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)
Cylinder Heads
 Overhead
camshaft
heads will also
incorporate:
Camshaft(s)
Rocker
arms or
followers
Camshaft Follower
Camshaft Follower
Cylinder Heads
 Modern
designs
incorporate:
area – the unconcaved area in the
combustion chamber
designed to promote
turbulence.
 Quench area – an area in the
combustion chamber
designed to cool the air/fuel
mixture.
 Squish
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
shrouding –
placing the valves
close to the walls of the
combustion chamber to
promote turbulence.
 Valve
 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.
design – each pair of
valves are inline
 Hemispherical design – each
valve is on its own axis.
 Pentroof
 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 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.
Valve Guide Wear
 Guides
often wear “bellmouthed” due to rocker
movement
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.
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
Guide Inserts –
(integral) the old guide is
drilled oversized and
inserts are installed.
 Valve
 Pressed
fit
 May be steel or bronze
Valve & Seat Service
Intake & Exhaust Valves

Automotive
valves are
of a poppet
valve
design.
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
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 (tripleangle) 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.

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.
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
 Umbrella
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.
