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                         CHAPTER 10
A
U    The Valve Train
T
O    Classroom Manual
M    Page 243
O
T    Lab Manual
I
     Page 245
V
E
R
K
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          CHAPTER OBJECTIVES
A
U    Explain  the function of the valve train.
T
O    Describe the automatic belt tensioners.
M    List the components of the valve train.
O
T    Explain the purpose & function of the
I     camshaft.
V
E    Describe the relationship between the
R     camshaft lobe design and lift, duration
K
      and overlap.
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          CHAPTER OBJECTIVES
A
U    Properly  degree a camshaft.
T
O    Explain the purpose of lifters.
M    Describe the operation of hydraulic
O
T
      lifters.
I    Inspect the pushrods & DNR.
V
E    Describe the methods used to correct
R     rocker arms, and rocker arm geometry.
K
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      CHAPTER INTRODUCTION
A
U    Internal   combustion engine is a AIR
T     PUMP.
O
M    MORE AIR - MORE POWER.
O
     Cam grind determines Performance.
T
I    Cam grind determines driveability
V
E
      characteristics.
R    Cam Drives
K                                    Page 243
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                         CAM DRIVES
A
U    The Camshaft is Driven by the
T     Crankshaft.
O
M    Cam is driven at one half Crank speed.
O
     Cam Gear has twice as many teeth as
T
I     crank gear.
V
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K                                  Page 244 Class
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                              CAM DRIVES
A
U    Threetypes of cam drives.
T
O    Timing chain and sprockets.
M        Some engines use spacers between
O         sprocket and cam.
T
I    Gear   drives.
V        Heat Aluminum Gears to aid installation.
E
R    Belt   and sprockets.
K                                       Page 244 Class
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    COMMON CAM DRIVES
A
U
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O
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O
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                             GEAR DRIVES
A
U    Cam    gear is soft - Fiber or Aluminum
T
         Are press fit to cam - Pre-heat to 200
O
M         degrees to install.
O    Crank  gear - Steel
T
I    Advantages - Less wear and Backlash
V    Disadvantages - Takes more space and
E
R     can be noisy.
K                                          Page 245
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                            SPROCKETS
A
U    Used with chains.
T
O    Can be made of:
M      Steel
O
       Iron
T
I      Aluminum (Nylon coated teeth) - can stick
V       oil pump relief valve.
E
R      Not use a worn Sprocket with a
     Do
K    New Chain.                 Page 245
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                      TIMING CHAINS
A
U    Roller Chain (bicycle style)
T
O    Silent Chain - 2 styles
M    Small Pin - Stiff
O
T    Large Pin - Limp
I
V
E
R
K                                    Page 245
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                       TIMING BELTS
A
U    Cogged  Belt Drive.
T
O    Advantages Lighter, Quieter, Easier to
M     Change.
O
     Virtually no stretch in service.
T
I    Watch rib tooth shape - Rounded or
V
E
      Square.
R    Replacement 30,000 to 60,000 miles.
K                                  Page 245
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    ECCENTRIC ADJUSTER
A
U
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C                   TIMING the CAM
B
C                     to the CRANK
A
U    Timing  marks facing each other.
T
O    Timing marks a specified number of
M     links apart.
O
     Timing marks aligned with colored
T
I     links on the chain.
V
     Timing marks align with marks on
E
R     head and block.
K                                Page 247 Lab
C                   TIMING the CAM
B
C                     to the CRANK
A
U    Match  old parts to new ones.
T
O    Specifically match keyway and timing
M     mark.
O
     Make sure # 1 piston is at TDC when
T
I     marks are lined up.
V
     Off brands are noted for inaccurate
E
R     timing marks.
K                                 Page 248 Lab
C
B                           CAMSHAFT
C    Two  cam lobes per cylinder
A
     One lobe for the Intake Valve
U
T    One for the Exhaust Valve
O
M    High Performance Multi-Valve per
O     Cylinder Engines
T
I    One lobe per valve 4 on 4 valve per
V     cylinder
E
R    Fuel Pump Eccentric cast-in or bolted on
K    Distributor and Oil Pump Drive Gear
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                         CAM THRUST
A
U    Cam   Gear provides thrust surface.
