This replacement set will not be noticeably louder than the original and should give the owner many thousands of miles of useful service.
    36. 36. Figure 32-11 The industry standard for when to replace a timing chain and gears is when 1/2 in. (13 mm) or more of slack is measured in the chain. However, it is best to replace the timing chain and gear anytime the camshaft is replaced or the engine is disassembled for repair or overhaul.
    37. 37. Figure 32-12 A replacement high-performance double roller chain. Even though a bit noisier than a flat-link chain, a roller chain does not stretch as much and will therefore be able to maintain accurate valve timing for a long time.
    38. 38. Figure 32-13 This dual overhead camshaft (DOHC) engine uses one chain from the crankshaft to the intake cam and a secondary chain to rotate the exhaust camshaft.
    39. 39. Camshaft Drives <ul><li>Camshaft Belt Drives </li></ul><ul><ul><li>Made from rubber and fabric and often reinforced with fiberglass or Kevlar </li></ul></ul><ul><ul><li>Sprocket teeth are square-cut or cogged </li></ul></ul>
    40. 40. Camshaft Drives <ul><li>Camshaft Belt Drives </li></ul><ul><ul><li>Reduce weight compared to a chain drive </li></ul></ul>
    41. 41. Camshaft Drives <ul><li>Camshaft Belt Drives </li></ul><ul><ul><li>Requires no lubrication with reduced noise </li></ul></ul><ul><ul><li>Requires periodic replacement every 60,000 miles (100,000 km) </li></ul></ul>
    42. 42. Camshaft Drives <ul><li>Camshaft Belt Drives </li></ul><ul><ul><li>Freewheeling engines cause no internal damage if the camshaft drive belt breaks when the engine is running </li></ul></ul>
    43. 43. Camshaft Drives <ul><li>Camshaft Belt Drives </li></ul><ul><ul><li>Interference engines cause some of the valves that are open to hit the pistons, causing major engine damage </li></ul></ul>
    44. 44. Figure 32-14 A timing belt failed when the teeth were sheared off. This belt failed at 88,000 miles because the owner failed to replace it at the recommended interval of 60,000 miles.
    45. 45. Figure 32-15 This timing belt broke because an oil leak from one of the camshaft seals caused oil to get into and weaken the belt. Most experts recommend replacing all engine seals in the front of the engine anytime a timing belt is replaced. If the timing belt travels over the water pump, the water pump should also be replaced as a precaution.
    46. 46. Figure 32-16 Many engines are of the interference design. If the timing belt (or chain) breaks, the piston still moves up and down in the cylinder while the valves remain stationary. With a freewheeling design, nothing is damaged, but in an interference engine, the valves are often bent.
    47. 47. Figure 32-17 A head from a Mercedes showing bent valves when the timing chain stretched and skipped over the crankshaft sprocket. When this happened, the piston kept moving and bent the valves.
    48. 48. CAMSHAFT MOVEMENT
    49. 49. Camshaft Movement <ul><li>Reasons Camshafts Move </li></ul><ul><ul><li>Cam chucking is the movement of the camshaft lengthwise in the engine during operation </li></ul></ul>
    50. 50. Camshaft Movement <ul><li>Reasons Camshafts Move </li></ul><ul><ul><li>Camshaft must have some means to control the shaft end thrust </li></ul></ul>
    51. 51. Camshaft Movement <ul><li>Reasons Camshafts Move </li></ul><ul><ul><li>Thrust plates can be placed between the camshaft drive gear or sprocket and a flange to limit forward motion of the camshaft </li></ul></ul>
    52. 52. Camshaft Movement <ul><li>Why Flat-Bottom Lifters Rotate </li></ul><ul><ul><li>Lifter face surface is slightly convex, by about 0.002 in. </li></ul></ul><ul><ul><li>Lifter contacts the lobe at a point that is slightly off center producing a turning force on the lifter to cause some rotation for even wear </li></ul></ul>
    53. 53. Figure 32-18 The slight angle and the curve on the bottom of a flat bottom lifter cause the lifter and the pushrod to rotate during normal operation.
    54. 54. Camshaft Movement <ul><li>Camshaft Lobe Lift </li></ul><ul><ul><li>Expressed in decimal inches </li></ul></ul><ul><ul><li>Represents the distance that the valve lifter or follower is moved </li></ul></ul>
    55. 55. Camshaft Movement <ul><li>Camshaft Lobe Lift </li></ul><ul><ul><li>The amount that the valve is lifted is determined by the lobe lift times the ratio of the rocker arm </li></ul></ul>
    56. 56. Camshaft Movement <ul><li>Camshaft Lobe Lift </li></ul><ul><ul><li>Higher lifts of the camshaft lobe, allow greater amounts of air and fuel to enter the engine increasing the engine's power potential </li></ul></ul>
    57. 57. Camshaft Movement <ul><li>Camshaft Lobe Lift </li></ul><ul><ul><li>Lift of a camshaft is often different for the intake and exhaust valves </li></ul></ul><ul><ul><ul><li>If specifications vary, the camshaft is called asymmetrical </li></ul></ul></ul>
    58. 58. Camshaft Movement <ul><li>Camshaft Lobe Lift </li></ul><ul><ul><li>Lift of a camshaft is often different for the intake and exhaust valves </li></ul></ul><ul><ul><ul><li>If the lift is the same, the cam is called symmetrical </li></ul></ul></ul>
    59. 59. Figure 32-19 The lobe lift is the amount the cam lobe lifts the lifter. The blue circle is called the base circle. Because the rocker arm adds to this amount, the entire valve train has to be considered when selecting a camshaft that has the desired lift and duration.
    60. 60. Figure 32-20 The ramps on the cam lobe allow the valves to be opened and closed quickly yet under control to avoid damaging valve train components, especially at high engine speeds.
    61. 61. ROCKER ARMS
    62. 62. Rocker Arms <ul><li>Purpose and Function </li></ul><ul><ul><li>Reverses the upward movement of the pushrod to produce a downward movement on the tip of the valve </li></ul></ul>
    63. 63. Rocker Arms <ul><li>Purpose and Function </li></ul><ul><ul><li>Designed to reduce the travel of the cam follower or lifter and pushrod while maintaining the required valve lift </li></ul></ul>
    64. 64. Rocker Arms <ul><li>Purpose and Function </li></ul><ul><ul><li>Rocker arms may be: </li></ul></ul><ul><ul><ul><li>Cast </li></ul></ul></ul><ul><ul><ul><li>Forged </li></ul></ul></ul><ul><ul><ul><li>Stamped steel </li></ul></ul></ul>
    65. 65. Rocker Arms <ul><li>Purpose and Function </li></ul><ul><ul><li>CAUTION: Using rocker arms with a higher ratio than stock can also cause the valve spring to compress too much and actually bind. Valve spring bind (coil bind) occurs when the valve spring is compressed to the point where there is no clearance in the spring. (It is completely compressed.) When coil bind occurs in a running engine, bent pushrods, broken rocker arms, or other valve train damage can result. </li></ul></ul>?
