Chevrolet 1977 light duty truck, Service Manual

Page: 462 / 861

2. Place ro u g h in g stone o r fo rm in g stone over pilot
and just clean up the valve seat. Use a stone cut to
specifications.
3. Remove ro ughing stone or fo rm in g stone from
pilot, place finishing stone, cut to specifications, over
pilot an d cut ju st e n o u g h m etal from the seat to provide
a smooth finish. R efer to specifications.
4. N a rro w down the valve seat to the specified
width.
N O T E : This operatio n is done by grin d in g the port
side with a 30 degree stone to lower seat and a 60
degree stone to raise seat.
5. Remove expanding pilot and clean cylinder
head carefully to remove all chips and grindings from
above operations.
6. M easure valve seat concentricity (fig. 6A-28).
VALVES
Valves th at are pitted can be refaced to the pro p er
angle, insuring correct relation between the head and
stem on a valve refacing m echanism . Valve stems which
show excessive wear, or valves
that are w arped
excessively should be replaced. W h e n a valve head which
is w arp ed excessively is refaced, a knife edge will be
g round on p a r t or all o f the valve head due to the
a m o u n t o f metal that must be removed to completely
reface. K nife edges lead to breakage, b u rn in g or p re ­
ignition due to heat localizing on this knife edge. If the
edge o f the valve h ead is less than 1 /3 2 " thick after
grinding, replace the valve.
Several different types o f eq u ip m en t are available
for refacing valves. The recom m endations o f the
m a n u fa c tu re r o f the eq u ip m e n t being used should be
carefully followed to attain p ro p e r results.
R e c o n d itio n in g
1. If necessary, dress the valve refacing m achine
Fig. 6A-28--M easuring Valve Seat C oncentricity
(Typical)
g rinding wheel to make sure it is smooth and true. Set
check at angle specified for valve. R efer to specifications.
2. C lam p the valve stem in the chuck o f the
machine.
3. Start the g rin d e r and move the valve head in
line with the grinder wheel.
4. T urn the feed screw until the valve head just
contacts wheel. Move valve back and forth across the
wheel and regulate the feed screw to provide light valve
contact.
5. Continue g rinding until the valve face is true
and smooth all a round the valve. If this makes the valve
head thin (1 /3 2 " min.) the valve must be replaced as the
valve will overheat and burn.
6. Remove valve from chuck and place stem in
" V " block. Feed valve squarely against g rin d in g wheel to
grind any pit from rocker arm end o f stem.
N O TE: Only the extreme end o f the valve stem is
hardened to resist wear. Do not grind end o f stem
excessively.
7. A fter cleaning valve face and cylinder h ead
valve seat o f g rinding particles, make pencil marks about
1 /4" ap art across the valve face, place the valve in
cylinder head and give the valve 1/2 turn in each
direction while exerting firm pressure on head o f valve.
8. Remove valve and check face carefully. If all
pencil marks have not been removed at the point o f
contact with the valve seat, it will be necessary to repeat
the refacing operating and again recheck for p roper
seating.
9. G r in d and check the rem ain in g valves in the
same m anner.
T O R S IO N A L D A M PER
R em o val
1. D ra in ra d iato r and remove as outlined in
Section 6B.
2. Remove fan belt an d (if so equipped) accessory
drive pulley and belt.
3. Install Tool J-23523 to d a m p e r and turn puller
screw to remove d a m p e r (fig. 6A-29). Remove tool.
In s ta lla tio n
1. Coat front cover oil seal contact area o f d a m p e r
with engine oil.
C A U T IO N :
It is necessary to use installer Tool
J -22197 to prevent the inertia weight section
fro m walking o ff the hub during installation o f
damper.
NOTE: The d a m p e r on the 292 L-6 should be
pulled on by using special tool J-23523 or
equivalent.
2. Attach d a m p e r installer Tool J-22197 to dam per.
Tighten fingers o f tool to prevent weight fro m moving
(fig. 6A-30).
3. Position d a m p e r on c ra n k sa h ft and drive into