Cleaning, Inspection, And Repair; Main Bearing Cap R Eplacem Ent - GMC 1989 Light Duty Truck Repair Manual

6A4-14 4.8 LITER L6

CLEANING, INSPECTION, AND REPAIR

A solvent tank, large enough to hold the larger engine
parts, will be needed along with various bristle brushes
and a gasket scraper. A source of compressed air will be
helpful in the cleaning operations.
Precision measuring tools will be required for the in­
spection procedure. These include: micrometers, cylinder
bore gage, feeler gages, dial indicator set, etc. The in­
spection work, performed with the proper method and
tools, is most important. The rebuilt engine cannot be ex­
pected to perform properly if parts worn beyond accepta­
ble limits are reused.
BLOCK
Clean (Figure 5)
1. Block (115) in solvent.
2. Block gasket surfaces.
3. Cylinder bores.
4. Oil galleries and passages.
5. Scale deposits from the coolant passages.
Inspect (Figure 5)
I f '
1. All expansion plugs for looseness or leakage.
2. Valve lifter bores for deep scratches and varnish
deposits.
3. Block (115) for cracks, especially in the following
areas:
— Cylinder walls. *
— Coolant jackets.
— Main bearing webs.
— Engine mount bosses.
4. Main bearing bores and main bearing caps (137 and
152).
— All main bearing bores should be round and
uniform in ID at all bearing supports.
L
93. Screw
94. Camshaft Gear
Figure 23— Camshaft Thrust Plate Screws
The area where the main bearing inserts (130,
133, 136, and 153) contact the main bearing
bore should be smooth.
If a main bearing cap is damaged and requires
replacement, replace it as outlined later in this
section.
t j j M easure (Figure 24)
Head gasket surface distortion. Use a straight edge
and feeler gage to check for flatness of the milled
surface at the top of the cylinder block. The surface
must be flat (within 0.10 mm [0.004-inch]) to assure
that the gasket will provide a tight seal between the
cylinder head and block.
MAIN BEARING CAP
REPLACEMENT
-►+ Install or C onnect (Figure 5)
1. New main bearing cap (137 or 152). The arrow on
the main bearing cap faces the front of the engine
(opposite the flywheel).
2. Bolts (138) and stud (139).
Tighten
• Bolts (138) and stud (139) to 90 N m (65 ft.
lbs.).
M easure (Figure 25)
Main bearing vertical ID (inside diameter). Use an
inside micrometer.
• This dimension should be the same as the
other main bearing bore vertical diameters.
• If it is necessary to increase the vertical ID,
use an equal thickness of special service
bearing cap shims at each side of the cap to
B-05068