Crankshaft; Piston & Connecting Rods; Pressed-On Pistons - Chevrolet Trailblazer Service Manual

reflect the most wear. This is where the greatest force is exerted on the cylinder as the
piston is forced down during combustion. This is known as thrust wear. Take the top, 90
degree measurement and compare it to the bottom, 90 degree measurement. The
difference between them is the cylinder taper. The amount of cylinder wall wear is always
greater at the top of the cylinder than at the bottom. Any cylinder that has a taper of 0.0012
in. (0.305 mm) or more must be re-bored.
Compare the cylinder bore measurements to the size of the pistons to determine piston-to-
wall clearance.

Crankshaft

Inspect the crankshaft for visible signs of wear or damage. All of the journals (piston and
main bearing) should be perfectly round and smooth. Slight scores are normal for a used
crankshaft, but should hardly be felt with a fingernail. Make the crankshaft measurements
with a micrometer at the front and rear of each journal (x). Turn the micrometer 90 degrees
and take two more readings (y), front and rear. The difference between the x and y reading
is the out-of-round measurement. Generally, there should be no taper or out-of-roundness
found. A difference up to 0.0005 in. (0.0127mm) for taper or out-of roundness is
acceptable. All measurements should be within the factory specifications for journal
diameters.
If the crankshaft journals are within specifications, it is recommended that they be polished
before being reusing the crankshaft. Polishing the crankshaft ensures that any minor burrs
or scoring are smoothed, thereby reducing the chance of scoring the new crankshaft
bearings.
Pistons & Connecting Rods

Pressed-On Pistons

The piston should be visually inspected for any signs of cracking or burning (caused by hot
spots or detonation), scuffing or excessive wear on the skirts. The piston should move
freely on the wrist pin, It should slide and pivot freely. Grasp the connecting rod securely,
or mount it in a vise, and try to rock the piston back and forth along the centerline of the
wrist pin. There should not be any excessive play evident between the piston and the wrist
pin. If C-clips retain the pin in the piston then the piston may be equipped with wrist pin
bushings in the connecting rod. There should not be any excessive play between the wrist
pin and the rod bushing. Normal wrist pin clearance is approx. 0.001 - 0.002 in. (0.025-
0.051 mm). Check the manufacturer's specifications for the exact values.