GMC T Series 1994 Repair Manual page 312

Figure 20— Cleaning the Valve Guides (Typical)
^ j| Measure (Figures 21, 22, and 23)
Tools Required:
J 8001 Dial Indicator (or equivalent)
J 9666 Valve Spring Tester
Valve stem to guide bore clearance.
— Excessive valve stem to guide bore clearance
will cause excessive oil consumption and may
cause valve breakage. Insufficient clearance will
result in noisy and sticky functioning of the
valve and disturb the engine's smoothness.
A. Clamp a dial indicator (J 8001 or equivalent) on
one side of the cylinder head rocker arm cover
gasket rail (figure 21).
Figure 21— Measuring Stem to Bore Clearance
(Typical)
B. Locate the indicator so movement of the valve
stem from side to side (crosswise to the head)
will cause a direct movement of the indicator
stem. The indicator stem must contact the side
of the valve stem just above the valve guide
bore.
C. Drop the valve head about 1.6 mm (1/16 inch)
off the valve seat.
D. Move the stem of the valve from side to side
using light pressure to obtain a clearance read­
ing. If clearance exceeds specifications, it will
be necessary to ream the valve guide bores for
oversize valves as outlined later.
• Valve spring tension, using J 9666 or equivalent
(figure 22).
— Compress the springs, with dampers removed,
to the specified height and check against the
specifications chart. Springs should be replaced
if not within 44 N (10 lbs.) of the specified load.
• Valve spring length (figure 23). Replace the spring
if the length is not as specified.