    66. 66. Figure 32-21 A 1.5:1 ratio rocker arm means that dimension A is 1.5 times the length of dimension B. Therefore, if the pushrod is moved up 0.4 in. by the camshaft lobe, the valve will be pushed down (opened) 0.4 in. ✕ 1.5, or 0.6 in.
    67. 67. Figure 32-22 A high-performance aluminum roller rocker arm. Both the pivot and the tip that contacts the stem of the valve are equipped with rollers to help reduce friction for more power and better fuel economy.
    68. 68. Rocker Arms <ul><li>Shaft-Mounted Rocker Arms </li></ul><ul><ul><li>Mounted on a shaft that runs the full length of the cylinder head </li></ul></ul><ul><ul><li>Work well, especially at high engine speeds </li></ul></ul>
    69. 69. Rocker Arms <ul><li>Stud-Mounted Rocker Arms </li></ul><ul><ul><li>Only on overhead valve (OHV) engines </li></ul></ul><ul><ul><li>Each arm is attached to a stud pressed or threaded into the cylinder head </li></ul></ul>
    70. 70. Rocker Arms <ul><li>Pedestal-Mounted Rocker Arms </li></ul><ul><ul><li>Similar to stud-mounted rocker arms but do not use a stud </li></ul></ul><ul><ul><li>Used only in overhead valve engines </li></ul></ul>
    71. 71. Rocker Arms <ul><li>Pedestal-Mounted Rocker Arms </li></ul><ul><ul><li>Two rocker arms are attached to and pivot on a pedestal attached to the cylinder head </li></ul></ul>
    72. 72. Figure 32-23 Some engines today use rocker shafts to support rocker arms such as the V-6 engine with a single overhead camshaft located in the center of the cylinder head.
    73. 73. Figure 32-24 A typical stud-mounted rocker arm.
    74. 74. Figure 32-25 Pushrod guide plates are bolted to the head and help stabilize the valve train, especially at high engine speeds.
    75. 75. Figure 32-26 A pedestal-type rocker arm design that used one bolt for each rocker arm and is nonadjustable. If valve lash needs to be adjusted, different length pushrod(s) must be used.
    76. 76. PUSHRODS
    77. 77. Pushrods <ul><li>Purpose and Function </li></ul><ul><ul><li>Transfers the lifting motion of the valve train from the cam lobe and lifters to the rocker arms </li></ul></ul>
    78. 78. Pushrods <ul><li>Types of Pushrods </li></ul><ul><ul><li>Solid or hollow </li></ul></ul><ul><ul><li>Hollow has passages for oil to lubricate rocker arms </li></ul></ul>
    79. 79. Figure 32-27 Overhead valve engines are also known as pushrod engines because of the long pushrod that extends from the lifter to the rocker arm.
    80. 80. Figure 32-28 When the timing chain broke, the valves stopped moving up and down but the pistons kept moving and hit the valves causing the pushrods to bend.
    81. 81. OVERHEAD CAMSHAFT VALVE TRAINS
    82. 82. Overhead Camshaft Valve Trains <ul><li>Terminology </li></ul><ul><ul><li>Several different types of valve opening designs </li></ul></ul><ul><ul><ul><li>One type opens the valves directly with a bucket </li></ul></ul></ul>
    83. 83. Overhead Camshaft Valve Trains <ul><li>Terminology </li></ul><ul><ul><li>Several different types of valve opening designs </li></ul></ul><ul><ul><ul><li>Second type uses a cam follower, also called a finger follower, that provides an opening ratio similar to that of a rocker arm </li></ul></ul></ul>
    84. 84. Overhead Camshaft Valve Trains <ul><li>Terminology </li></ul><ul><ul><li>Several different types of valve opening designs </li></ul></ul><ul><ul><ul><li>Third type moves the rocker arm directly through a hydraulic lifter </li></ul></ul></ul>
    85. 85. Overhead Camshaft Valve Trains <ul><li>Terminology </li></ul><ul><ul><li>Several different types of valve opening designs </li></ul></ul><ul><ul><ul><li>Fourth type – Hydraulic lash adjusters (HLA) </li></ul></ul></ul>
    86. 86. Figure 32-30 Hydraulic lifters may be built into bucket-type lifters on some overhead camshaft engines.
    87. 87. Figure 32-31 The use of cam followers allows the use of hydraulic lifters with an overhead camshaft design.
    88. 88. Figure 32-32 Hydraulic lash adjusters (HLA) are built into the rocker arm on some OHC engines. Sometimes hydraulic lash adjusters may not bleed down properly if the wrong viscosity (SAE rating) oil is used.
    89. 89. CAMSHAFT SPECIFICATIONS
    90. 90. Camshaft Specifications <ul><li>Duration </li></ul><ul><ul><li>Number of degrees of crankshaft (not camshaft) rotation for which a valve is lifted off the seat </li></ul></ul>
    91. 91. Camshaft Specifications <ul><li>Duration </li></ul><ul><ul><li>Three most commonly used methods to express specification for duration include: </li></ul></ul><ul><ul><ul><li>Duration of valve opening at zero lash (clearance) </li></ul></ul></ul>
    92. 92. Camshaft Specifications <ul><li>Duration </li></ul><ul><ul><li>Three most commonly used methods to express specification for duration include: </li></ul></ul><ul><ul><ul><li>Duration at 0.05 in. lifter (tappet) lift </li></ul></ul></ul><ul><ul><ul><li>SAE camshaft specifications </li></ul></ul></ul>
    93. 93. Camshaft Specifications <ul><li>Duration </li></ul><ul><ul><li>NOTE: Fractions of a degree are commonly expressed in units called minutes (´). Sixty (60) minutes equal one degree (1°). For example, 45’ = 3/4 degree, 30’ = 1/2 degree, and 15’ = 1/4 degree. </li></ul></ul>
    94. 94. Camshaft Specifications <ul><li>Valve Overlap </li></ul><ul><ul><li>The number of degrees of crankshaft rotation during which both intake and exhaust valves are open </li></ul></ul>
    95. 95. Camshaft Specifications <ul><li>Valve Overlap </li></ul><ul><ul><li>Overlap occurs at the beginning of the intake stroke and at the end of the exhaust stroke </li></ul></ul>
    96. 96. Camshaft Specifications <ul><li>Valve Overlap </li></ul><ul><ul><li>A lower amount of overlap results in smoother idle and low-engine speed operation, but it also means that a lower amount of power is available at higher engine speeds </li></ul></ul>
    97. 97. Camshaft Specifications <ul><li>Valve Overlap </li></ul><ul><ul><li>A greater valve overlap causes rougher engine idle, with decreased power at low speeds, but it also means that high-speed power is improved </li></ul></ul>
    98. 98. Figure 32-33 Graphic representation of a typical camshaft showing the relationship between the intake and exhaust valves. The shaded area represents the overlap period of 100 degrees.
