What’s a crank pulley?

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The crankshaft pulley drives engine accessories through a rubber belt or belt system. Most vehicles now use a serpentine belt, while older ones used a V-belt system. The pulley must be strong to withstand stress and prevent wobbling, which could cause failure of belt-driven components. Different sized pulleys are used to change the final drive ratio and allow components to rotate at different speeds.

The crankshaft pulley is attached to the engine’s harmonic balancer and drives engine accessories through the use of a rubber belt or belt system, depending on the year and type of vehicle in question. Prior to the mid-1980s, most vehicles manufactured around the world used a V-belt system to drive the components of an engine. Since then, a single belt known as a serpentine belt has been driven by the crankshaft pulley and has 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 crankshaft pulley capable of driving one to four V-belts.

The standard automotive engine is equipped with belt drive 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 include air conditioning compressor and heavy hydraulic pumps for pickup trucks and tow vehicles, as well as supercharging units for high-performance vehicles. All of these components are thrown off the crankshaft pulley. Some vehicles also use the crankshaft pulley to activate the ignition system with flying magnets mounted on or in the pulley.

The engine crankshaft is made of very heavy cast iron in most cases and solid steel in very high performance engines. The muzzle of the crankshaft must be made very strong to withstand the stress of fitting the crankshaft pulley and the stress created by driving out all the components on that single pulley. If the crankshaft pulley were allowed to wobble, the belts or belts would be easily thrown off the pulley and components that rely on the pulley’s driving power would fail. Fortunately, factory fasteners and thread-locking fluids are often fail-safe and the crankshaft pulley usually stays tight and in place for the life of the vehicle.

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

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