Can you rebuild a piston rod in a car engine?

Yes, but... A car engine has more than one piston rod, and to get to them you have to disassemble the entire engine. As long as you are at it, rebuild all of them. Here is how: Remove wrist pins from the pistons. The rods will come off. Remove the bearings from the rods and cap. Keep the caps with their respective rods. DO NOT CROSS-MIX THEM. Re-torque the bearing caps onto the ends of the rods. Re-bore the holes. This is best done by a professional machine shop. Buy new (oversized) bearings to put in the oversized holes. The size difference is a matter of a few thousandths of an inch, so you will need a good set of calipers to measure. As long as you are at it, hone out the cylinders and buy new piston rings. Also replace the crank journal bearings in the engine block. Voila. New engine.