    99. 99. Camshaft Specifications <ul><li>Calculating Overlap </li></ul><ul><ul><li>Engine features a camshaft where the intake valve starts to open at 19 degrees before top dead center (BTDC) and the exhaust valve is open until 22 degrees after top dead center (ATDC) </li></ul></ul>
    100. 100. Camshaft Specifications <ul><li>Calculating Overlap </li></ul><ul><ul><li>Total the number of degrees for which the intake valve is open BTDC (19 degrees) and the number of degrees for which the exhaust valve is open ATDC (22 degrees): </li></ul></ul><ul><ul><ul><li>Valve overlap = 19 + 22 = 41 degrees </li></ul></ul></ul>
    101. 101. Camshaft Specifications <ul><li>Lobe Centers </li></ul><ul><ul><li>Separation between the centerlines of the intake and exhaust lobes is called: </li></ul></ul><ul><ul><ul><li>Lobe center </li></ul></ul></ul><ul><ul><ul><li>Lobe separation </li></ul></ul></ul>
    102. 102. Camshaft Specifications <ul><li>Lobe Centers </li></ul><ul><ul><li>Separation between the centerlines of the intake and exhaust lobes is called: </li></ul></ul><ul><ul><ul><li>Lobe displacement angle (LDA) </li></ul></ul></ul><ul><ul><ul><li>Lobe spread </li></ul></ul></ul>
    103. 103. Camshaft Specifications <ul><li>Lobe Centers </li></ul><ul><ul><li>Lobe center’s measurement is measured in degrees </li></ul></ul><ul><ul><li>The smaller the angle between the lobe centerlines, the greater the amount of overlap </li></ul></ul>
    104. 104. Camshaft Specifications <ul><li>Lobe Centers </li></ul><ul><ul><li>The larger the angle between the lobe centerlines, the less the amount of overlap </li></ul></ul>
    105. 105. Camshaft Specifications <ul><li>Lobe Centers </li></ul><ul><ul><li>To find the degree of separation between intake and exhaust lobes of a cam, use the following formula: </li></ul></ul><ul><li>(Intake duration+Exhaust duration) − Overlap </li></ul><ul><ul><li>= Number of degrees of separation </li></ul></ul>4 2
    106. 106. Camshaft Specifications <ul><li>Lobe Centers </li></ul><ul><ul><li>NOTE: Some engines that are equipped with dual overhead camshafts and four valves per cylinder use a different camshaft profile for each of the intake and exhaust valves. For example, one intake valve for each cylinder could have a cam profile designed for maximum low-speed torque. </li></ul></ul>
    107. 107. Camshaft Specifications <ul><li>Lobe Centers </li></ul><ul><ul><li>NOTE: The other intake valve for each cylinder could be designed for higher engine speed power. This results in an engine that is able to produce a high torque over a broad engine speed range. </li></ul></ul>
    108. 108. Figure 32-34 As the lobe center angle decreases, the overlap increases, with no other changes in the lobe profile lift and duration.
    109. 109. Figure 32-35 Typical cam timing diagram.
    110. 110. Camshaft Specifications <ul><li>Effects of Lobe Separation on Valve Operation </li></ul><ul><ul><li>A change in lobe separation angle (LSA) has effects engine operation </li></ul></ul>
    111. 111. Chart 32-1 Changing the lobe separation angle has a major effect on engine operation.
    112. 112. Camshaft Specifications <ul><li>Cam Timing Specification </li></ul><ul><ul><li>Stated in terms of the angle of the crankshaft in relation to top dead center (TDC) or bottom dead center (BDC) when the valves open and close </li></ul></ul>
    113. 113. Camshaft Specifications <ul><li>Cam Timing Specification </li></ul><ul><ul><li>The intake valves should open slightly before the piston reaches TDC and starts down on the intake stroke </li></ul></ul>
    114. 114. Camshaft Specifications <ul><li>Cam Timing Specification </li></ul><ul><ul><li>The exhaust valve opens while the piston is traveling down on the power stroke, before the piston starts up on the exhaust stroke </li></ul></ul>
    115. 115. Camshaft Specifications <ul><li>Cam Timing Chart </li></ul><ul><ul><li>Camshaft specifications are given in crankshaft degrees </li></ul></ul><ul><ul><li>The usual method of drawing a camshaft timing diagram is in a circle illustrating two revolutions (720 degrees) of the crankshaft </li></ul></ul>
    116. 116. Figure 32-36 Typical high-performance camshaft specifications on a straight-line graph. Intake valve duration = 39 + 180 + 71 = 290 degrees. Exhaust valve duration = 7 + 180 + 47 = 234 degrees. Because intake and exhaust valve specifications are different, the camshaft grind is called asymmetrical.
    117. 117. Figure 32-37 Typical camshaft valve timing diagram with the same specifications as those shown in Figure 32–36 .
    118. 118. LIFTERS OR TAPPETS
    119. 119. Lifters or Tappets <ul><li>Purpose and Function </li></ul><ul><ul><li>Valve lifters or tappets have the same contour (shape) as the camshaft lobe, which changes the rotary cam motion to a reciprocating motion in the valve train </li></ul></ul>
    120. 120. Lifters or Tappets <ul><li>Purpose and Function </li></ul><ul><ul><li>Lifters are designed with a roller to follow the cam contour </li></ul></ul><ul><ul><li>Roller lifters used primarily in production engines to reduce valve train friction (by up to 8%), which can increase fuel economy </li></ul></ul>
    121. 121. Lifters or Tappets <ul><li>Purpose and Function </li></ul><ul><ul><li>Roller lifters must use a retainer or a guide plate to prevent lifter rotation </li></ul></ul>
    122. 122. Figure 32-38 Older engines used flat-bottom lifters, whereas all engines since the 1990s use roller lifters.
