Cylinder Heads and Valves - PowerPoint PPT Presentation

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Cylinder Heads and Valves

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Title: PowerPoint Presentation Author: Robert Ward Last modified by: rward Created Date: 11/29/2006 8:19:53 PM Document presentation format: On-screen Show (4:3) – PowerPoint PPT presentation

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Title: Cylinder Heads and Valves


1
Cylinder Heads and Valves
2
Cylinder Heads
  • Purpose regulates the air/fuel in/out of the
    engine
  • Construction
  • Cast Iron
  • Cast Aluminum
  • Overhead valve heads incorporate
  • Valves _at_ related components
  • Coolant passages
  • Valve operation mechanism(s)

3
Cylinder Heads
  • Overhead camshaft heads will also incorporate
  • Camshaft(s)
  • Rocker arms or followers

4
Hemispherical Cylinder Heads
  • Hemi a Chrysler term for a symmetrical cylinder
    design.
  • Typically valves would be positioned directly
    opposite in the head with (ideally) a spark-plug
    positioned between them.
  • Modern designs my incorporate two spark-plugs.
  • NOT exclusive to Chrysler!

5
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6
Hemi Head
7
Cylinder Heads
  • Cross flow head design the practice of placing
    the intake port and the exhaust port on opposite
    sides of the cylinder head.

8
Traditional Arrangement
  • Traditionally, combustion chambers would have one
    exhaust valve and one intake valve.

9
Multiple Valves
  • Four valves per cylinder two exhaust and two
    intake valves.
  • Pentroof design each pair of valves are inline

10
Intake - Exhaust Ports
  • The passageways in the cylinder head that lead
    to/from the combustion area.
  • Intake
  • Larger ports more airflow
  • Smaller ports better velocity for low RPM
    operation
  • Longer ports better atomization on carb and TBI
  • Shorter ports denser A/F charge

11
Gasket Matching
  • Using an intake gasket as a template to port
    the heads

12
Coolant Passages
  • Coolant travels through the cylinder head from
    the engine block.
  • Cylinder head gaskets may be designed to restrict
    coolant flow rate.
  • Often a source for corrosion and leakage.

13
Blown Head Gasket

14
Cylinder Head Removal
  • All aluminum cylinder heads should be removed
    with a reverse torque procedure.

15
Cylinder Head Resurfacing
  • Heads should be checked in five places for
    warpage, distortion, bends or twists.
  • Check manufacturers specifications, maximum
    tolerances usually around .004.

16
Valve Guides
  • The bore in the cylinder head that supports and
    controls lateral valve movement.
  • Often integral on cast iron heads
  • Always an insert on aluminum heads

17
Valve Guides
  • Steel insert on aluminum heads

18
Valve Stem To Guide Clearance
  • Always check manufacturers specs
  • Intake valve will typically be .001 to .003
  • Exhaust valve will typically be .002 to .004
  • The exhaust valve stem clearance will generally
    be greater due to the higher operating
    temperatures.

19
Valve Guide Wear
  • Guides are checked in 3 locations
  • With a small-hole gauge then measured with a
    micrometer
  • Or checked with a small bore gauge

20
Valve Stem Wear
  • Measured with a micrometer at three separate
    locations.

21
Valve Stem To Guide Clearance Correction
  • Oversized Valve Stems the guide is reamed to
    accept a larger stem.
  • Must use a valve with an oversized stem.
  • Reduced flow rate

22
Valve Stem To Guide Clearance Correction
  • Valve guide Knurling a tool is driven into the
    guide that displaces metal thus reducing the
    inside diameter of the guide. (p. 340-341)
  • The guide is then reamed to attain proper
    clearance
  • Not recommended for clearances .006

23
Valve Stem To Guide Clearance Correction
  • Valve guide replacement (insert) the old guide
    is driven out and a replacement guide is driven
    in.
  • The guide may require reaming to achieve proper
    stem to guide clearance.

24
Valve Stem To Guide Clearance Correction
  • Valve Guide Inserts (integral) the old guide is
    drilled oversized and inserts are installed.
  • Pressed fit
  • May be steel or bronze

25
Valve Seat Service
26
Intake Exhaust Valves
  • Automotive valves are of a poppet valve design.

27
Valve Materials
  • Stainless steel
  • May be aluminized to prevent corrosion
  • Aluminum
  • Hardened valve tips and faces
  • Stellite (nickle, chromium and tungsten) valve
    tips and faces
  • Stellite is non-magnetic

28
Valve Materials
  • Sodium-filled a hollow stem filled with a
    metallic sodium that turns to liquid when hot
    (heat dissipation).
  • Exhaust valves are largely comprised of a
    chromium material (anti-oxidant) with nickel,
    manganese and nitrogen added.
  • May be heat-treated
  • May be of a two-piece design

29
Intake Exhaust Valves
  • Valves are held into place by a retainer and
    keeper.
  • Aluminum heads will have a separate spring seat
    (iron heads will have integral seats)

30
Valve Seats
  • Integral seats cast iron heads
    induction-hardened to prevent wear
  • Valve seat inserts typically aluminum heads
    hardened seats are pressed into the heads

