Most drivers know that the drive belts can be the cause of poor accessory performance and noise, but what many don’t realize is that the pulleys that contact the belt can often be the underlying cause of these malfunctions. Modern serpentine belts are part of a sophisticated accessory drive system, and each part of that system must work properly in order for the accessories to deliver peak performance and quiet operation.

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In a typical serpentine belt accessory drive system there is a drive pulley that is part of or attached to the crankshaft mounted harmonic balancer, a pulley at each of the belt-driven accessories, a belt tensioner and one or more idler pulleys. The rubber ring between the hub and inertia ring on the harmonic balancer can fail and these components are discussed more in depth on our Harmonic Balancers product page.

The pulleys that directly affect belt adjustment and noise are the tensioner and idler pulleys. A worn tensioner will cause the belt to slip and reduce accessory efficiency. For example, alternator charging output may be reduced which may wear the battery down. Your vehicle may not start and the CHECK ENGINE light may illuminate. Slippage will also wear the belt and cause a squealing noise, as well as generate heat that will reduce the life of accessory pulley bearings. Many tensioners also include a dampening mechanism to control vibration. A worn damper will allow belt slap, which can also cause pulley bearings to fail.

Pulley misalignment can cause belt chirp. Worn tensioner and idler pulleys can cause misalignment, which can also create excessive heat that wears the belt and the pulley bearings. Spraying water on the rib side of a serpentine belt can help determine whether a noise is a chirp or squeal. If the noise temporarily subsides, it’s a chirp caused by misalignment. If it gets louder, it’s a squeal caused by reduced belt tension. But you won’t have to make such distinctions if you replace the automatic tensioner and idler pulley(s) along with the serpentine belt - our accessory drive belt kits provide everything needed.

During deceleration, the spinning alternator creates drag, creating strain on the serpentine belt and tensioner. Many manufacturers use alternator decoupler pulleys, which allow the alternator to freewheel during deceleration, eliminating strain and increasing belt and tensioner lifespan. There are One-Way Clutch (OWC) and Overrunning Alternator Decoupler (OAD) pulleys. Both function similarly, but the OAD also contains a mechanism to reduce vibration. Many OE dealers do not service these pulleys separately from the alternator, but we have them, along with the installation tools, so you can save money.

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Engine Pulleys Reviews

Average rating:  5  4.8 - 16 reviews
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4.5 of 5
Timing Belt
Installation went as planned. Parts fit well and seem to be of high quality.
RPosted by Ron (Middleburg, VA) /
2009 Acura TL
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