What is a Piston Pin?

Lori Kilchermann

A piston pin, also known as a wrist pin, is a hardened steel pin which connects an engine's piston to a connecting rod. This pin is hollow to reduce weight and is held in place with a number of different methods. Most factory-stock piston pin designs rely on a pressed fit with the pin being pressed into the connecting rod. High-performance pistons are typically held in place with wire clips or aluminum buttons.

Inside the cylinder-shaped pistons at top are horizontal pins that lock in the vertical connecting rods, which turn the crankshaft at bottom.
Inside the cylinder-shaped pistons at top are horizontal pins that lock in the vertical connecting rods, which turn the crankshaft at bottom.

When installing a new piston pin it is imperative that the pin be oiled where it passes through the piston. Failure to adequately lubricate the pin will result in a seized piston nearly every time. The high heat generated by the connecting rod rotating within the piston causes a dry or inadequately lubricated pin to fall into the piston. This will cause the engine to lock up as the piston locks onto the pin. Broken connecting rods and even a broken engine block could also result.

While most stock piston pins are made of hardened steel, many high-performance applications utilize tool steel pins. These tool steel pins are the strongest and most durable available and can withstand ultra high horsepower. The use of high-quality materials also allows the tool steel piston pins to be made very light weight. This aids in the engine's ability to accelerate at a much faster rate than an equally prepared engine equipped with heavier pins.

While most pistons are sold complete with piston pins included, some of the highest-quality racing pistons are sold without pins. This allows the engine builder to purchase the pin package which best suits the engine's build characteristics. Nearly every professional engine builder around the world has a unique manner of assembling engines; most will agree, however, that full-floating pins are the correct call for a serious performance engine assembly.

In a stock engine, the piston pins are lubricated and cooled by oil which is splashed or thrown off of the crankshaft as it spins within the engine block. In most normal driving conditions, this is a successful design. In racing or high-performance applications, the engine builder will often incorporate a system of tubes directed toward the bottom of the pistons. These tubes spray oil directly onto the pins and the pin bosses, maintaining lubrication and cooling efforts. By keeping the piston pins cool, the pistons are able to generate maximum horsepower without heat-related engine failure.

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Discussion Comments


@aLFredo - I had the same thing happen, and my car was an older car as well. When my car had the issue with its piston pins, I went ahead and replaced the car. Since it was an older car, I thought going ahead and replacing it was the best course.

I hope you have better luck with your car!


A piston pin once landed me on the side of the road!

There was no need to use a piston pin removal tool to get it out of my car's engine! As my car threw a piston pin and stopped working, leaving me to coast to the side of the interstate. My mechanic told me, "Your car threw an engine rod."

I told him that I didn't know my car could throw. I would have been almost proud at my car's new trick if...it had been such an expensive new habit! It was an older car so I wonder if they use different pistons now.

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