    123. 123. Figure 32-39 All roller lifters must use some method to keep the lifter straight and not rotating.
    124. 124. Lifters or Tappets <ul><li>Valve Lash </li></ul><ul><ul><li>Also called valve train clearance </li></ul></ul><ul><ul><li>Excessive clearance will cause noise or premature failure </li></ul></ul>
    125. 125. Lifters or Tappets <ul><li>Valve Lash </li></ul><ul><ul><li>Two methods of making valve clearance adjustments: </li></ul></ul><ul><ul><ul><li>Solid valve lifter adjusted mechanically at the rocker arm or by changing shims on certain overhead camshaft engines </li></ul></ul></ul>
    126. 126. Lifters or Tappets <ul><li>Valve Lash </li></ul><ul><ul><li>Two methods of making valve clearance adjustments: </li></ul></ul><ul><ul><ul><li>Hydraulic valve lifter has an automatic hydraulic adjustment built into the lifter body </li></ul></ul></ul>
    127. 127. Lifters or Tappets <ul><li>Solid Lifters </li></ul><ul><ul><li>Valve trains using solid lifters must run with some clearance to ensure positive valve closure </li></ul></ul>
    128. 128. Lifters or Tappets <ul><li>Solid Lifters </li></ul><ul><ul><li>Clearance is matched by a gradual rise in the cam contour, called a ramp (Hydraulic lifter camshafts do not have this ramp.) </li></ul></ul><ul><ul><li>Transfers motion directly from the cam to the pushrod or valve </li></ul></ul>
    129. 129. Lifters or Tappets <ul><li>Solid Lifters </li></ul><ul><ul><li>Lightweight cylinder, either hollow or with a small-diameter center section and full-diameter ends </li></ul></ul>
    130. 130. Figure 32-40 A cutaway of a flat-bottom solid lifter. Because this type of lifter contains a retaining ring and oil holes, it is sometimes confused with a hydraulic lifter that also contains additional parts. The holes in this lifter are designed to supply oil to the rocker arms through a hollow pushrod.
    131. 131. Lifters or Tappets <ul><li>Hydraulic Lifters </li></ul><ul><ul><li>Components: </li></ul></ul><ul><ul><ul><li>Hollow cylinder body </li></ul></ul></ul><ul><ul><ul><li>Check valve </li></ul></ul></ul><ul><ul><ul><li>Check ball </li></ul></ul></ul>
    132. 132. Lifters or Tappets <ul><li>Hydraulic Lifters </li></ul><ul><ul><li>Components: </li></ul></ul><ul><ul><ul><li>Plunger </li></ul></ul></ul><ul><ul><ul><li>Pushrod cup </li></ul></ul></ul><ul><ul><ul><li>Locking ring </li></ul></ul></ul>
    133. 133. Lifters or Tappets <ul><li>Hydraulic Lifters </li></ul><ul><ul><li>Leakage allowance designed into the lifter so that the air can bleed out and the lifter can leak down if it should become overfilled </li></ul></ul>
    134. 134. Lifters or Tappets <ul><li>Hydraulic Lifters </li></ul><ul><ul><li>Holes in the pushrod allow oil to transfer from the lifter piston center, past a metering disc or restrictor valve the rocker arm for lubrication </li></ul></ul>
    135. 135. Lifters or Tappets <ul><li>Hydraulic Lifters </li></ul><ul><ul><li>Takes up all clearance in the valve train to keep valve from closing on the seat </li></ul></ul>
    136. 136. Figure 32-41 An exploded view of a hydraulic roller lifter.
    137. 137. VALVE TRAIN LUBRICATION
    138. 138. Valve Train Lubrication <ul><li>Lifters in an overhead valve (OHV) engine lubricated through passages in the block </li></ul><ul><li>Oil flows through the lifter and hollow pushrod to lubricate and cool the rocker arm, valve, and valve spring </li></ul>
    139. 139. Valve Train Lubrication <ul><li>NOTE: The Chrysler 5.7 liter Hemi engine is opposite because the oil is first sent to the rocker arm through passages in the block and head and then down through the hollow pushrod to the lifters. In all other engine designs, the oil flows through the lifter and up to the rocker arm through the hollow pushrod. </li></ul>
    140. 140. Valve Train Lubrication <ul><li>Camshaft Lubrication </li></ul><ul><ul><li>Camshafts in overhead valve (OHV) engines are lubricated by splash oil thrown up by the crankshaft </li></ul></ul>
    141. 141. Valve Train Lubrication <ul><li>Camshaft Lubrication </li></ul><ul><ul><li>Less splash lubrication occurs at lower engine speeds than at higher speeds </li></ul></ul>
    142. 142. Valve Train Lubrication <ul><li>Camshaft Lubrication </li></ul><ul><ul><li>Engines equipped with flat-bottom lifters should be operated at a fast idle of about 2,500 RPM during the first 10 minutes of engine operation </li></ul></ul>
    143. 143. VALVE TRAIN PROBLEM DIAGNOSIS
    144. 144. Valve Train Problem Diagnosis <ul><li>Symptoms </li></ul><ul><ul><li>“ Tick, tick, tick” noise is heard if cam lobe is worn </li></ul></ul><ul><ul><li>Noise can be intermittent </li></ul></ul>
    145. 145. Figure 32-42 The cause of a misfire diagnostic trouble code was discovered to be a pushrod that had worn through the rocker arm on a General Motors 3.1 liter V-6 engine.
