GMC 1989 Light Duty Truck, Repair Manual, Page: 339 / 998

GENERAL ENGINE MECHANICAL 6A-5
boring bar may be tilted which would result in the
rebored cylinder wall not being at right angles to the
crankshaft.
3. The instructions furnished by the m anufacturer of
the e qu ip m en t being used should be ca re fully
followed.
4. When reboring cylinders, all crankshaft bearing
caps must be in place and tightened to the proper
torque to avoid d istortion of bores in the final
assembly. Always be sure the crankshaft is out of
the way of the boring cutter when boring each
cylinder. C rankshaft bearings and other internal
parts must be covered or taped to protect them
during the boring or honing operation.
5. When taking the final cut with a boring bar, leave
0.03 mm (0.001-inch) on the diam eter for finish
honing to give the required position to the cylinder
clearance specifications. (The honing or boring
o pe ra tion m ust be done c a re fu lly so th a t the
specified clearance between pistons, rings, and
cylinder bores is maintained.)
Im portant
• R e fe r to th e p ro p e r s e c tio n fo r a d d itio n a l
information.
HONING
1. When the cylinders are to be honed, follow the hone
m anufacturer’s recomm endations for the use of the
hone and cleaning and lubrication during honing.
Use only clean, sharp stones of the proper grade for
the amount of material to be removed. Dull, dirty
stones cut unevenly and generate excessive heat.
When using coarse or medium grade stones use
care to leave sufficient metal so that all stone marks
may be removed with the fine stones used for
finishing to provide proper clearance.
2. O ccasionally d uring the honing operation, the
cylinder bore should be thoroughly cleaned and the
piston selected for the individual cylinder check for
correct fit.
3. When honing to elim inate taper in the cylinder, full
strokes of the hone in the cylinder should be made
in addition to checking measurement at the top,
middle and bottom of the bore repeatedly.
NO TIC E: H andle the p isto n s w ith care an d do
no t a tte m p t to force them through the cy lin d e r
u n til the cylin der has b e e n h o n e d to the co rre c t
size as the piston can b e d is to rte d through
careless handling.
4. When finish honing a cylinder bore to fit a piston,
the hone should be moved up and down at a
sufficient speed to obtain very fine uniform surface
finish marks in a cross-hatch pattern of the specified
angle.
• 2.5 L: 45 degrees
• 2.8 L: 20 to 32 degrees
• All others: 45 to 65 degrees
5. The finish marks should be clean but not sharp, free
from imbedded particles and torn or folded metal.
6. By measuring the piston to be installed at the sizing
point specified in the proper section, and adding the
average of the clearance specification, the finish
hone cylinder m easurement can be determined. It is
im p o rta n t th a t both the b lo c k and p iston be
measured at normal room temperature.
7. It is of the greatest im portance that refinished
cylinder bores are trued up to have the less than the
specified out-of-round or taper. Each bore must be
final honed to remove all stone or cutter marks and
provide a smooth surface.
8. Refer to “ Specifications” in the proper section for
piston to bore clearance tolerances.
9. After final honing and before the piston is checked
for fit, clean the bores with hot water and detergent.
Scrub with a stiff bristle brush and rinse thoroughly
with hot water. It is essential that a good cleaning
operation be perform ed. If any of the abrasive
material is allowed to remain in the cylinder bores, it
will wear the new rings and cylind er bores in
a d d itio n to th e b e a rin g s lu b ric a te d by th e
contaminated oil. After washing, the dry bore should
then be brushed clean with a power-driven fiber
brush.
10. Permanently mark the piston for the cylinder to
which it has been fitted.
11. Apply clean engine oil to each bore to prevent
rusting.
PISTON AND CONNECTING ROD
ASSEMBLIES
DISASSEMBLY (ALL EXCEPT 6.2 L ENGINES)
R em ove or D isco n n ect (Figures 4, 5 and 6)
Tools Required
J 25220 Ring Expander (or equivalent)
J 24086 Piston Pin Remover
and Installer
1. Piston rings. Use J 25220 (or equivalent) (figure 5).
In most cases the rings should be discarded and
replaced with new ones at assembly.
2. Connecting rod bearing inserts. If the inserts are to
be reused, place them in a rack so they may be
reinstalled in their original connecting rod and cap.
3. Piston pin (figure 6).
• Place the piston/connecting rod on support
fixture J 24086-20. Make sure the connecting
rod is fully supported. Use J 24086-900 and
J 24086-280 for 2.8 L pistons.
• Place remover J 24086-8 (J 24086-88A for
2.8 L pistons) on the support fixture.
• Press out the piston pin.
DISASSEMBLY (6.2 L ENGINES)
D isassem ble (Figures 5 and 7)
*
Tool Required:
J 25220 Ring Expander (or equivalent)
1. Piston rings. Use J 25220 (figure 5).