Repair; Discharge Valves, Valve Stops, And Seats - GMC C Series 1993 Repair Manual

D. Install the connecting rod caps (35) and bolts
(36).
Tighten
• Bolts to 15 N m (11 ft. lbs.)
V
Important
• Do not move the connecting rod or crankcase
to avoid a false reading.
E. Check the measurement on the gaging material
scale (figure 13).
F. Replace the bearing inserts if the clearance is
excessive or the bearings are cracked or flaked.
• Position the caps to locate the locking slots
next to the same bolt.
9
Important
• DO NOT file or lap bearing caps or rods to take
up clearance. Use new bearing inserts if clear­
ances are excessive.
8. Pistons (26) and piston rings.
• Replace any piston that is scored, cracked, or
has enlarged ring grooves.
• Measure each piston with a micrometer in rela­
tion to the cylinder bore diameter (figure 14).
• Check the fit of the piston pins to the pistons
and connecting rod bushings. Refer to "Specifi­
cations" for clearance. If the fit is loose, replace
the piston and pin assembly.
: • Check the fit of the piston pin in the connecting
rod bushing by rocking the piston.
— If clearance is found, replace the rod and
bushing assembly.
• Check the fit of the piston rings in the piston
ring grooves. Refer to "Specifications,"
• Measure the gap and groove clearance with the
rings installed on the piston (figures 15 and 16),

REPAIR

DISCHARGE VALVES, VALVE STOPS, AND SEATS

• Lap slightly worn discharge valve seats with a lap­
ping stone, grinding compound, and grinding tool.
• Install new valve springs, valves, and discharge
valve seats.
• Maintain valve travel between 0.030 to 0.046 inch.
Figure 14— Measuring the Piston Diameter
AIR COMPRESSOR AND GOVERNOR 5J-7
Figure 15—Measuring the Piston Ring Gap
:
Figure 16—Measuring the Ring-to-Piston Clearance
To test for leakage, apply a water and soap solution
and 338 kPa (100 psi) of air to the cylinder head dis­
charge valve and seats. Leakage in the form of soap :
bubbles is permissible.
If excessive leakage is found, leave the air pressure
applied and with a fiber or hardwood dowel and a ham­
mer, tap the discharge valves off their seats to reduce
the leakage. With the air pressure still applied, check
for leakage around the discharge valve stop on the top ■
of the cylinder head casting. No leakage is permitted.-