Thermostat Housing In S Ta Lla Tio - GMC 1989 Light Duty Truck Repair Manual

6A4-30 4.8 LITER L6
Figure 60—Adjusting the Valves
CHECKING VALVE TIMING
Tool Required:
J-8520 Dial Indicator Adaptor
When it becomes necessary to make a check of valve
tim ing, the procedure following may be used:
1. Loosen the nut at the #1 intake valve rocker arm,
swing the rocker arm away from the pushrod, then
remove the pushrod.
2. Install a dial indicator, along with J-8520 (figure 61).
Turn the crankshaft until the #2 exhaust valve opens
and the tim ing mark on the vibration damper is
aligned with the " 0 " mark on the timing marker.
3. P o sitio n th e d ia l in d ic a to r to m ea sure lifte r
m ovem ent and set indicator at zero. Turn the
crankshaft 360 degrees and read the indicator. On
co rre c tly tim e eng in es the in d ica to r w ill read
0.012-0.020-inch.
4. If the reading is not as shown, reset the indicator at
zero and turn the crankshaft 360 degrees, then read
th e in d ic a to r a ga in . If rea din g is now w ith in
specifications, the engine is timed properly.
Figure 6 1 — M easuring C am shaft Lobe Lift
5. The following chart shows indicator readings with
gears properly indexed for 4.8L engines and the
indicator readings resulting from improperly indexed
gears.
Engine
Camshaft Part Number
Valve Lift
Dial
Indicator
Readings
ROCKER ARM COVER AND
B-07858
INSTALLATION
|-»*-| Install or C onnect (Figures 4 and 5)
1. Gasket (8).
2. Rocker arm cover (7).
3. Bolts (3), clips (2) and reinforcements (4).
• Bolts (3) to 4.3 N-m (38 in. lbs.).
4. Gaskets (114).
5. Pushrod covers (179).
6. Bolts (178).
Q
• Bolts (178) to 9.0 N-m (80 in. lbs.).
WATER PUMP INSTALLATION
-►+ Install or C onnect (Figure 5)
1. Gasket (169).
2. Water pump (171).
3. Bolts (170).
THERMOSTAT HOUSING
-►+ Install or C onnect (Figure 4)
1. Gasket (49).
2. Thermostat housing (50).
3. Bolts (51).
&
B-03714
• Bolts (51) to 38 N-m (28 ft. lbs.).
4. Hose (47).
Gears Properly Indexed
One Tooth Advanced
One Tooth Retarded
PUSHROD COVER
INSTALLATION
Tighten
Tighten
Bolts (170) to 20 N-m (15 ft. lbs.).
INSTALLATION
Tighten
4.8L
3848000
0.405"
0.016" ± 0.004"
0.0379"
0.0068"