Cylinder Bores; Piston And Connecting Rod Assemblies; Piston Selection - GMC 1989 Light Duty Truck Repair Manual

Figure 22—Checking the Block Gasket 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 the block.

CYLINDER BORES

For information regarding cylinder bore measuring and
r e c o n d itio n in g , re fe r
MECHANICAL (SEC. 6A).
PISTON AND CONNECTING ROD
ASSEMBLIES
For information regarding disassembly, cleaning and
inspection and assembly of piston and connecting rod
assemblies, refer to GENERAL ENGINE MECHANICAL
(SEC. 6A).
For piston selection in fo rm a tio n , refer to " Piston
Selection" in this section.

PISTON SELECTION

In order to select the proper piston for each bore, it is
necessary to measure the outside diameter of the piston
and the inside diameter of the bore. Once the diameters
have been measured, the difference between the bore
diameter and the piston diameter will be the piston to bore
clearance.
1. Check the used piston to cylinder bore clearance.
M easure (Figures 23 and 24)
Cylinder bore diameter using a telescoping
bore gage. Measure the bore parallel to the
crankshaft at the gaging point which is 57.15
mm (2.25-inch) from the top of the cylinder
bore. By measuring at this point, the smallest
bore diameter will be obtained.
Piston diameter with a micrometer. Measure
the piston skirt at a right angle to the piston
pin, at the centerline of the piston pin, which is
to G E N E R A L E N G IN E
2.5 LITER L4 ENGINE 6A1-15
A. Bore G a g in g P oint
B. P isto n G a g in g P oint
Figure 23— Measuring the Piston Diameter
46.037 mm (1 13/ie-inch) from the piston crown.
By measuring at this point, the largest piston
diameter will be obtained.
• Subtract the piston diameter from the cylinder
bore diameter to determine the piston to bore
clearance.
• Refer to " Specifications" at the end of this
section to determine if the piston clearance is
in the acceptable range.
2. If the used piston is not acceptable, determine if a
new piston can fit the cylinder bore.
3. If a new piston does not bring the clearance within
tolerances, the cylinder bore must be reconditioned.
4. Mark the piston to identify the cylinder for which it
was fitted.
Figure 2 4 — M easuring C ylinder Bore D iam eter
F-01996
A. 2 1 /4-inch
B. C y lin d e r Bore
F-01997