    146. 146. Valve Train Problem Diagnosis <ul><li>Valve Noise Diagnosis </li></ul><ul><ul><li>Many manufacturers consider valve ticking at one-half engine speed after start-up to be normal, especially if the engine is quiet after 10 to 30 seconds </li></ul></ul>
    147. 147. Valve Train Problem Diagnosis <ul><li>Valve Noise Diagnosis </li></ul><ul><ul><li>Be sure vehicle is equipped with the correct oil filter, and that it has an internal check valve </li></ul></ul>
    148. 148. Valve Train Problem Diagnosis <ul><li>Valve Noise Diagnosis </li></ul><ul><ul><li>Check oil level if all valves are noisy </li></ul></ul><ul><ul><li>Low oil means it may have been aerated </li></ul></ul>
    149. 149. Valve Train Problem Diagnosis <ul><li>Valve Noise Diagnosis </li></ul><ul><ul><li>Aeration can be caused by: </li></ul></ul><ul><ul><ul><li>Low oil pressure, which can also cause all valves to be noisy </li></ul></ul></ul><ul><ul><ul><li>High oil level, which can also cause noisy valve lifters </li></ul></ul></ul>
    150. 150. Valve Train Problem Diagnosis <ul><li>Valve Noise Diagnosis </li></ul><ul><ul><li>Aeration can be caused by: </li></ul></ul><ul><ul><ul><li>Check all of the following: </li></ul></ul></ul><ul><ul><ul><ul><li>Valve lash too loose </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Worn camshaft lobe </li></ul></ul></ul></ul>
    151. 151. Valve Train Problem Diagnosis <ul><li>Valve Noise Diagnosis </li></ul><ul><ul><li>Aeration can be caused by: </li></ul></ul><ul><ul><ul><li>Check all of the following: </li></ul></ul></ul><ul><ul><ul><ul><li>Dirty, stuck, or worn lifters </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Worn rocker arm (if the vehicle is so equipped) </li></ul></ul></ul></ul>
    152. 152. Valve Train Problem Diagnosis <ul><li>Valve Noise Diagnosis </li></ul><ul><ul><li>Aeration can be caused by: </li></ul></ul><ul><ul><ul><li>Check all of the following: </li></ul></ul></ul><ul><ul><ul><ul><li>Worn rocker arm shaft </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Worn or bent pushrods (if the vehicle is so equipped) </li></ul></ul></ul></ul>
    153. 153. Valve Train Problem Diagnosis <ul><li>Valve Noise Diagnosis </li></ul><ul><ul><li>Aeration can be caused by: </li></ul></ul><ul><ul><ul><li>Check all of the following: </li></ul></ul></ul><ul><ul><ul><ul><li>Broken or weak valve springs </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Sticking or warped valves </li></ul></ul></ul></ul>
    154. 154. Figure 32-43 Shaft-mounted rocker arms are held in position by an assortment of springs, spacers, and washers, which should be removed so that the entire shaft can be inspected for wear.
    155. 155. CAMSHAFT REMOVAL
    156. 156. Camshaft Removal <ul><li>Cam-In Block Engines </li></ul><ul><ul><li>Timing chain and gears should be removed </li></ul></ul><ul><ul><li>Loosen rocker arms (or rocker arm shaft) and remove pushrods </li></ul></ul><ul><ul><li>Remove the valve lifters before removing the camshaft </li></ul></ul>
    157. 157. Camshaft Removal <ul><li>Cam-In Block Engines </li></ul><ul><ul><li>NOTE: Be sure to keep the pushrods and rocker arms together if they are to be reused. </li></ul></ul>
    158. 158. MEASURING CAMSHAFTS
    159. 159. Measuring Camshafts <ul><li>Total Indicator Runout </li></ul><ul><ul><li>Measuring cam bearings for runout using a dial indicator </li></ul></ul><ul><ul><li>Maximum total indicator runout (TIR) (also called total indicated runout) should be less than 0.002 in. (0.05 mm) </li></ul></ul>
    160. 160. Measuring Camshafts <ul><li>Cam Lobe Height </li></ul><ul><ul><li>Measured to verify exact camshaft installed </li></ul></ul><ul><ul><li>Attach a dial indicator and slowly rotate engine </li></ul></ul><ul><ul><li>Compare the indicator reading to factory specifications </li></ul></ul>
    161. 161. Figure 32-44 A dial indicator being used to measure cam lobe height.
    162. 162. SELECTING A CAMSHAFT
    163. 163. Selecting a Camshaft <ul><li>Determining Engine Usage </li></ul><ul><ul><li>In rebuilds, use a camshaft with the same specifications as the engine had from the factory </li></ul></ul>
    164. 164. Selecting a Camshaft <ul><li>Determining Engine Usage </li></ul><ul><ul><li>Many engine builders will want to select a different camshaft than the stock version for more power </li></ul></ul>
    165. 165. Selecting a Camshaft <ul><li>Determining Engine Usage </li></ul><ul><ul><li>Common mistake is to install a camshaft with too much duration for the size of the engine </li></ul></ul>
    166. 166. Selecting a Camshaft <ul><li>Determining Engine Usage </li></ul><ul><ul><li>Check with camshaft manufacturer for the best camshaft to use </li></ul></ul>
    167. 167. Selecting a Camshaft <ul><li>Determining Engine Usage </li></ul><ul><ul><li>Be prepared to give them the following information: </li></ul></ul><ul><ul><ul><li>Engine make and size </li></ul></ul></ul><ul><ul><ul><li>Weight of the vehicle </li></ul></ul></ul>
    168. 168. Selecting a Camshaft <ul><li>Determining Engine Usage </li></ul><ul><ul><li>Be prepared to give them the following information: </li></ul></ul><ul><ul><ul><li>Type of transmission </li></ul></ul></ul><ul><ul><ul><li>Final drive gear ratio </li></ul></ul></ul><ul><ul><ul><li>Intended use of the vehicle </li></ul></ul></ul>
    169. 169. Chart 32-2 A comparison showing the effects of valve timing and lift on engine performance.
    170. 170. VARIABLE VALVE TIMING
    171. 171. Variable Valve Timing <ul><li>Purpose and Function </li></ul><ul><ul><li>Three basic types: </li></ul></ul><ul><ul><ul><li>Exhaust camshaft variable action only on overhead camshaft engines, such as on many inline 4- and 6-cylinder engines </li></ul></ul></ul>
    172. 172. Variable Valve Timing <ul><li>Purpose and Function </li></ul><ul><ul><li>Three basic types: </li></ul></ul><ul><ul><ul><li>Intake and exhaust camshaft variable action on both camshafts used in many engines </li></ul></ul></ul>
    173. 173. Variable Valve Timing <ul><li>Purpose and Function </li></ul><ul><ul><li>Three basic types: </li></ul></ul><ul><ul><ul><li>Changing the relationship of the camshaft to the crankshaft, in overhead valve cam-in-block engines </li></ul></ul></ul>
    174. 174. Variable Valve Timing <ul><li>Purpose and Function </li></ul><ul><ul><li>Used by the following vehicle manufacturers: </li></ul></ul><ul><ul><ul><li>General Motors 4-, 5-, 6-, and 8-cylinder engines </li></ul></ul></ul><ul><ul><ul><li>BMW </li></ul></ul></ul><ul><ul><ul><li>Chrysler </li></ul></ul></ul>
    175. 175. Variable Valve Timing <ul><li>Purpose and Function </li></ul><ul><ul><li>Used by the following vehicle manufacturers: </li></ul></ul><ul><ul><ul><li>Ford </li></ul></ul></ul><ul><ul><ul><li>Nissan/Infinity </li></ul></ul></ul><ul><ul><ul><li>Toyota/Lexus </li></ul></ul></ul>
    176. 176. Chart 32-3 The purpose for varying the cam timing includes providing for more engine torque and power over a wide engine speed and load range.
