GMC T Series 1994 Repair Manual page 541

Valve Guides and Valve Seats
N O T IC E : V a lv e s e a t s
i n d u c t i o n - h a r d e n e d . E x c e s s i v e r e m o v a l o f
s t o c k m a y r e s u l t in
s e a ts .
Assemble (Figures 52, 53, and 54)
*
Tool Required:
J 8062 Valve Spring Compressor
1. Prechambers (272) (if removed) (figure 54).
A. Align the locating notches. The prechamber will
fit correctly in only one position.
B. Tap into place. Use a 32-mm (1 1/4-inch) sock­
et.
m
Measure
• Prechamber installed depth. The prechamber
should be flush to a maximum of 0.05 mm
(0.002 inch) protrusion.
• Make the measurement at two or more
p o in ts on th e p re c h a m b e r w h e re the
prechamber seats on the head gasket shield
and sealing ring.
• Measure the difference between the flat of
the prechamber and the flat surface of the
cylinder head.
• The prechamber must not protrude out of
the cylinder head more than 0.05 mm (0.002
inch).
• The prechamber must not be recessed into
the cylinder head.
2. Valves (207 and 208).
A. Lubricate the valve stems with engine oil.
B. Insert the valves into the proper ports.
3. Shims.
4. Valve seals (409) (exhaust valves only). Install the
valve seals over the valve stems and seat them
against the heads.
5. New valve springs with dampers (410).
6. Shields (408).
7. Caps (407) (intake valves only).
8. Rotators (411) (exhaust valves only).
9. O-ring seals (409) and valve keepers (406).
A. Compress the valve spring, using J 8062 (figure
53). Compress the spring enough so the lower
valve stem groove can be clearly seen.
B. Push a new 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.
C. Apply a small amount of grease to the area of
the upper valve stem groove. Assemble the two
valve keepers using the grease to hold the
keepers in place. Make sure the keepers seat
properly in the groove.
D. Release the compressor tool. Make sure the
valve keepers stay in place.
E. Repeat the preceding steps on the remaining
valves.
o n 6 .5 L e n g in e s a r e
d a m a g e to t h e v a lv e
| j | Measure (Figures 57 and 58)
Valve spring installed height of each valve spring,
as follows:
1. Use a narrow, thin scale. A cutaway scale may
be helpful (figure 57).
2. Measure from the valve shim or spring seat to
the top of the shield (figure 58).
3. If this measurement exceeds the figure given in
" Specifications," install valve spring seat shims
of sufficient thickness (between the spring and
cylinder head) to give the desired measure­
ment. Never shim the spring so as to give an
installed height under the specified figure.
GLOW PLUGS
Inspect
• Glow plugs for stripped threads and damage.
Replace the glow plugs if the tips are cracked,
bulged, or broken.
A
TT r j iTT T . | H | | | P p , , | | ,r T
1 _______ 1_______ 3
A. Grind out this portion.
Figure 57— Cutaway Scale
| . j | | ' i | | | j | , V | | | . | T | r | „ | [ J p T p p T ' l ' r r
4_______ ____ _
B5248