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 dissi-
pation. Clean metal is a good heat conductor but
carbon insulates and retains heat. This increases
combustion chamber temperatures which causes
warping and burning.
+
Unburned carbon residue gums valve stems 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 areslightly 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
guidesfor wear as shown in Figure
2.
Use
a
hole gauge
to measure the valve guide. When clearance with stem
exceeds original clearance by that specified in
DIM-
ENSlONS
AND
CLEARANCES
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
Tappets are also replaceable from the valve chamber
after first removing the valve assemblies.
Valve Guide Remova1: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 driver.
4
tapered valve guides must face toward the valve head.
-1
Driving
out
old valve guides can cause
guide and tappet bore damage.
Do
not strike guide or tappet bores
wiih
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 coat the outer
edgeof each new guide with
oil.
Placeguide, notch-up,
in cylinder block and press in until guide stops or
protrudes
11
132
inch
(8.7
mm) from rocker box side of
block.
A
suggested method
of
installation is shown in
Figure
3.
ROD
5/16-18
HEX, NUT
(2
\
5/16
FLAT WASHER
(2
REQUIRED)
VT-1023
FIGURE
3.
VALVE GUIDE INSTALLATION
Valve Stem Seals:
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.
[BCAUTIONI
Removing a valve after installing valve
stem sealcan cause sealdamage.
Do
not allow valve stem groove to come in contact with
valve sfem seal after installation.
10-3
Redistribution or publication of this document,
by any means, is strictly prohibited.
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