    177. 177. Variable Valve Timing <ul><li>Operation </li></ul><ul><ul><li>Camshaft position actuator (oil control valve (OCV)) directs oil from the oil feed in the head to the appropriate camshaft position actuator oil passages </li></ul></ul>
    178. 178. Figure 32-45 Camshaft rotation during advance and retard.
    179. 179. Variable Valve Timing <ul><li>OHV Variable Timing </li></ul><ul><ul><li>Valve in the intake manifold creates a longer path for intake air at low speeds </li></ul></ul><ul><ul><li>Valve opens and creates a shorter air path at higher speeds </li></ul></ul>
    180. 180. Variable Valve Timing <ul><li>OHV Variable Timing </li></ul><ul><ul><li>Varying the exhaust and/or the intake camshaft position reduces exhaust emissions and improves performance </li></ul></ul>
    181. 181. Variable Valve Timing <ul><li>OHV Variable Timing </li></ul><ul><ul><li>Varying the exhaust cam phasing, enables manufacturers to meet newer NOx reduction standards and eliminate the exhaust gas recirculation (EGR) valve </li></ul></ul>
    182. 182. Variable Valve Timing <ul><li>OHV Variable Timing </li></ul><ul><ul><li>With exhaust cam phasing, the powertrain control module (PCM) can close the exhaust valves sooner than usual </li></ul></ul>
    183. 183. Variable Valve Timing <ul><li>OHV Variable Timing </li></ul><ul><ul><li>Manufacturers use one or two actuators that allow the camshaft piston to change by up to 50 degrees in relation to the crankshaft position </li></ul></ul>
    184. 184. Variable Valve Timing <ul><li>OHV Variable Timing </li></ul><ul><ul><li>The two types of cam phasing devices commonly used are: </li></ul></ul><ul><ul><ul><li>Spline phaser: on overhead camshaft (OHC) engines </li></ul></ul></ul>
    185. 185. Variable Valve Timing <ul><li>OHV Variable Timing </li></ul><ul><ul><li>The two types of cam phasing devices commonly used are: </li></ul></ul><ul><ul><ul><li>Vane phaser: on overhead camshaft (OHC) and overhead valve (OHV) cam-in-block engines </li></ul></ul></ul>
    186. 186. Figure 32-46 The camshaft is rotated in relation to the crankshaft by the PCM to provide changes in valve timing.
    187. 187. Chart 32-4 Changing the exhaust cam timing mainly helps reduce exhaust emissions, whereas changing the intake cam timing mainly helps the engine produce increased power and torque.
    188. 188. Variable Valve Timing <ul><li>Spline Phaser System </li></ul><ul><ul><li>Also called valve cam phaser (VCP) </li></ul></ul><ul><ul><li>Consists of the following components: </li></ul></ul><ul><ul><ul><li>Engine control module (ECM) </li></ul></ul></ul><ul><ul><ul><li>Four-way pulse-width-modulated (PWM) control valve </li></ul></ul></ul>
    189. 189. Variable Valve Timing <ul><li>Spline Phaser System </li></ul><ul><ul><li>Consists of the following components: </li></ul></ul><ul><ul><ul><li>Cam phaser assembly </li></ul></ul></ul><ul><ul><ul><li>Camshaft position (CMP) sensor </li></ul></ul></ul>
    190. 190. Figure 32-47 Spline cam phaser assembly
    191. 191. Variable Valve Timing <ul><li>Spline Phaser System Operation </li></ul><ul><ul><li>Oil pressure regulated by the control valve and directed to ports in the cylinder head leading to the camshaft and cam phaser position </li></ul></ul>
    192. 192. Variable Valve Timing <ul><li>Spline Phaser System Operation </li></ul><ul><ul><li>Piston is moved inside the cam phaser and rides along the helical splines, compressing the coil spring </li></ul></ul>
    193. 193. Variable Valve Timing <ul><li>Spline Phaser System Operation </li></ul><ul><ul><li>Cam phaser gear and the camshaft move in opposite directions retarding the cam timing </li></ul></ul>
    194. 194. Variable Valve Timing <ul><li>Spline Phaser System Operation </li></ul><ul><ul><li>NOTE: A unique cam-within-a-cam is used on 2008 and newer Dodge Viper V-10 OHV engines. This design allows the exhaust lobes to be moved by up to 36 degrees to improve idle quality and reduction of exhaust emissions. </li></ul></ul>
    195. 195. Figure 32-48 A spline phaser.
    196. 196. Variable Valve Timing <ul><li>Vane Phaser System on an Overhead Camshaft Engine </li></ul><ul><ul><li>Uses a camshaft piston (CMP) sensor on each camshaft </li></ul></ul><ul><ul><li>Each camshaft has its own actuator and oil control valve (OCV) </li></ul></ul>
    197. 197. Variable Valve Timing <ul><li>Vane Phaser System on an Overhead Camshaft Engine </li></ul><ul><ul><li>Uses a rotor with four vanes connected to the end of the camshaft </li></ul></ul><ul><ul><li>Oil pressure is controlled on both sides of the vanes of the rotor, creating a hydraulic link between the two parts </li></ul></ul>
    198. 198. Variable Valve Timing <ul><li>Vane Phaser System on an Overhead Camshaft Engine </li></ul><ul><ul><li>Oil control valve varies the balance of pressure on either side of the vanes controlling the position of the camshaft </li></ul></ul>
    199. 199. Figure 32-50 A vane phaser is used to move the camshaft, using changes in oil pressure from the oil control valve.
