The overview of Auxiliary Idler Pulleys

There are two different belt systems on the cars: V-Belt systems and Timing Belt Systems. The auxiliary idler pulleys are found on the V-Belt systems, which has a role to power a variety of important components such as alternator, power steering pump, air-con pump and water pump. The auxiliary V-Belts (also called as Serpentine belts or Poly-V Belts) may vary in length but typically they are quite long. This requires the system to be supported with idler pulleys to reduce the tension and ensure the optimum tightness. The whole system looks like a V letter, thus the name.


If the belt flexes by more than inch then it may need to be tightened or the tensioner may be the cause of the issue. If the pulleys have cracks, nicks or any type of distortion it can cause V-ribbed belt to make noise.

What are Timing Idler Pulleys?

As mentioned on the first paragraph, the other system that the car has is the Timing Belt System. This system uses a Timing Belt. This system is used to operate the rotation of the crankshaft and the camshaft at the same time. Here the type of idler pulley to use in this system is called timing idler pulley. Depending on the engine, there may be multiple timing idler pulleys to help support the timing belt and its function.

How to differentiate the two systems?

The way to understand the systems is to look at the inner face of the belts. The V-Belts have an unbroken pattern of lines that follows a horizontal path. On the contrary, the Timing Belts have multiple canals that go vertical throughout the belt’s inner surface. These are called rubber ribs.

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