31
Valve Inspection
  • Valve tips should not be mushroomed
  • Most valve damage is due to excessive heat or is
    debris forged.
  • Replace any valve that appears Burnt
  • Cracked
  • Stressed
  • Necked

32
Valve Springs
  • A spring winds-up as it is compressed this
    causes the valve to rotate.
  • May have inside dampers to control vibration.
  • Springs are camshaft specific.
  • Squareness ( (-) .060)
  • Spring free height ( (-) .060)
  • Compressed force ( (-) 10)
  • Valve open height
  • Valve closed height

33
Valve Spring Tester
34
Valve Seat Reconditioning
  • The angle of the valve seat is reconditioned.
  • Often 3 stage (triple-angle) to promote flow and
    overhang.
  • May be done with seat stones
  • May also be done with a SERDI type set-up where
    the 3 angles are cut with one cutting tip.

35
Valve Reconditioning
  • The stem is lightly chamfered to insure proper
    fit in the valve grinder.
  • The face of the valve is reground using a valve
    grinder. (45 or 30 degrees typical).
  • Interference angle the practice of grinding the
    face 1degree less than the seat angle.
  • The valve must retain its margin area.
  • the stem should be ground ½ the value that the
    face was ground with nonadjustable rockers.

36
Valve Lapping
  • The use of valve compound and a suction cup stick
    to establish a pattern
  • May be done to freshen the seat and face areas

37
Valve Lapping
  • The use of valve compound and a suction cup stick
    to establish a pattern
  • May be done to freshen the seat and face areas
  • Also used to check the contact pattern while
    cutting valve seats
  • All compound must be removed prior to service

38
Valve Seals
  • Valve Seals are designed to allow sufficient
    lubrication of the valve stem/guide and also
    control oil consumption.
  • Umbrella seals hold tightly onto the valve stem
  • Positive valve stem seals hold tightly onto the
    guide
  • O-rings controls oil between the spring and
    retainer

39
Checking Installed Height
  • If a valve seat and face are cut the valve will
    sit lower in the head.
  • The result is that the stem will sit higher on
    the top of the head.
  • This will cause the springs to have improper
    tension.
  • Installed height is measured and shims are added
    under the spring to compensate.

40
Camshafts
41
Camshaft
  • The camshaft rotates ½ times the crankshaft or
  • once per four-cycle stroke.
  • The camshaft may operate the
  • Valve train
  • Mechanical fuel pump
  • Oil pump
  • Distributor

42
Camshaft
  • Major function - operate the valve train.
  • The lobes on the cam open the valves against the
    pressure of the valve springs.
  • Bearing journal can be internally or externally
    lubricated (oiled).

43
When installing externally oiled cam bearings it
is essential that the holes in the bearings
lineup with the oil passages in the block
44
Camshaft
  • Pushrod engines have the cam located in the
    block.
  • Cam is supported by the block and the cam
    bearings.

45
Camshaft
  • Cam may or may not be held in place by a thrust
    plate.
  • Most roller camshafts are held in by a thrust
    plate.

46
Overhead Camshafts
  • Overhead camshafts are either belt or chain
    driven and are located in the cylinder heads.

47
Overhead Camshafts
  • Will use one of the following
  • Cam followers
  • Rocker arms
  • May have a one piece lifter rocker design
  • A bucket design

48
Camshaft Operation
49
Bucket Design
50
Camshaft Followers
51
Rocker Arms
52
Design
  • A cam casting will include
  • Lobes
  • Bearing journals
  • Drive flange (gear)

53
Design
  • A cam casting may include
  • Oil pump drive gear(s)
  • Fuel pump eccentric (mechanical fuel pump)

54
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55
Classification
  • Camshafts are of one of four types
  • Hydraulic flat-tappet
  • Hydraulic roller
  • Solid flat-tappet
  • Solid roller
  • This designation is actually determined by the
    lifter design.

56
Hydraulic flat-tappet
  • The lifter is spring and oil loaded to allow
    for compensation.
  • Traditional O.E. style (1950s mid 90s)
  • Used with flat or convex-faced lifters
  • Generally cast iron or hardened steel
  • Requires a break-in period to establish a wear
    pattern

57
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58
Flat tappet Lifters
59
Hydraulic flat-tappet
  • Most cams are coated at the factory with
    manganese phosphate . This gives the cam a dull
    black appearance. This coating is to absorb and
    hold oil during the break-in period.

60
Hydraulic flat-tappet
  • Most late model designs use a convex bottom
    (.002) to encourage lifter rotation.
  • This rotation helps reduce lifter and (or) bore
    wear.
  • The Cam lobe will also be slightly tapered
    (.0007 - .002).
  • This provides for a wider contact pattern.

61
Hydraulic flat-tappet
  • Camshaft break-in
  • The lobes of the cam and the bottom of the
    lifters must be coated with a molydisulfide
    lubricant often called cam lube.
  • This insures that the cam is properly lubricated
    during break-in.

62
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63
Hydraulic flat-tappet
  • Camshaft break-in
  • Typical procedure
  • Maintain 1,500 RPM for 10 - 20 minutes
  • Drain the engine oil a immediately afterwards
  • Check the recommended procedure and lube for your
    particular cam!

