CHAPTER 10 u The Valve Train u Classroom Manual u Page 243 u Lab Manual u Page 245...

CHAPTER 10

The Valve Train Classroom Manual Page 243 Lab Manual Page 245

CBCAUTOMOTIVERK

CHAPTER OBJECTIVES

Explain the function of the valve train. Describe the automatic belt tensioners. List the components of the valve train. Explain the purpose & function of the

camshaft. Describe the relationship between the

camshaft lobe design and lift, duration and overlap.

CBCAUTOMOTIVERK

CHAPTER OBJECTIVES

Properly degree a camshaft. Explain the purpose of lifters. Describe the operation of hydraulic

lifters. Inspect the pushrods & DNR. Describe the methods used to

correct rocker arms, and rocker arm geometry.

CBCAUTOMOTIVERK

CHAPTER INTRODUCTION

Internal combustion engine is a AIR PUMP.

MORE AIR - MORE POWER. Cam grind determines

Performance. Cam grind determines

driveability characteristics. Cam Drives

CBCAUTOMOTIVERK Page 243

CAM DRIVES

The Camshaft is Driven by the Crankshaft.

Cam is driven at one half Crank speed.

Cam Gear has twice as many teeth as crank gear.

CBCAUTOMOTIVERK Page 244 Class

CAM DRIVES

Three types of cam drives. Timing chain and sprockets.

Some engines use spacers between sprocket and cam.

Gear drives. Heat Aluminum Gears to aid

installation. Belt and sprockets.

CBCAUTOMOTIVERK Page 244 Class

COMMON CAM DRIVESCBCAUTOMOTIVERK

GEAR DRIVES

Cam gear is soft - Fiber or Aluminum Are press fit to cam - Pre-heat to 200

degrees to install. Crank gear - Steel Advantages - Less wear and

Backlash Disadvantages - Takes more space

and can be noisy.


SPROCKETS

Used with chains. Can be made of:

Steel Iron Aluminum (Nylon coated teeth) - can

stick oil pump relief valve. Do Not use a worn Sprocket

with a New Chain.


TIMING CHAINS

Roller Chain (bicycle style) Silent Chain - 2 styles Small Pin - Stiff Large Pin - Limp


TIMING BELTS

Cogged Belt Drive. Advantages Lighter, Quieter,

Easier to Change. Virtually no stretch in service. Watch rib tooth shape -

Rounded or Square. Replacement 30,000 to 60,000

miles.


ECCENTRIC ADJUSTERCBCAUTOMOTIVERK

TIMING the CAMto the CRANK

Timing marks facing each other.

Timing marks a specified number of links apart.

Timing marks aligned with colored links on the chain.

Timing marks align with marks on head and block.

CBCAUTOMOTIVERK Page 247 Lab

TIMING the CAMto the CRANK

Match old parts to new ones. Specifically match keyway and

timing mark. Make sure # 1 piston is at TDC

when marks are lined up. Off brands are noted for

inaccurate timing marks.


CAMSHAFT Two cam lobes per cylinder One lobe for the Intake Valve One for the Exhaust Valve High Performance Multi-Valve per

Cylinder Engines One lobe per valve 4 on 4 valve per

cylinder Fuel Pump Eccentric cast-in or bolted

on Distributor and Oil Pump Drive Gear

CBCAUTOMOTIVERK

CAM THRUST Cam Gear provides thrust

surface. Oil pump driven by bottom of

distributor shaft. Lifters also provide thrust. Timing Chain. Some Engines have a thrust

plate.

CBCAUTOMOTIVERK Lecture

PARTS of a CAM LOBE

Base circle Lobe or Nose Opening and Closing Ramps Opening and Closing Clearance

Ramp Page 194 Figure 8.22


PARTS of a CAM LOBECBCAUTOMOTIVERK Page 247

CAM MEASUREMENTS Lift - Valve & Cam - Measured in inches. Duration - Measured in degrees of crank

rotation. Overlap - Both intake & exhaust valves

open. Split Overlap - Both valves open equally

at TDC. Centerline - Point of maximum opening.


CAM CARD

Page 243

CBCAUTOMOTIVERK

CAM PATTERNS

Single pattern - Intake and Exhaust lobes have same Profile.

Asymmetrical - Intake and Exhaust Profiles are different.


OVERLAP and CENTERLINE Lobe spread 105 to 115 degrees. Advanced cam timing - Intake

centerline less than lobe spread. Advanced cam timing improves low and

mid range Torque. Retarded cam timing - Intake

centerline greater than lobe spread. Retarded cam timing improves high

RPM power.


LOBE SEPARATION ANGLECBCAUTOMOTIVERK Page 254 Lab

VALVE LIFTERS

Mechanical Hydraulic Flat Tappet Mushroom Roller


LIFTER AND CAM LOBE

Lifter face has Convex Shape. Cam Lobe has taper of .0007”

to .002”. Lifter must spin to Dissipate

Load. Lifter’s convex shape prevents

Edge Loading.


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

LIFTER AND CAM LOBE

Lubrication and Break-in. Cam is lubed by crank spray First 1/2 Hour is Critical. Must use (EP) Extreme

Pressure Lubricant.


LIFTER AND CAM LOBE

Minimum RPM 1500 for 15 Minutes.

Some OHV have oil passage in cam.

Oil holes on each Lobe, if plugged instant cam failure.

Oil changes are important to cam life.

Page 194 Figure 8.21


ROLLER CAM AND LIFTERS

Roller lifters can accept higher lift rate without wear.

Roller lifters reduce valve train friction.

Roller lifters must have away of keeping them fromturning.


ROLLER CAM AND LIFTERS

Roller Cams are made of steel (not cast iron).

Roller Cams have more aggressive Profiles.

Lobes are polished to a fine matte finish.

After break-in, the lobe has a mirror finish.


REGRINDING CAMSAND LIFTERS

I do not recommend using reground cams.

I do not recommend using reground lifters.


VALVE LASH

Mechanical Camshafts Hydraulic Camshafts Clearance


CHAPTER 10 u The Valve Train u Classroom Manual u Page 243 u Lab Manual u Page 245...

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