Thermostat And Housing - GMC 1989 Light Duty Truck Repair Manual

Figure 39— Checking the Valve Seals
• Insert the valves into the proper ports.
3. Valve spring shims (if used).
4. Valve springs (20) with dampers (240).
5. Shields (18).
6. Rotators (17).
7. O-ring seals (16) and valve keys (15).
• C om press the valve spring, using J-8062
(figure 35). Compress the spring enough so
the lower valve stem groove can be clearly
seen.
• Push a new O-ring seal onto the valve stem.
The seal is to be installed on the stem's lower
groove. Make sure the seal is flat and not
twisted.
• Apply grease to the area of the upper valve
stem groove. Assemble the two valve keys,
using the grease to hold the keys in place.
Make sure the keys seat properly in the
groove.
• Release the compressor tool. Make sure the
valve keys stay in place.
• Repeat the preceding steps on the remaining
valves.
• Check each valve stem seal, using J-23738-A
(figure 39). Place the adapter cup over the
sh ie ld (18). O p e ra te th e va cuu m pum p.
Observe the vacuum pum p gage. No air
should be able to leak past the seal. If the
O-ring seal will not hold a vacuum, it may have
been damaged or improperly installed.
A
/
r i
A. G rin d o u t th is p o rtio n .
Figure 40—Scale for Checking Valve Spring
tp) M easure (Figures 34, 40, and 41)
• Valve spring installed height of each valve spring.
1. Use a narrow, thin scale. A cutaway scale (figure 40)
may be helpful.
2. Measure from the valve shim or spring seat to the
top of the shield (18) (figure 41).
3. If this measurement exceeds the figure given in
" Specifications," install valve spring seat shims of
s u ffic ie n t th ic k n e s s (betw een the s p rin g and
cylinder head) to give the desired measurement.
B-05247
NEVER shim the spring so as to give an installed
height under the specified figure.

THERMOSTAT AND HOUSING

The therm ostat is located in a housing bolted to the
front of the cylinder head (figure 4).
Thermostats consist of a restriction valve controlled by
a therm ostatic element. The restriction valve cracks or
just starts to open at a predetermined temperature and
continues to open as the engine coolant temperature
increases. To assure proper cooling and engine warm-up
it is important that the correct therm ostat be used. Refer
to the proper Truck Service M anual for the correct
therm ostat application.
4.8 LITER L6 6A4-21
a 3 4
Installed Height
i j i i
J
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B-05248