What Is a Crankshaft Pulley?

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  • Written By: Lori Kilchermann
  • Edited By: Lauren Fritsky
  • Last Modified Date: 10 October 2019
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The crankshaft pulley is attached to the engine's harmonic balancer and drives the engine's accessories through the use of a rubber belt or system of belts, depending on the year and type of vehicle in question. Prior to the mid-1980s, most vehicles manufactured worldwide used a system of V-belts to drive an engine's component accessories. Since then, a single belt known as a serpentine belt has been driven by the crankshaft pulley and directed power to all systems in the engine compartment. While a serpentine-type crankshaft pulley is manufactured with a surface capable of driving the single belt, a V-belt system uses a crank pulley capable of driving from one to four V-belts.

The standard automotive engine is equipped with belt-driven features to provide charging for the electrical system, coolant circulation for the engine and heating system and hydraulic pressure for the power steering system. Optional belt-driven components are the air conditioning compressor and heavy hydraulic pumps for pickup trucks and tow vehicles as well as supercharger units for high-performance vehicles. All of these components are driven off of the crankshaft pulley. Some vehicles also use the crankshaft pulley to trigger the ignition system with flying magnets mounted on or in the pulley.


The engine's crankshaft is made of very heavy cast iron in most cases and solid steel in very high-performance engines. The crankshaft's snout must be made very strong to withstand the stress of placing the crankshaft pulley and the stress created from driving all of the components off of that single pulley. If the crankshaft pulley were allowed to wobble, the belts or belts would be easily thrown off of the pulley and the components depending on the drive power of the pulley would fail. Fortunately, the factory-stock fasteners and thread-locking liquids are commonly fail-proof and the crankshaft pulley typically remains tightened and in place for the entire life of the vehicle.

While the crankshaft pulley spins at revolutions equal to that of the operating engine, the various belt-driven components are turning at speeds much faster in most cases than the engine speed. This is accomplished by alternating the various pulley sizes with different-sized pulleys to change the final drive ratio to a more productive component drive speed. By placing a variety of different-sized pulleys on the engine components, each component can turn at a different speed all while being turned by the same drive pulley on the crankshaft.


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