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CHAPTER 10
A
U The Valve Train
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O Classroom Manual
M Page 243
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T Lab Manual
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Page 245
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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.
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E Describe the relationship between the
R camshaft lobe design and lift, duration
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and overlap.
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CHAPTER OBJECTIVES
A
U Properly degree a camshaft.
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O Explain the purpose of lifters.
M Describe the operation of hydraulic
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lifters.
I Inspect the pushrods & DNR.
V
E Describe the methods used to correct
R rocker arms, and rocker arm geometry.
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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.
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I Cam grind determines driveability
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characteristics.
R Cam Drives
K Page 243
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CAM DRIVES
A
U The Camshaft is Driven by the
T Crankshaft.
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M Cam is driven at one half Crank speed.
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Cam Gear has twice as many teeth as
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I crank gear.
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K Page 244 Class
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CAM DRIVES
A
U Threetypes of cam drives.
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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
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GEAR DRIVES
A
U Cam gear is soft - Fiber or Aluminum
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Are press fit to cam - Pre-heat to 200
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M degrees to install.
O Crank gear - Steel
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I Advantages - Less wear and Backlash
V Disadvantages - Takes more space and
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R can be noisy.
K Page 245
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SPROCKETS
A
U Used with chains.
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O Can be made of:
M Steel
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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)
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O Silent Chain - 2 styles
M Small Pin - Stiff
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T Large Pin - Limp
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K Page 245
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TIMING BELTS
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U Cogged Belt Drive.
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O Advantages Lighter, Quieter, Easier to
M Change.
O
Virtually no stretch in service.
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I Watch rib tooth shape - Rounded or
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Square.
R Replacement 30,000 to 60,000 miles.
K Page 245
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ECCENTRIC ADJUSTER
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C TIMING the CAM
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C to the CRANK
A
U Timing marks facing each other.
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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
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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
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B CAMSHAFT
C Two cam lobes per cylinder
A
One lobe for the Intake Valve
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T One for the Exhaust Valve
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M High Performance Multi-Valve per
O Cylinder Engines
T
I One lobe per valve 4 on 4 valve per
V cylinder
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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
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distributor shaft.
O Lifters also provide thrust.
T
I Timing Chain.
V Some Engines have a thrust plate.
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K Lecture
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PARTS of a CAM LOBE
A
U Basecircle
T
O Lobe or Nose
M Opening and Closing Ramps
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T Opening and Closing Clearance Ramp
I Page 194 Figure 8.22
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K Page 245
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PARTS of a CAM LOBE
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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
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at TDC.
R Centerline - Point of maximum opening.
K Page 248
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CAM CARD
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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.
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M Asymmetrical - Intake and Exhaust
O Profiles are different.
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K Page 248
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OVERLAP and CENTERLINE
A Lobe spread 105 to 115 degrees.
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T Advanced cam timing - Intake
O centerline less than lobe spread.
M
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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
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K Page 254 Lab
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VALVE LIFTERS
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U Mechanical
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O Hydraulic
M FlatTappet
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T Mushroom
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Roller
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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.
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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.
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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
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instant cam failure.
I Oil changes are important to cam life.
V Page 194 Figure 8.21
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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.
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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
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C AND LIFTERS
A
U I do not recommend using reground
T cams.
O
M I do not recommend using reground
O lifters.
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K Page 259 Lab
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VALVE LASH
A
U Mechanical Camshafts
T
O Hydraulic Camshafts
M Clearance
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K Page 263 Lab