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Camshaft vs. Crankshaft: What’s the Difference?

Camshafts in an engine

When you’re first learning about your vehicle’s engine, the terms “camshaft” and “crankshaft” could be confusing. The words sound similar, and they’re both located inside the motor. Although these shafts both need to spin for your vehicle to accelerate, they each perform a different function. Let’s take a look at the role of a camshaft vs. crankshaft inside an automotive engine.

The Camshaft: Breathing in and Out

Your engine’s pistons move up and down inside its cylinders when fuel and air are mixed together and then ignited by a spark plug. For that process to occur, valves at the top of the cylinders need to open and close to let in oxygen and expel the exhaust gases produced by the explosion.

The camshaft is responsible for opening each cylinder’s valves at the correct moment and ensuring they stay open for the appropriate time length. The shaft features “lobes” or “cams” that push against rocker arms while the camshaft rotates. This rotation raises the outside of the rocker arm, allowing the inside to press on the valve and open it. As the camshaft keeps rotating, the rocker arm returns to its original position, releasing its pressure on the valve, and the valve spring closes the valve. This is timed perfectly with the vehicle’s ignition to ensure that everything runs smoothly and produces power as efficiently as possible.

Camshafts are driven by a belt, chain or gear set. Some engines push the camshafts from below, while others sit on top of the motor and work from “overhead.” The latter design might feature a pair of camshafts. It’s also possible to vary the timing of when the valves are open on certain cam designs. Using a series of computer controls, this can create different power profiles at different engine speeds.

The Crankshaft: Putting the Power DownCrankshaft

A crankshaft translates the up-and-down motion of the engine’s pistons into rotation, so that the motor’s power is sent to the vehicle’s transmission and ultimately to the drive shaft(s). Each piston is connected to the crankshaft with connecting rods. These rods spin the shaft as they move up and down, while the rods and the shaft are rotated around bearings. Cranks are heavy, balanced components designed to withstand substantial forces at various engine speeds.

Camshaft vs. Crankshaft: Both Are Important

It’s not a question of whether a camshaft or crankshaft is more important than the other — each part is vital to how your engine functions. With regular maintenance such as oil changes, you shouldn’t have to replace either one until you reach over hundreds of thousands of miles.

Check out all the engine parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on a camshaft vs. crankshaft, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Pixabay.

Benjamin Hunting View All

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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