chevrolet truck Light Duty Truck 1994 Series, Repair Manual

Page: 313 / 919

REPAIR
VALVE GRINDING
Pitted valves must be refaced to the proper angle.
Valve stems that show excessive wear, or valves that
are warped excessively must be replaced. When an
excessively warped valve head 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 complete­
ly reface. Knife edges lead to breakage, burning, or
preignition due to heat localizing on this knife edge. If
the edge of the valve head is less than 0.80 mm (1/32
inch) after grinding, replace the valve (figure 24).
Several different types of equipment are available for
refacing valves. The recommendation of the manufac­
turer of the equipment being used should be carefully
followed to attain the proper results.
Refer to “ Specifications” in the proper section for
valve face angle specifications.
VALVE SEAT GRINDING
Reconditioning the valve seats is very important,
because the seating of the valves must be perfect for
the engine to deliver the power and performance it was
designed to produce.
Another important factor is the cooling of the valve
head. Good contact between each valve and its seat
ensures that heat will be carried away properly.
Several different types of equipment are available for
resurfacing valve seats. Carefully follow the recommen­
dations of the manufacturer of the equipment being
used to attain proper results.
Regardless of what type of equipment is used, it is
essential that valve guide bores be free from carbon or
dirt to ensure proper centering of the pilot in the guide.
Refer to "Specifications” in the proper section for valve
seat angle specifications.
NOTICE: Valve seats on 5.0L (exhaust only),
and 5.7L L.D.(exhaust only) are induction
hardened. The 5.7L H.D. and the 7.4L engines
use hardened seat inserts (exhaust only).
Excessive removal of stock may result in
damage to the valve seats.
REAMING VALVE GUIDES
The valve guides used in engines covered by this
manual are simply holes bored into the cylinder head
except on the 5.7L H.D. and 7.4L engines. The 5.7L
H.D. (exhaust valve only) and 7.4L engines (intake and
exhaust valves) use separate pressed-in valve guides
and are servicable. The valve guides used in all other
engines covered by this manual not replaceable.
If the valve stem to bore clearance as measured pre­
viously is excessive, the valve guides should be
reamed and a valve with an oversize stem installed.
Available oversize valves are as follows. Nominal
dimensions are given.
• 2.2L:
— Intake: 0.08 mm (0.003 inch), 0.13 mm (0.005
inch).
— Exhaust: 0.08 mm (0.003 inch).
• 4.3L H.D., 5.7L H.D.:
— Intake: 0.08 mm (0.003 inch), 0.38 mm (0.015
inch), 0.76 mm (0.030 inch).
— Exhaust: 0.08 mm (0.003 inch), 0.38 mm (0.015
inch).
Select a reamer that will provide a straight, clean
bore through the guide’s entire length (figure 25).
Reamer availability is as follows. Sizes given are
nominal.
• All engines except 7.4L:
— J 5830-1: 0.08 mm (0.003 inch) oversize.
— J 6621: 0.13 mm (0.005 inch) oversize.
— J 5830-2: 0.38 mm (0.015 inch) oversize.
— J 5830-3: 0.76 mm (0.030 inch) oversize.
— These reamers (except J 6621) also available
in Reamer Set J 5830-02.