6-52
1968
PONTIAC
SERVICE
MANUAL
will
permit oil to be pulled
Into
the combustion
chamber, causing
fouled
spark plugs and clogged
piston
rings. Oil deposited on valve
heads
will
carbonize and burn, causing valves
•
to leak
with
resultant loss of engine power. Therefore, valves
must
operate
properly and If Inspection discloses
any malfunction of valves, the trouble must be cor-
rected to avoid future
damage
to valves or related
engine parts.
1.
Inspect valves and
seats
to determine condition
before cleaning.
Also
water
passage
plugs for
evi-
dence
of leakage.
2.
Clean valves thoroughly to remove deposits
from
head and stem.
3. Clean and Inspect cylinder head as
follows:
a. Clean carbon deposits
from
combustion
chambers and all sludge or
foreign
matter
from
other'
areas
of cylinder head. If a
scraper
or
wire
brush is used for cleaning, use
care
to prevent
damage
to valve
seats.
CAUTION;
To
prevent
damage to
valve
seat
it is
good
practice
to
keep
wire
brush
well
away
from
seat.
b.
-
Clean cylinder head thoroughly, using suit-
able cleaning equipment.
4.
Clean valve guides thoroughly, using valve guide
cleaner J 8101 (Fig. 6-89).
5.
Visually
inspect valve guides for evidence of
wear, especially the end toward the spring
seat.
If
a guide is scored or galled,
Install
valve
with
proper oversize stem according to procedure.
6. Clean valve springs and inspect to see that
they meet specifications.
J-8101
/
7. Clean push rods and thoroughly clean out oil
passage
through center of rod. Inspect to see that
the rod is straight.
8. Clean rocker arms and rocker arm balls, and
visually
inspect for evidence of wear.
9. Clean spark plugs as outlined in
ELECTRICAL
SECTION.
10.
Clean and inspect valve
lifters.
VALVES
AND
SEATS-RECONDITION
1. Reface valves and
seats
as
follows:
Valves
should be ground on a special bench grinder
designed specifically for this purpose and
built
by a
reputable manufacturer. Valve
seats
should be
ground
with
reputable power
grinding
equipment
having
stones
of the correct
seat
angle and a suitable
pilot
which
pilots in the valve stem guide. To
ensure
positive
sealing of the valve face to its
seat,
the
grinding
stones
should be carefully refaced before
any
grinding
is done. Intake valve
seat
angle is 30°,
exhaust valve
seat
angle is 45°. Intake valve face
angle is 29° and exhaust valve face angle is 44°.
This
will
provide hairline contact between valve and
seat
to provide positive sealing and reduce build-up
of
deposits on seating
surfaces
(Fig. 6-90).
DO
NOT USE
RE
FACING
EQUIPMENT
EXCES-
SIVELY;
only
enough material should be removed
to
true up
surfaces
and remove pits. The valve head
will
run hotter as its thickness is diminished; there-
fore,
if valve face cannot be cleaned up
without
grinding
to point where outside diameter of valve
has a
sharp
edge,
the valve should be replaced.
Whenever it is
necessary
to replace a valve, the
new valve should be of the
same
stem diameter as
the valve removed (unless the valve guide is reamed
to
provide proper
fit).
Width
of exhaust valve
seats
should be 1/16"
(.048"-.070
TT
). Intake valve
seat
should be between
3/64" and 1/16" (.045"-.071"). If
seat
width
is
excessive it should be narrowed by
grinding
with
a
A—SEAT
WIDTH
Fig.
6-89
Cleaning
Valve
Guide
Fig.
6-90
Valve
Sear
and
Face
Angles
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