Pontiac FIREBIRD 1972 Service Manual page 540

6-28 1972 PONTIAC SERVICE MANUAL
positive sealing of the valve face to its seat, the grind-
ing stones should be carefully refaced before any
grinding is done.
Intake and exhaust valve seat angle is 46", while both
valve face angles are 45". This will provide hairline
contact between valve and seat to provide positive
sealing and reduce build-up of deposis on seating
surfaces (Fig. 6-39).
CAUTION:
DO NOT USE REFACING
EQUIPMENT EXCESSIVEL only enough
matenal should be removed to true up surfaces
and remove pits. The valve head will run hotter
as it's thickness is diminishe4 therefore, if
valve face cannot be cleaned up without grind-
ing to a 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 pro vide proper fit).
2. Width of exhaust valve seats should be .0625" to
.0938". Intake valve seats should be .03 13" to .0625"
wide. If seat width is excessive, it should be narrowed
by grinding with a flat stone. This is the only method
that should be used to narrow the seat.
3. Check concentricity of valve seat and valve guide by
using a suitable dial indicator or prussian blue. When
using a dial indicator, total runout should not exceed
.002".
When prussian blue is used, a light coat should be
applied to the face of the valve only and the valve
rotated in its seat. If blue appears all the way around
A-SEAT WIDTH
0-FACE ANGLE
C-SEAT ANGLE
D-VALVE FACE
/ ,
GRIND WITH FLAT STONE
/
SEAT
WIDTH
I
Fig. 6 - 3 9 Valve Seat and Face Angles
the valve seat, the valve seat and the valve guide are
concentric with one another.
4. Check concentricity of valve stem and valve face.
After cleaning prussian blue from valve and seat
lightly coat valve seat with prussian blue again and
rotate valve in guide. If blue appears all the way
around the valve, the valve stem and face are concen-
tric with each other.
Both tests in steps 2 and 3 are necessary to ensure
proper valve seating.
If it is necessary to gnnd any pits from rocker arm
end of valve stem, feed end squarely against gnnding
wheel. Only the extreme end of the valve stem is
hardened to resist wear. Do not grind end exces-
sively.
ASSEMBLE
1. Starting with No. 1 cylinder, place the exhaust valve
in the port and place the valve spring and cap in
position. Place spring and rotator on exhaust valves.
Then using suitable spring compressor, compress the
spring and install the oil seal and valve locks. See that
the seal is flat and not twisted in the valve stem
groove and that the seat locks properly in the valve
stem groove (Fig. 6-35).
Place valve springs in position with the closed coil
end to ward the cylinder head.
2. Assemble the remaining valves, valve springs,
shields, spring caps, oil seals and valve locks in the
cylinder head. Check seals by placing a vacuum cup
over valve stem and cap, squeeze vacuum cup to
make sure no oil leaks past oil seal.
3. Install cylinder head as previously described.
VALVE SPRING INSTALLED HEIGHT
Check the installed height of the valve springs, using a
narrow, thin scale to measure from the top of the shim, or
spring seat, in the head to the top of the valve spring
shield. If this is found in excess of 1-23/32", install a valve
spring seat shim approximately 1/16" thick above the
spring seating surface in the head. At no time should the
spring be shimmed to give an installed height of less than
1-21/32" (Fig. 6-40).
HARMONIC BALANCER
REMOVE
1. Drain cooling system and disconnect radiator hoses
at radiator.