    200. 200. Variable Valve Timing <ul><li>Magnetically Controlled Vane Phaser </li></ul><ul><ul><li>Controlled by PCM using a 12-volt pulse-width-modulated (PWM) signal to an electromagnet, which operates the oil control valve (OCV) </li></ul></ul>
    201. 201. Variable Valve Timing <ul><li>Magnetically Controlled Vane Phaser </li></ul><ul><ul><li>Used on many double overhead camshaft engines on both the intake and exhaust camshafts </li></ul></ul>
    202. 202. Variable Valve Timing <ul><li>Magnetically Controlled Vane Phaser </li></ul><ul><ul><li>The following occurs with a change in pulse width: </li></ul></ul><ul><ul><ul><li>0% pulse width: oil directed to the advance chamber of the exhaust camshaft actuator and the retard chamber of the intake camshaft activator </li></ul></ul></ul>
    203. 203. Variable Valve Timing <ul><li>Magnetically Controlled Vane Phaser </li></ul><ul><ul><li>The following occurs with a change in pulse width: </li></ul></ul><ul><ul><ul><li>50% pulse width: computer holds camshaft steady in desired position </li></ul></ul></ul>
    204. 204. Variable Valve Timing <ul><li>Magnetically Controlled Vane Phaser </li></ul><ul><ul><li>The following occurs with a change in pulse width: </li></ul></ul><ul><ul><ul><li>100% pulse width: oil directed to the retard chamber of the exhaust camshaft actuator and the advance chamber of the intake camshaft actuator </li></ul></ul></ul>
    205. 205. Variable Valve Timing <ul><li>Magnetically Controlled Vane Phaser </li></ul><ul><ul><li>ECM uses the following sensors to determine best camshaft position: </li></ul></ul><ul><ul><ul><li>Engine speed (RPM) </li></ul></ul></ul><ul><ul><ul><li>MAP sensor </li></ul></ul></ul>
    206. 206. Variable Valve Timing <ul><li>Magnetically Controlled Vane Phaser </li></ul><ul><ul><li>ECM uses the following sensors to determine best camshaft position: </li></ul></ul><ul><ul><ul><li>Crankshaft position (CKP) </li></ul></ul></ul><ul><ul><ul><li>Camshaft position (CMP) </li></ul></ul></ul><ul><ul><ul><li>Barometric pressure (BARO) </li></ul></ul></ul>
    207. 207. Figure 32-51 A magnetically controlled vane phaser.
    208. 208. Variable Valve Timing <ul><li>Cam-In-Block Engine Cam Phaser </li></ul><ul><ul><li>Magnetically controlled </li></ul></ul><ul><ul><li>Varies the camshaft in relation to the crankshaft </li></ul></ul>
    209. 209. Variable Valve Timing <ul><li>Cam-In-Block Engine Cam Phaser </li></ul><ul><ul><li>Not capable of changing the duration of valve opening or valve lift </li></ul></ul><ul><ul><li>Inside actuator is a rotor with vanes attached to the camshaft </li></ul></ul>
    210. 210. Variable Valve Timing <ul><li>Cam-In-Block Engine Cam Phaser </li></ul><ul><ul><li>Oil pressure to vanes causes camshaft rotation in relation to the crankshaft </li></ul></ul>
    211. 211. Variable Valve Timing <ul><li>Cam-In-Block Engine Cam Phaser </li></ul><ul><ul><li>Camshaft actuator solenoid valve directs flow of oil to side vanes of the actuator </li></ul></ul>
    212. 212. Variable Valve Timing <ul><li>Cam-In-Block Engine Cam Phaser </li></ul><ul><ul><li>NOTE: When oil pressure drops to zero when the engine stops, a spring-loaded locking pin is used to keep the camshaft locked to prevent noise at engine start. When the engine starts, oil pressure releases the locking pin. </li></ul></ul>
    213. 213. Figure 32-52 A camshaft position actuator used in a cam-in-block engine.
    214. 214. VARIABLE LIFT AND CYLINDER DEACTIVATION SYSTEMS
    215. 215. Variable Lift and Cylinder Deactivation Systems <ul><li>Variable Valve Lift Systems </li></ul><ul><ul><li>Variable camshafts include the system used by Honda/Acura, called variable valve timing and lift electronic control (VTEC) </li></ul></ul>
    216. 216. Variable Lift and Cylinder Deactivation Systems <ul><li>Variable Valve Lift Systems </li></ul><ul><ul><li>Uses two different camshafts for low and high RPM </li></ul></ul><ul><ul><li>Process of switching from low-speed to high-speed profiles takes about 100 milliseconds (0.1 sec) </li></ul></ul>
    217. 217. Figure 32-53 A plastic mockup of a Honda VTEC system that uses two different camshaft profiles—one for low-speed engine operation and the other for high speed.
    218. 218. Figure 32-54 Engine oil pressure is used to switch cam lobes on a VTEC system.
    219. 219. Variable Lift and Cylinder Deactivation Systems <ul><li>Cylinder Deactivation Systems </li></ul><ul><ul><li>Powertrain control module (PCM) determines when to deactivate cylinders </li></ul></ul><ul><ul><li>Process uses two-stage hydraulic valve lifters </li></ul></ul>
    220. 220. Variable Lift and Cylinder Deactivation Systems <ul><li>Cylinder Deactivation Systems </li></ul><ul><ul><li>Oil pressure keeps the valve closed </li></ul></ul><ul><ul><li>Oil flow is used to activate or deactivate the cylinders </li></ul></ul>
    221. 221. Variable Lift and Cylinder Deactivation Systems <ul><li>Cylinder Deactivation Systems </li></ul><ul><ul><li>General Motors calls this system “active fuel management” </li></ul></ul><ul><ul><li>Chrysler calls this a “multiple displacement system” (MDS) </li></ul></ul>
    222. 222. Figure 32-55 Oil pressure applied to the locking pin causes the inside of the lifter to freely move inside the outer shell of the lifter, thereby keeping the valve closed.
    223. 223. Figure 32-56 Active fuel management includes many different components and changes to the oiling system, which makes routine oil changes even more important on engines equipped with this system.
