GMC 4000 Series Service Manual page 287

Sec. 6A
Page 276
GASOLINE ENGINES
Figure 3 2 — Use of Special Equipment for
Replacing Valve Spring (V6 Engine)
BOTTOM of stroke. Attach compressed air supply
line to adapter and turn on air supply. Air p res­
sure in cylinder will hold valves against seats
while spring and retaining parts are removed.
5. Assem ble valve spring com pressor (J-
21544) and nut on stud as shown in figure 32, then
with wrench, turn nut to force compressor down
100
. "
1 Exhaust Valve Seat
Ring
2 Exhaust Valve
3 Valve Rotator
4 Valve Spring
5 Valve Spring Cap
Figure 33— Sectional View of V6 Engine Cylinder
Head (Rotators Optional on 305E Engine)
G M C S E R V I C E M A N U A L
against valve spring cap meanwhile striking spring
cap lightly with hammer to unseat the valve locking
keys. Continue to turn the stud nut until spring is
compressed sufficiently to permit removal of the
two valve keys. Remove keys, then turn stud nut
counterclockwise to release the valve spring. Swing
the compressor away from valve, and remove the
spring and seat. Remove oil seal whenever spring
is removed from intake valve. Refer to figure 33
for valve spring and retaining parts installation.
position rotator on cylinder head with spring pilot
on top. Set valve spring on rotator with close-
wound coils toward cylinder head. Place spring
cap on spring and use compressor in same manner
as shown in figure 32 to compress valve spring.
On intake valves, install new oil seal in lower
groove in valve stem. Insert two keys in valve
stem grooves, then back off stud nut to release
pressure on valve spring. Be sure keys engage
groove in valve stem . Remove com pressor, stud
and nut from cylinder head.
from adapter. Remove adapter and install spark
plug and gasket. Tighten spark plug to 32 foot­
pounds torque.
sembly and tighten bracket bolts evenly to 20 to
25 foot-pounds torque.
Replacement" for additional information regarding
rocker arm shaft and bracket installation.
temperature is reached, check valve lash. Clear­
ance should be 0.012 inch at intake valves and
0.018 inch at exhaust valves.
models with V6 gasoline engines by following the
x 3 0
instructions outlined in following paragraphs. Be
.0 6 5 '
sure to install new head gasket and manifold gas­
Valve Key
kets when replacing cylinder heads. It will facil­
Oil Seal
itate the procedure on Tilt-Cab Models if the en­
Intake Valve
gine shield on cab rear support is removed.
Cylinder Head
CYLINDER HEAD REMOVAL
from tilt cab model, the transmission control rods
must first be removed.
CAUTION: DO NOT turn off the air
supply while spring and retaining parts
are removed from valve, as the valve may
fall out of guide and drop into cylinder.
6. If valve rotator is replaced, be sure to
7. Turn off air supply, and disconnect air line
8. Install rocker arm shaft and bracket a s­
NOTE: Refer to "Valve Operating Mechanism
9. Start engine and when normal operating
10. Install valve rocker arm cover and gasket.
CYLINDER HEAD REPLACEMENT
Cylinder head can be replaced on most truck
NOTE: When left-hand head is to be removed