T    Oil pump driven by bottom of
O
M
      distributor shaft.
O    Lifters also provide thrust.
T
I    Timing Chain.
V    Some Engines have a thrust plate.
E
R
K                                   Lecture
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             PARTS of a CAM LOBE
A
U    Basecircle
T
O    Lobe or Nose
M    Opening and Closing Ramps
O
T    Opening and Closing Clearance Ramp
I               Page 194 Figure 8.22
V
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K                                       Page 245
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    PARTS of a CAM LOBE
A
U
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O
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K                Page 247
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             CAM MEASUREMENTS
A    Lift- Valve & Cam - Measured in inches.
U    Duration - Measured in degrees of crank
T
O     rotation.
M    Overlap - Both intake & exhaust valves
O
T     open.
I    Split Overlap - Both valves open equally
V
E
      at TDC.
R    Centerline - Point of maximum opening.
K                                   Page 248
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    CAM CARD
A
U
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O
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K      Page 243
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                    CAM PATTERNS
A
U    Single pattern - Intake and Exhaust
T     lobes have same Profile.
O
M    Asymmetrical - Intake and Exhaust
O     Profiles are different.
T
I
V
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K                                  Page 248
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    OVERLAP and CENTERLINE
A    Lobe spread 105 to 115 degrees.
U
T    Advanced cam timing - Intake
O     centerline less than lobe spread.
M
O
         Advanced cam timing improves low and
T         mid range Torque.
I    Retarded cam timing - Intake
V
E    centerline greater than lobe spread.
R        Retarded cam timing improves high RPM
K         power.                        Page 248
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    LOBE SEPARATION ANGLE
A
U
T
O
M
O
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K                   Page 254 Lab
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                   VALVE LIFTERS
A
U    Mechanical
T
O    Hydraulic
M    FlatTappet
O
T    Mushroom
I
     Roller
V
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K                          Page 250
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          LIFTER AND CAM LOBE
A
U    Lifter face has Convex Shape.
T
O    Cam Lobe has taper of .0007” to .002”.
M    Lifter must spin to Dissipate Load.
O
T    Lifter’s convex shape prevents Edge
I     Loading.
V
E
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K                                   Page 249
      LIFTER AND CAM LOBE
 Cam    and Lifters become wear mated in
  first few minutes.
 If cam is replaced replace lifters also.
 Used lifters will rapidly wear out a
  new cam.


                                Page 249
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         LIFTER AND CAM LOBE
A
U    Lubrication  and Break-in.
T
O    Cam is lubed by crank spray
M    First 1/2 Hour is Critical.
O
T    Must use (EP) Extreme Pressure
I     Lubricant.
V
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K                                 Page 249
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          LIFTER AND CAM LOBE
A
U    Minimum    RPM 1500 for 15 Minutes.
T
O    Some OHV have oil passage in cam.
M    Oil holes on each Lobe, if plugged
O
T
      instant cam failure.
I    Oil changes are important to cam life.
V             Page 194 Figure 8.21
E
R
K                                     Page 249
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    ROLLER CAM AND LIFTERS
A
U    Roller lifters can accept higher lift rate
T     without wear.
O
M    Roller lifters reduce valve train friction.
O
     Roller lifters must have a
T
I     way of keeping them from
V
E     turning.
R
K                 Page 250
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    ROLLER CAM AND LIFTERS
A
U    Roller   Cams are made of steel (not cast
T     iron).
O
M    Roller Cams have more aggressive
O     Profiles.
T
I    Lobes are polished to a fine matte
V     finish.
E
R    After break-in, the lobe has a mirror
K     finish.                        Page 245
C              REGRINDING CAMS
B
C                  AND LIFTERS
A
U   I  do not recommend using reground
T     cams.
O
M    I do not recommend using reground
O     lifters.
T
I
V
E
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K                                Page 259 Lab
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                       VALVE LASH
A
U    Mechanical Camshafts
T
O    Hydraulic Camshafts
M    Clearance
O
T
I
V
E
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K                            Page 263 Lab

				
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posted:11/25/2011
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