Cylinder Head; Disassembly; Cleaning And In Sp Ectio - GMC 1990 Light Truck Repair Manual

6A-16 GENERAL ENGINE MECHANICAL
Figure 29—Testing the Hydraulic Lifter —
Flat Type Only
2. Swing the weight arm out of the way, raise the arm,
and position the lifter into the boss in the center of
the tester cup.

DISASSEMBLY

*
Disassemble
Valves and components. Refer to the proper section.
CLEANING AND INSPECTION
g i
Clean (Figures 30 and 31)
Tools Required:
J 8089 Wire Brush
J 8101 Valve Guide Cleaning Tool
Carbon from the combustion chambers. Use J 8089
(figure 30).
Valve guides. Use J 8101 (figure 31).
Valve stems and heads on a wire wheel.
Carbon and old gasket from the cylinder head
gasket surface.
Inspect
— Cylinder head for cracks in the exhaust ports,
combustion chambers, or external cracks to the
coolant chamber. Gasket surfaces should be free of
damage.
— Valves for burning, pitting, or warpage. Grind or
replace as needed. Refer to " Valve Grinding."
Check the valve stems for scoring or excessive
wear. Stems must not be bent.
3. Adjust the ram (with the weight arm clear of the ram)
so that the point is positioned on the set line
(marked " S" ). Tighten the jam nut to maintain the
setting.
4. Operate the lifter through full travel of the plunger by
pumping the weight arm to fill the lifter with test fluid
and force out air.
5. Raise the weight arm to allow the plunger spring to
expand fully; lower the arm onto the ram and
commence turning the crank slowly
every
6
Time indicator travel from the lower line (first line
.
above the set line) to the line marked 0.094 or
3 /32-inch, while rotating the cup with crank. The lifter
is satisfactory if the rate is between 12 and 90
seconds.

CYLINDER HEAD

— Rocker arm studs (if used) for wear, damage or
improper fit.
— Valve seats for pitting or other damage. Grind or
reface as needed.
— Rotators (if used). The rotators should rotate
smoothly, without bind.
t j j Measure (Figures 32, 33, and 34)
Tools Required:
Valve stem to guide bore clearance.
Important
• Lifter must be completely submerged at all
times.
• Continue pumping for several strokes after
definite resistance is felt.
2
seconds).
J 8001 Dial Indicator (or equivalent)
J 8056 Valve Spring Tester
• 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 engines smoothness.
• Clamp a Dial Indicator J 8001 (or equivalent)
on one side of the cylinder head rocker arm
cover gasket rail (figure 32).
• Locate the indicator so that 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.
• Drop the valve head about 1.6 mm (
off the valve seat.
(1
revolution
1
/ie-inch)