    224. 224. TECH TIP <ul><li>Best to Warn the Customer </li></ul><ul><ul><li>A technician replaced a timing chain and gears on a high mileage Chevrolet V-8. The repair was accomplished correctly, yet after starting, the engine burned an excessive amount of oil. Before the timing chain replacement, oil consumption was minimal. </li></ul></ul>BACK TO PRESENTATION <ul><li>The replacement timing chain restored proper operation of the engine by restoring the proper cam and valve timing which increased engine vacuum. Increased vacuum can draw oil from the crankcase past worn piston rings and through worn valve guides during the intake stroke. </li></ul><ul><li>Similar increased oil consumption problems occur if a valve job is performed on a high-mileage engine with worn piston rings and/or cylinders. </li></ul><ul><li>To satisfy the owner of the vehicle, the technicians had to disassemble and refinish the cylinders and replace the piston rings. Therefore, all technicians should warn customers that increased oil usage might result from almost any engine repair to a high-mileage engine. </li></ul>
    225. 225. FREQUENTLY ASKED QUESTION <ul><li>Are the Valves Adjustable? </li></ul><ul><ul><li>If the stud has the same diameter for its whole length, the rockers are adjustable and the nut will be the “interference” type (lock-type nut). If the stud has a shoulder of a different diameter, the rockers are nonadjustable and the nut will not have interference threads. </li></ul></ul>? BACK TO PRESENTATION
    226. 226. TECH TIP <ul><li>Rocker Arm Shafts Can Cause Sticking Valves </li></ul><ul><ul><li>As oil oxidizes, it forms a varnish. Varnish buildup is particularly common on hot upper portions of the engine, such as rocker arm shafts. The varnish restricts clean oil from getting into and lubricating the rocker arms. </li></ul></ul>BACK TO PRESENTATION The cam lobe can easily force the valves open, but the valve springs often do not exert enough force to fully close the valves. The result is an engine miss, which may be intermittent. Worn valve guides and/or weak valve springs can also cause occasional rough idle, uneven running, or an engine misfire.
    227. 227. TECH TIP <ul><li>Hollow Pushrod Dirt </li></ul><ul><ul><li>Many engine rebuilders and remanufacturers do not reuse old hollow pushrods. Dirt, carbon, and other debris are difficult to thoroughly clean from inside a hollow pushrod. When an engine is run with used pushrods, the trapped particles can be dislodged and ruin new bearings and other new engine parts. </li></ul></ul>BACK TO PRESENTATION Therefore, for best results, consider purchasing new hollow pushrods instead of trying to clean and reuse the originals.
    228. 228. TECH TIP <ul><li>The Scratch Test </li></ul><ul><ul><li>All pushrods used with guide plates must be hardened on the sides and on the tips. To easily determine if a pushrod is hardened, simply use a sharp pocketknife to scrape the wall of the pushrod. A heat-treated pushrod will not scratch. </li></ul></ul>BACK TO PRESENTATION <ul><ul><li>Figure 32-29 Hardened pushrods should be used in any engine that uses pushrod guides (plates). To determine if the pushrod is hardened, simply try to scratch the side of the pushrod with a pocketknife. </li></ul></ul>
    229. 229. TECH TIP <ul><li>The Rotating Pushrod Test </li></ul><ul><ul><li>To quickly and easily test whether the camshaft is okay, observe if the pushrods are rotating when the engine is running. This test will work on any overhead valve pushrod engine that uses flat-bottom lifters. Due to the slight angle on the cam lobe and lifter offset, the lifter (and pushrod) should rotate whenever the engine is running. </li></ul></ul>BACK TO PRESENTATION To check, simply remove the rocker arm cover and observe the pushrods when the engine is running. If one or more pushrods are not rotating, this camshaft and/or the lifter for that particular valve is worn and needs to be replaced.
    230. 230. REAL WORLD FIX <ul><li>The Noisy Camshaft </li></ul><ul><ul><li>The owner of an overhead cam 4-cylinder engine complained of a noisy engine. After taking the vehicle to several technicians and getting high estimates to replace the camshaft and followers, the owner tried to find a less expensive solution. </li></ul></ul>BACK TO PRESENTATION <ul><li>Finally, another technician replaced the serpentine drive belt on the front of the engine and “cured” the “camshaft” noise for a fraction of the previous estimates. </li></ul><ul><li>Remember, accessory drive belts can often make noises similar to valve or bad bearing types of noises. Many engines have been disassembled and/or overhauled because of a noise that was later determined to be from one of the following: </li></ul><ul><li>Loose or defective accessory drive belt(s) </li></ul><ul><li>Loose torque converter-to-flex plate (drive plate) bolts (nuts) </li></ul><ul><li>Defective mechanical fuel pump (if equipped) </li></ul>
    231. 231. TECH TIP <ul><li>Hot Lifter in 10 Minutes? </li></ul><ul><ul><li>A technician working at a shop discovered a noisy (defective) valve lifter on an older Chevrolet small block V-8. Another technician questioned how long it would take to replace the lifter and was told, “Less than an hour”! (The factory flat rate was much longer than one hour.) </li></ul></ul>BACK TO PRESENTATION Ten minutes later the repair technician handed the questioning technician a hot lifter that had been removed from the engine. The lifter was removed using the following steps. <ul><ul><li>The valve cover was removed. </li></ul></ul><ul><ul><li>The rocker arm and pushrod for the affected valve were removed. </li></ul></ul><ul><ul><li>The distributor was removed. </li></ul></ul><ul><ul><li>A strong magnet was fed through the distributor opening into the valley area of the engine. (If the valve lifter is not mushroomed or does not have varnish deposits, the defective lifter can be lifted up and out of the engine; remember, the technician was working on a new vehicle.) </li></ul></ul><ul><ul><li>A replacement lifter was attached to the magnet and fed down the distributor hole and over the lifter bore. </li></ul></ul><ul><ul><li>The pushrod was used to help guide the lifter into the lifter bore. </li></ul></ul><ul><ul><li>After the lifter preload was adjusted and the valve cover was replaced, the vehicle was returned to the customer in less than one hour. </li></ul></ul>
    232. 232. TECH TIP <ul><li>Check the Screen on the Control Valve If There Are Problems </li></ul><ul><ul><li>If a NOx emission failure at a state inspection occurs or a diagnostic trouble code is set related to the cam timing, remove the control valve and check for a clogged oil screen. </li></ul></ul>BACK TO PRESENTATION A lack of regular oil changes can cause the screen to become clogged, thereby preventing proper operation. A rough idle is a common complaint because the spring may not be able to return the camshaft to the idle position after a long highway trip. <ul><ul><li>Figure 32-49 The screen(s) protect the solenoid valve from dirt and debris that can cause the valve to stick. This fault can set a P0017 diagnostic trouble code (crankshaft position/camshaft position correlation error). </li></ul></ul>

    ×