Cylinder Heads and Valves

Cylinder Heads Purpose Construction Cast Iron Cast Aluminum Overhead valve heads incorporate: Valves @ related components Coolant passages Valve operation mechanism(s)

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

Camshaft Follower

Camshaft Follower

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.

Quench Area

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!

Hemi Head

Cylinder Heads Surface-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.

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.

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

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

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

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.

Pentroof Design

Hemispherical Design

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

Coolant travels through the cylinder head from the engine block. 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.

Blown Head Gasket

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

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

Checking for cylinder Warpage

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

Valve Guides Steel insert on aluminum heads

Valve Guides Bore

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.

Guides often wear “bell-mouthed” due to rocker movement Valve Guide Wear Guides often wear “bell-mouthed” due to rocker movement

Guides are checked in 3 locations 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

Valve 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.

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

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

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

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

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.

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

Valve & Seat Service

Intake & Exhaust Valves Automotive valves are of a poppet valve design.

Stainless steel Aluminum Valve Materials 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

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

Sodium Filled Valve

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)

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

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

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

Valve Spring Tester

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.

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.

All compound must be removed prior to service 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

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

Valve Seals

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.