Cylinder Heads and Valves

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Cylinder Heads and Valves
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Cylinder Heads

• Purpose
• Construction
• Cast Iron
• Cast Aluminum
• Overhead valve heads incorporate
• Valves _at_ related components
• Coolant passages
• Valve operation mechanism(s)

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Cylinder Heads

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

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Camshaft Follower
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Camshaft Follower
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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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Quench Area
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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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Hemi Head
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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.

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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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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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Multiple Valves

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

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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

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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.

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Pentroof Design
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Hemispherical Design
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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

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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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Blown Head Gasket
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Cylinder Head Removal

• All aluminum cylinder heads should be removed
  with a reverse torque procedure.

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Cylinder Head Resurfacing

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

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Checking for cylinder Warpage
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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

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Valve Guides

• Steel insert on aluminum heads

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Valve Guides Bore
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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.

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Valve Guide Wear

• Guides often wear bell-mouthed due to rocker
  movement

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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

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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.

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Valve Stem Wear

• Measured with a micrometer at three separate
  locations.

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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

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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

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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

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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.

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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

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Valve Seat Service
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Intake Exhaust Valves

• Automotive valves are of a poppet valve design.

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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

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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

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Sodium Filled Valve
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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)

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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

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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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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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Valve Spring Tester
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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.

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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.

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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

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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

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Valve Seals
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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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