Hummer H1 Service Manual page 111

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2-74 Engine
ACCEPTABLE
CRACK LENGTH
NOT OVER
3/16" IN (5 MM)
Figure 2-138: Prechamber Inspection Points
Check fit of each pre-chamber in the cylinder head. Replace
loose (or cracked) chambers. Oversize chambers are available
when needed. The oversize parts are marked with ID code
"08." The code numerals appear on the chamber crown, side,
or interior (Figure 2-139)
.
Figure 2-139: Oversize Prechamber I.D.
Measure valve stem clearance with a dial indicator. Required
clearance is 0.001-0.003 in. (0.026-0.069 mm) for intake and
exhaust valves. If clearance is beyond limits, ream the valve
guide with reamer (Figure 2-140) and install new valve with
0.0035 in. (0.089 mm) larger stem.
REAMER
J–5830-1
Figure 2-140: Typical Method of Reaming
Valve Guides
A
B
UNACCEPTABLE
CRACK LENGTH
OVER 3/16" (5 MM)
A
A. HEAD GASKET
SEALING BEAD MARK
B
B. FIRE SLOT
S02-240
SIZE CODE
LOCATIONS
REAMER
HANDLE
Check the valve stems for wear, scoring, or distortion. Inspect
the faces for pitting, cracks, or burnt segments. Also inspect
the lock grooves at the stem top. Be sure the grooves are free of
cracks, worn or broken lands, or chipped spots. Replace any
valve exhibiting the foregoing conditions.
Grind the valve faces only lightly to obtain the required 45°
face angle (Figure 2-141). Take care to avoid cutting into the
valve margin. Quik Way, Van Norman, Sioux or similar qual-
ity equipment is recommended.
90°
D
A
A-SEAT WIDTH = INTAKE 0.035-0.060 in. (0.089-1.524 mm)
EXHAUST (0.060-0.093 in. (1.524-2.36 mm)
B-FACE ANGLE (INTAKE & EXHAUST) = 45°
C-SEAT ANGLE (INTAKE & EXHAUST) = 46°
D-VALVE FACE CONTACT AREA
Figure 2-141: Valve Refacing Angles and Widths
Grind the valve seats to the required 46° angle with the previ-
ously recommended equipment. Or, use a 4-6 blade carbide
cutter to dress the seat.
Lightly lap the valves and seats with a fine grit compound.
Clean the valves and seats and inspect the lap marks. The lap
marks, which represent the actual contact areas on the valves
and seats, should be concentric, and equal in width throughout.
Ideal seat width is 0.063 in. (1.6 mm).
If the lap marks are thick-thin or eccentric, the valves or guides
are worn beyond tolerance. Verify by rechecking valve stem
clearance and valve seat runout with a dial indicator.
®
C
B