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Cylinder Heads and Valves

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Cylinder Heads and Valves Cylinder Heads Purpose Construction Cast Iron Cast Aluminum Overhead valve heads incorporate: Valves _at_ related components Coolant passages ... – PowerPoint PPT presentation

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Title: Cylinder Heads and Valves


1
Cylinder Heads and Valves
2
Cylinder Heads
  • Purpose
  • 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
Camshaft Follower
5
Camshaft Follower
6
Cylinder Heads
  • Modern designs incorporate
  • Squish area the un-concaved area in the
    combustion chamber designed to promote
    turbulence.
  • Quench area an area in the combustion chamber
    designed to cool the air/fuel mixture.

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8
Quench Area
9
Hemispherical Cylinder Heads
  • Hemi a Chrysler term for a symmetrical cylinder
    design.
  • Typically valves would be positioned directly
    opposite in the head with a sparkplug positioned
    between them.
  • Modern designs my incorporate two sparkplugs.
  • NOT exclusive to Chrysler!

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12
Hemi Head
13
Cylinder Heads
  • Surface-tovolume ratio the surface of the
    combustion chamber divided by the volume. Often
    near a 7.51 ratio.
  • If the surface area is too great fuel will
    condense on the surface area and not ignite.

14
Cylinder Heads
  • Valve shrouding placing the valves close to the
    walls of the combustion chamber to promote
    turbulence.
  • This area also has a tendency to reduce flow at
    high RPM.

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16
Cylinder Heads
  • Cross flow head design the practice of placing
    the intake port and the exhaust port on opposite
    sides of the cylinder head.

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18
Multiple Valves
  • Traditionally, combustion chambers would have one
    exhaust valve and one intake valve.

19
Multiple Valves
  • Three valve heads will have two intake and one
    exhaust valves.
  • Allows for a greater air/fuel charge
  • Lighter valves higher RPM
  • Greater turbulence generated

20
Multiple Valves
  • Four valves per cylinder two exhaust and two
    intake valves.
  • Pentroof design each pair of valves are inline
  • Hemispherical design each valve is on its own
    axis.
  • Allows for center placement of the sparkplug.

21
Pentroof Design
22
Hemispherical Design
23
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

24
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.

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26
Blown Head Gasket
27
Cylinder Head Removal
  • All aluminum cylinder heads should be removed
    with a reverse torque procedure.

28
Cylinder Head Resurfacing
  • Heads should be checked in five places for
    warpage, distortion, bends or twists.
  • Check manufacturers specifications, maximum
    tolerances usually around .004.

29
Checking for cylinder Warpage
30
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

31
Valve Guides
  • Steel insert on aluminum heads

32
Valve Guides Bore
33
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.

34
Valve Guide Wear
  • Guides often wear bell-mouthed due to rocker
    movement

35
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

36
Valve Stem To Guide Clearance Dial Indicator
Method
  • The valve is lifted off its seat to its maximum
    lift, locked into place and then checked with a
    dial indicator.
  • This method does not give the clearance directly
    and must be compared to specs.
  • The valve is lifted off its seat to its maximum
    lift, locked into place and then checked with a
    dial indicator.
  • This method does not give the clearance directly
    and must be compared to specs.

37
Valve Stem Wear
  • Measured with a micrometer at three separate
    locations.

38
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

39
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

40
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

41
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.

42
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

43
Valve Seat Service
44
Intake Exhaust Valves
  • Automotive valves are of a poppet valve design.

45
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

46
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

47
Sodium Filled Valve
48
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)

49
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

50
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 (355- 357)
  • Burnt
  • Cracked
  • Stressed
  • Necked

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54
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
  • Valve closed

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56
Valve Spring Tester
57
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.

58
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.

59
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

60
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
    (p.378)
  • Positive valve stem seals hold tightly onto the
    guide
  • O-rings controls oil between the spring and
    retainer

61
Valve Seals
62
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.

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