How to Loosen a Tensioner Pulley

engine pulley, water pump, and alternator, but no drive belts to drive them!
Without Drive Belts and a Belt Tensioner, these Pulleys Aren't Going Anywhere!.

For decades, drive belts, V-belts, multi-vee-belts, and serpentine belts have been used to transmit power from the engine crankshaft pulley to accessories, such as the power steering pump, air conditioning compressor, water pump, or cooling fans. Toothed timing belts and timing chains, too, are used to transmit power from the crankshaft to the camshafts, and some from the camshaft to camshaft, depending on engine design.

The drive belt, timing belt, or timing chain will not work well, or for very long, if at all, with incorrect tension. A loose drive belt won’t drive the accessory reliably, slipping and making noise. A loose timing belt or timing chain could lead to excessive noise, abnormal wear, or crankshaft/camshaft correlation problems—DTC P0016 is a classic example of a skipped timing tooth. Conversely, an excessively tight belt may cause accessory or pulley bearing damage. Various forms of tensioner pulley maintain long-term engine and accessory quietness and reliability.

Tightening or Loosening

Sometimes, maintenance or repair will require tightening or loosening a tensioner pulley. Replacing a drive belt or timing belt, for example, would require you to loosen a tensioner pulley to make room for the new belt, as the new belt is smaller than the worn drive belt.

You'll need to tighten a tensioner pulley, in most cases, after the installation of a new drive belt, or to adjust for a stretched drive belt that hasn’t worn enough to warrant replacement. Stretch belts don’t need tensioner pulleys but are “stretched” into place using a special tool—always use the special tool to prevent belt damage.

Tensioner pulleys generally fall into two categories: accessory-integrated (AI) and non-accessory-integrated (NAI). Think of AI tensioners as adjustable accessories, such as an alternator, and NAI tensioners as adjustable idler pulleys. There are three types of tensioner pulleys and several ways to loosen them. What follows are some general guidelines, but always check your repair manual or owners manual for information and steps specific to your vehicle.

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Mechanical Tensioner Pulley

mechanical belt tensioner mounted on an alternator on a custom engine
This Belt Tensioner Moves the Alternator Position to Apply Tension to the Drive Belt.

Mechanical tensioner pulleys are the simplest, most common, and least prone to failure. There is one caveat, however, as mechanical tensioner pulleys require manual adjustment. This makes them prone to user error, resulting in insufficient or excessive belt tension. Additionally, they need to be adjusted to compensate for belt stretch over time.

Mechanical tensioner pulleys are generally adjusted using a sliding bolt, usually AI tensioners, or by adjusting a tensioner screw, usually NAI tensioners. The tiny Honda timing belt tensioner spring pictured in this section is more of a reference than a tensioner, making it an NAI mechanical tensioner, adjusted by hex key and torqued.

The Steps

To loosen an AI tensioner, such as an alternator, loosen the main mounting bolt, usually on the engine, and the locking bolt, usually on a bracket or arm. If equipped with a tensioner screw, back off the tensioner screw. Then, push the alternator toward the other pulleys, loosening the belt.

To loosen an NAI tensioner, loosen the locking nut or bolt, then back off the tensioner screw. Push the pulley toward the other pulleys or accessories, loosening the belt.

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Spring Tensioner Pulley

spring belt tensioner and serpentine belt
This Spring Tensioner Pulley Keeps Constant Tension on the Serpentine Belt, Self-Adjusting for Stretch and Wear.

Spring tensioner pulleys, as the name implies, use a spring to hold tension on the belt. Most, if not all, spring tensioner pulleys are NAI tensioners and include a hydraulic damper. They are more complex and expensive but don’t require adjustments and are less prone to user error.

The spring maintains tension, while the hydraulic damper keeps it from bouncing under load changes. This prevents timing belts and timing chains slapping and jumping teeth and keeps drive belts from slipping and making noise. To loosen a drive belt spring tensioner pulley, refer first to the repair manual or owners manual’s specific year, make, and model information.

The Steps

You may need a special tool, but many spring tensioners have a square hole, for a 3/8” or 1/2” breaker bar, or a hex or square protrusion for a wrench or socket. Using the appropriate tool, release tension on the belt. You'll need to hold some spring tensioners while slipping on a new belt. Others may have a locking mechanism, such as a hole for a locking pin or hex key.

Toyota and other timing belt tensioners are loosened by simply removing them from the engine. You must slowly compress them in a bench vice and lock them with a pull-pin before reinstallation.

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Hydraulic Tensioner Pulley

hydraulic tensioner on a timing chain slipper
This Hydraulic Timing Chain Tensioner is Powered by the Oil Pump.

Hydraulic (not hydraulic-damped) tensioners are almost always located in the timing case, mostly on vehicles with timing chains, though some are used with timing belts. Hydraulic tensioners are powered by oil pressure from the engine oil pump and may press on a tensioner pulley (timing belts) or tension slipper (timing chain). You'll likely need the year, make, and model information, and you may have to use special tools for this kind of tensioner pulley.

The Steps

Typically, a hydraulic tensioner needs to be “reset” and locked after removing it from the engine. Remove the lock only after the tensioner, pulley, or slipper, and timing belt or timing chain are installed and aligned.

The next time you work with a drive belt, timing belt, or timing chain, you’ll likely have to loosen a tensioner pulley to remove it. Following these general guidelines and specific instructions from your owners manual or repair manual, your belt or chain will function for the life of your car.