Warpage occurs chiefly in the upper stem due
to
its
exposure to intense heat. Out-of-round wear follows
when
the seat
is
pounded
by
a
valve
whose
head
is
not
in
line with the stem and guide. If
a
valve face is burned
or
warped,
or
if the stem is worn, install a new valve.
Too
much clearance in the intake guide admits air and
oil into the combustion chamber, upsetting carburetion,
increasing
oil
consumption, and making heavy
carbon
deposits. Carbon reduces heat dissipation. Clean metal
is a good heat conductor but carbon insulates and
retains heat. This increases combustion chamber temper-
atures which causes warping and burning.
1
*
Unburned carbon residue gums valvesterns and causes
them
to
stick in the guide. Deposits of hard carbon with
sharp points projecting become white hot and cause
pre-ignition and pinging.
Refinish valves that are slightly pitted or burned on an
accurate valve grinder.
If
valves are badly pitted
or
have
a thin margin when refacing, replace them.
VT-1020
FIGURE
2.
VALVE STEM AND VALVE GUIDE INSPECTION
Stems and Guides:
Always check valve stems and
guides for wear (Figure
2).
Use a hole gauge to measure
the valve guide. When clearance with stem exceeds that
specified in
DlMENSlONS AND CLEARANCH
replace
either valve or guide or both, as may be necessary.
Always regrind seat to make concentric with the newly
installed guide.
Worn valve stem guides can be replaced from inside the
valve chamber (a seal is provided behind the intake
valve guides only). The smaller diameter
of
the tapered
valve guides must face toward the valve head. Tappets
are also replaceable from the valve chamber after first
removing the valve assemblies.
b
Valve Guide Removal:
Before removing valve guides,
use an electric drill with a wire brush to remove carbon
and other foreign material from top surface of guides.
Failure to perform this operation may result in damage
to the guide bores. Drive the guides out with a hammer
and valve guide drive.
Y
-1
Driving out
old
valve guides can cause
guide and tappet bore damage.
Do
not strike
guide
or
tappet
bores
with
driver
during
removal.
Valve Guide Installation:
Run a small polishing rod
covered with crocus cloth through valve guide holes to
clean out carbon and other foreign materials. Place a
new gasket
on
the intake valve guide, and coatthe outer
edge of each new guide with
oil.
Place guide in cylinder
block and press in until guide protrudes
11/32
inch
(8.7
mm) from valve box side of block.
A
suggested
method
of
installation is shown in Figure
3.
(32
1-
ROD
'
NUT
5/16-18 HEX,
NUT
(2
\
5/16
FLAT
WASHER
(2
REQUIRED)
5/8"
(16
mm)
VT-1023
FIGURE
3.
VALVE
GUIDE INSTALLATION
Valve Stem Seals (intake only):
Do
not reuse valve stem
seals. Each time the valves are removed
from
cylinder
block, a new seal must be used when valve is reinstalled.
(QCAUTIONI
Removing a valve aflerinsta//ing valve
stem sealcan cause sealdamage.
Do
not allow valve stem groove to come in contact with
valve stem seal after installation.
10-3
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