GMC 1990 Light Truck Repair Manual page 369

Figure 30—Cleaning the Combustion Chambers
(Typical)
• Move the stem of the valve from side to side
using light pressure to obtain a clearance
reading. If clearance exceeds specifications, it
will be necessary to ream valve guide bores
for oversize valves as outlined later in this
manual.
— Valve spring tension. Use J 8056 or equivalent
(figure 33).
• 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 34). Replace the spring if
the length is not as specified.
Figure 31—Cleaning the Valve Guides (Typical)
GENERAL ENGINE MECHANICAL 6A-17
Figure 32—Measuring Stem to Bore Clearance
VALVE GRINDING
Valves that are pitted must be refaced to the proper
angle. Valve stems which show excessive wear, or valves
that are warped excessively must be replaced. When a
valve head which is warped excessively is refaced, a knife
edge will be ground on part or all of the valve head due to
the amount of metal that must be removed to completely
Figure 33—Measuring Valve Spring Tension
(Typical)
REPAIR