Connecting Rod; Measuring The Piston's Outed Diameter - Chevrolet Trailblazer Service Manual

Measuring the piston's outer diameter
Use a micrometer and measure the outside diameter of the piston perpendicular to the
wrist pin at the skirt. Compare this measurement to the cylinder measurement obtained
earlier. The difference between the two readings is the piston-to-wall clearance. If the
clearance is within specifications, the piston may be used as is. If the piston is out of
specification and the bore is not, you will need a new piston. If both the piston and the bore
are out of specification, you will need the cylinder re-bored and an oversized piston.
Generally, if two or more pistons or bores are out of specification, it is best to re-bore the
entire block and install oversize pistons. If the pistons are worn, but the cylinders are
acceptable, one alternative is to use +0.005 inch oversize pistons and hone the cylinders
to the correct size.

Connecting Rod

Check the connecting rod for straightness. If the connecting rod is bent, it will unevenly
wear the bearing and piston, as well as place greater stress on these components. Any
connecting rods that are bent or twisted must be replaced. If the rods are straight and the
wrist pin clearance is within specifications, then only the bearing end of the rod need be
checked. Place the connecting rod into a vice, with the bearing inserts in place, install the
cap to the rod and torque the fasteners to specifications. Use a telescoping gauge and
carefully measure the inside diameter of the bearings. Compare this reading to the rods
original crankshaft journal diameter measurement. The difference is the oil clearance. If
the oil clearance is not within specifications, install new bearings in the rod and take
another measurement. If the clearance is still out of specifications, and the crankshaft is
not, the rod will need to be reconditioned or replaced.
NOTE: You can also use Plastigage® to check the bearing clearances.