CTS 2003-2005

Pistons & Connecting Rods


None of the engines covered by this manual use pistons with wrist pins retained by any type of clip. Press fit pistons require special presses and/or heaters to remove/install the connecting rod and this operation should only be performed by a machine shop.

All pistons will have a mark indicating the direction to the front of the engine and the must be installed into the engine in that manner. Usually it is a notch or arrow on the top of the piston, or it may be the letter F cast or stamped into the piston. This is important because pistons aren't exactly round; they are made slightly oval, or barrel shape. The reason for this is that the piston's shape changes slightly under the heat and stress of engine operation. Too, the loads on the piston are not uniform. So the piston is designed with a slight offset and in a shape that works best when the engine is running. This reduces running friction and a cold-start noise called "piston slap." The pistons absolutely must be installed in the proper orientation or you will fail the engine.

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Fig. Most pistons are marked to indicate positioning in the engine (usually a mark means the side facing the front)

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Fig. Always keep the connecting rod and caps in matching sets. Never mix connecting rod caps or the engine will fail

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Fig. This type of special tooling fixture is what the factory recommends to remove a piston wrist pin

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Fig. This type of special tooling fixture is what the factory recommends to install a piston wrist pin. Automotive machine shops can do the job quickly and inexpensively

Cleaning & Inspection

Connecting Rods

You should have the connecting rod checked for straightness at a machine shop. If the connecting rod is bent, it will unevenly wear the bearing and piston, as well as place greater stress on these components. Any bent or twisted connecting rods 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 by a machine shop.

You can also use Plastigage® to check the bearing clearances. The assembling section has complete instructions on its use.


The piston should be visually inspected for any signs of cracking or burning (caused by hot spots or detonation), and scuffing or excessive wear on the skirts. The wrist pin attaches the piston to the connecting rod. The piston should move freely on the wrist pin, both sliding and pivoting. 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 pin. If there are C-clips retaining the pin in the piston then you have wrist pin bushings in the rods. There should not be any excessive play between the wrist pin and the rod bushing. Normal clearance for the wrist pin is approx. 0.001-0.002 in. (0.025mm-0.051mm).

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Fig. Measure the piston's outer diameter, perpendicular to the wrist pin, with a micrometer

Use a micrometer and measure the diameter of the piston, perpendicular to the wrist pin, on the skirt. Compare the reading to its original 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, but the bore is not, you will need a new piston. If both are out of specification, you will need the cylinder bored and oversize pistons installed. Generally if two or more pistons/bores are out of specification, it is best to bore the entire block and purchase a complete set of oversize pistons.