Service Manual

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.
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 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 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 tapered
valve guides must face toward the valve head. Tappets
are also replaceable from the valve chamber after first
removing the valve assemblies.
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.
guide and tappet bore damage. Do
Driving out old valve guides can cause
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 coat the 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.
ROD
VALVE GUIDE
5/16-18 HEX NUT
(2 REQUIRED)
NUT
5/16-18 THREADED ROD
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.
Removing a valve after installing valve
stem seal can cause seal damage.
Do
not allow valve stem groove to come in contact with
valve stem seal after installation.
10-3