Honing; Piston And Connecting Rod A S S E M B Lie S - GMC 1989 Light Duty Truck Repair Manual

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 manufacturer of
the equipm ent being used should be carefully
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
operation m ust be done ca re fu lly so th at 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
information.

HONING

1. When the cylinders are to be honed, follow the hone
m anufacturer's recommendations 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 during 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 eliminate 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.
NOTICE: H andle the pistons w ith care an d do
not a tte m p t to force them through the cylin der
u ntil the cylinder has been h o n e d to the co rrect
size as the piston can be d isto rted 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.
GENERAL ENGINE MECHANICAL 6A-5
6. By measuring the piston to be installed at the sizing
7. It is of the greatest im portance that refinished
8. Refer to " Specifications" in the proper section for
9. After final honing and before the piston is checked
fo r a d d itio n a l
10. Permanently mark the piston for the cylinder to
11. Apply clean engine oil to each bore to prevent
PISTON AND CONNECTING ROD
DISASSEMBLY (ALL EXCEPT 6.2 L ENGINES)
1. Piston rings. Use J 25220 (or equivalent) (figure 5).
2. Connecting rod bearing inserts. If the inserts are to
3. Piston pin (figure 6).
DISASSEMBLY (6.2 L ENGINES)
*
1. Piston rings. Use J 25220 (figure 5).
point specified in the proper section, and adding the
average of the clearance specification, the finish
hone cylinder measurement can be determined. It is
im p o rta n t th a t both the b lo ck and piston be
measured at normal room temperature.
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.
piston to bore clearance tolerances.
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
contaminated oil. After washing, the dry bore should
then be brushed clean with a power-driven fiber
brush.
which it has been fitted.
rusting.
ASSEMBLIES
Rem ove or D isconnect (Figures 4, 5 and 6)
Tools Required
J 25220 Ring Expander (or equivalent)
J 24086 Piston Pin Remover
and Installer
In most cases the rings should be discarded and
replaced with new ones at assembly.
be reused, place them in a rack so they may be
reinstalled in their original connecting rod and cap.
• 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.
Disassem ble (Figures 5 and 7)
Tool Required:
J 25220 Ring Expander (or equivalent)
by th e