6Cylinder 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.
9Hemispherical 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!
13Cylinder HeadsSurface-to–volume ratio – the surface of the combustion chamber divided by the volume. Often near a 7.5:1 ratio.If the surface area is too great fuel will condense on the surface area and not ignite.
14Cylinder HeadsValve 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.
18Multiple ValvesTraditionally, combustion chambers would have one exhaust valve and one intake valve.
19Multiple ValvesThree valve heads will have two intake and one exhaust valves.Allows for a greater air/fuel chargeLighter valves = higher RPMGreater turbulence generated
20Multiple ValvesFour valves per cylinder – two exhaust and two intake valves.Pentroof design – each pair of valves are inlineHemispherical design – each valve is on its own axis.Allows for center placement of the sparkplug.
23Intake - Exhaust PortsThe passageways in the cylinder head that lead to/from the combustion area.Intake:Larger ports = more airflowSmaller ports = better velocity for low RPM operationLonger ports = better atomization on carb and TBIShorter ports = denser A/F charge
24Coolant travels through the cylinder head from the engine block. Coolant PassagesCoolant 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.
33Valve Stem To Guide Clearance Always check manufacturers specsIntake 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.
34Guides often wear “bell-mouthed” due to rocker movement Valve Guide WearGuides often wear “bell-mouthed” due to rocker movement
35Guides are checked in 3 locations Valve Guide WearGuides are checked in 3 locationsWith a small-hole gauge then measured with a micrometerOr checked with a small bore gauge
36Valve Stem To Guide Clearance – Dial Indicator Method The valve is lifted off it’s seat to it’s 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.
37Valve Stem WearMeasured with a micrometer at three separate locations.
38Valve 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
39Valve 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 )The guide is then reamed to attain proper clearanceNot recommended for clearances +.006
40Valve 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 )The guide is then reamed to attain proper clearanceNot recommended for clearances +.006
41Valve 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.
42Valve Stem To Guide Clearance Correction Valve Guide Inserts – (integral) the old guide is drilled oversized and inserts are installed.Pressed fitMay be steel or bronze
44Intake & Exhaust Valves Automotive valves are of a poppet valve design.
45Stainless steel Aluminum Valve Materials May be aluminized to prevent corrosionAluminumHardened valve tips and facesStellite (nickle, chromium and tungsten) valve tips and facesStellite is non-magnetic
46Valve MaterialsSodium-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-treatedMay be of a two-piece design
54Valve SpringsA 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 openValve closed
57Valve ReconditioningThe 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.
58Valve 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.
59All compound must be removed prior to service Valve LappingThe use of valve compound and a suction cup stick to establish a patternMay be done to “freshen” the seat and face areasAlso used to check the contact pattern while cutting valve seatsAll compound must be removed prior to service
60Valve SealsValve 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 guideO-rings – controls oil between the spring and retainer
62Checking 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.