Cylinder Heads and Valves

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Cylinder Heads and Valves
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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)

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Cylinder Heads

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

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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 (ideally) a spark-plug
  positioned between them.
• Modern designs my incorporate two spark-plugs.
• NOT exclusive to Chrysler!

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Hemi Head
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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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Traditional Arrangement

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

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Multiple Valves

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

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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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Gasket Matching

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

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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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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 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 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 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 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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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 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 height
• Valve closed height

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Valve Spring Tester
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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 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 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

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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
  
• Positive valve stem seals hold tightly onto the
  guide
• O-rings controls oil between the spring and
  retainer

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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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Camshafts
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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

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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).

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When installing externally oiled cam bearings it
is essential that the holes in the bearings
lineup with the oil passages in the block
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Camshaft

• Pushrod engines have the cam located in the
  block.

• Cam is supported by the block and the cam
  bearings.

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Camshaft

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

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Overhead Camshafts

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

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Overhead Camshafts

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

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Camshaft Operation
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Bucket Design
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Camshaft Followers
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Rocker Arms
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Design

• A cam casting will include
• Lobes
• Bearing journals
• Drive flange (gear)

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Design

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

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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.

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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

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Flat tappet Lifters
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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.

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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.

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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.

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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!

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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.

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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.

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Hydraulic Lifters (tappets)

• Hollow cylinders fitted with a plunger, check
  valve, spring and push-rod seat.

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Hydraulic Lifters (tappets)
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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.

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• 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.

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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.

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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

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Hydraulic Lifter Preload

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

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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.

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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.

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Solid Flat-tappet and Roller

• Oil is diverted through the pushrods via a
  pushrod seat.

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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.

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Cam Specifications

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

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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.

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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.

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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.

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Duration

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

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Duration

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

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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

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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.

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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

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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

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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

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Camshaft (Valve) Timing

• Some designs do not provide alignment marks and
  require special tools for proper timing

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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

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Adjustable Camshaft Gear
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