64
Hydraulic Roller
  • The lifter is spring and oil loaded to allow
    for compensation.
  • The contact between the cam and lifters are
    separated by a steel roller.
  • This roller reduces friction.
  • Lifters cannot be allowed to rotate within the
    lifter bore.

65
Hydraulic Roller
  • A roller camshaft is generally made of
    non-hardened steel.
  • The lobes must be finished by the manufacturer
    prior to assembly
  • there is no break-in period.

66
Hydraulic Lifters (tappets)
  • Hollow cylinders fitted with a plunger, check
    valve, spring and push-rod seat.

67
Hydraulic Lifters (tappets)
68
Hydraulic Lifters
  • The oil passed through the check valve exits
    through the hole in the push rod seat.
  • The oil then passes through the pushrod to
    lubricate the rocker arms.

69
  • Engine oil pressure forces oil into the lifter
    through the oil inlet holes.
  • A check valve and ball hold most of the oil
    inside the lifter hydro-locking the plunger
    inside the cylinder.

70
Hydraulic Lifter Preload
  • Also called valve lash.
  • The distance between the pushrod seat and
    snap-ring when the lifter is resting on its base
    circle.
  • Typical values range from .020 to .045.
  • Check manufacturers specifications.

71
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72
Hydraulic Lifter Preload
  • Adjusted by
  • Adjustable rocker arms
  • Often referenced by turns past zero lash
  • Non-adjustable rocker arms
  • Longer or shorter pushrods
  • Shim or grind rocker stands

73
Hydraulic Lifter Preload
  • Necessary if
  • Cylinder head has been decked
  • Cam has been changed
  • Altered head gaskets
  • Camshaft is worn
  • An engine rebuild

74
Hydraulic Lifter Valve-floatNOT GOOD
  • The lifter fills with oil faster than it can
    purge it. This raises the lift of the camshaft.
  • Usually caused by excessive RPM.
  • May damage valves, pushrods, pistons etc.

75
Solid Flat-tappet and Roller
  • No internal hydraulic absorption.
  • Allows for a more consistent valve lift,
    especially at high RPM.
  • Noisy when cold, more frequent and precise
    valve-lash adjustments required.

76
Solid Flat-tappet and Roller
  • Oil is diverted through the pushrods via a
    pushrod seat.

77
Solid Flat-tappet and Roller
  • No lifter preload valve lash only.
  • Lash values may be given hot or cold
  • Typical values range from .002 - .005.

78
Cam Specifications
  • Lift
  • Duration
  • Valve overlap
  • Lobe center (separation angle or lobe spread)

79
Lobe Lift
  • The amount the cam lobe lifts the lifter
  • Expressed in decimal inches
  • As lift increases the forces on the entire valve
    train also increase.

80
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81
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82
Lobe Lift
  • Asymmetrical design the amount of lift between
    the intake and exhaust lobes is different.
  • Symmetrical design - the amount of lift between
    the intake and exhaust lobes is the same.

83
Duration
  • The number of degrees of crankshaft rotation for
    which the valve is lifted off of the seat.
  • If the amount of degrees that the intake and
    exhaust valve are open differ it is of an
    asymmetrical design.

84
Duration
  • Usually expressed as one of two values
  • Duration (at zero lash)
  • Duration at .050 lift preferred method
  • Compensates for tappet styles and clearances

85
Duration
  • More duration rougher idle and better high RPM
    performance
  • Less duration smoother idle and better low RPM
    performance

86
Valve Overlap
  • The number of degrees of crankshaft rotation that
    both valves are off of their seat (between the
    exhaust and intake strokes).
  • Lower overlap a smoother idle and better low
    RPM operation
  • Higher overlap better high RPM operation

87
Valve Overlap
  • Having the exhaust valve still open when the
    intake starts to open uses the exhaust "pull" out
    the exhaust port to help start the intake charge
    entering the chamber -- before the piston has
    started down and has generated it's own vacuum.

88
Lobe Separation Angle
  • The difference, in degrees, between the center of
    the intake lobe and the center of the exhaust
    valve.
  • The smaller the angle the greater the valve
    overlap
  • The larger the angle the less the overlap
  • Link to LSA effects

89
Camshaft (Valve) Timing
Pushrod- Type Engine
  • It is crucial that the crankshaft, camshaft and
    balancing shaft (if equipped) are timed
    correctly.
  • This is often achieved by aligning timing marks
    on the gears

90
Camshaft (Valve) Timing
V-type DOHC Design
  • Modern DOHC motors may incorporate chains and
    belts on the same motor
  • Some of these designs are quite elaborate

91
Camshaft (Valve) Timing
  • Some designs do not provide alignment marks and
    require special tools for proper timing

92
Camshaft Degreeing
  • Advanced cam timing
  • The camshaft is slightly ahead of the crankshaft
  • More low speed torque
  • less high RPM power
  • Retarded timing
  • The camshaft is slightly behind the crankshaft
  • More high RPM power
  • Reduced low RPM torque

93
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94
Adjustable Camshaft Gear
95
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