What does the strain pulley do?
A drive belt tensioner is a pulley mounted on a spring mechanism or adjustable pivot point that can be used to keep tension on the engine belts. … Both are used to keeptension on the engine serpentine belts to ensure that they can travel the various engine accessories.

How do you modify a tensioner pulley?
Switch the adjustment bolt on the side, top or bottom level of the pulley counterclockwise with the ratchet and socket before item belt is loose enough to eliminate. Tighten the tensioner pulley by turning the adjustment bolt clockwise with the ratchet and socket before belt is tight.
How do you know

A tensioner pulley manuals the belt around the tensioner and allows the belt to spin as the tensioner maintains pressure against it. A failing tensioner pulley can cause power loss and damage to your belt-driven systems. You might have a failing tensioner pulley if you hear any squeaking or squealing under the hood. Bearings on the pulley can wear out, causing noise and warmth. Pulleys are usually manufactured from either plastic or metallic, so check the pulley itself for any damage aswell. At O’Reilly Auto Parts, we have tensioner pulleys available for many vehicle models.

The automatic pulley tensioner comes with an internal spring-loaded mechanism that keeps the serpentine belt under frequent tension. Its design permits it to keep carefully the serpentine belt taut, so that the other equipment pulleys rotate at the same rpm (revolutions each and every minute) while beneath the same safe pressure. Tensioner pulleys may also absorb slight shock loads that happen when the air conditioner cuts on / off. As a frequently rotating aspect, the pulley tensioner can give off some indicators before failure.

Rust and Corrosion
The pulley tensioner sits exposed to the elements at the front of the engine. Put through puddled water “splash-up,” as time passes the tensioner arm and pulley mechanism can rust. Corrosion can freeze the computerized tensioner device or corrode the shaft bearings, which will cause a frozen posture in the adjustment pressure. Without the correct stress, the belt can slip.
Debris Contamination
Rocks, gravel and other road debris can be thrown up into the tensioner pulley grooves and jam the device. This can permit the serpentine belt to slide on the tensioner pulley and lose. Overheated pulley temperatures results, and eventually the serpentine belt will melt and snap off.
Pulley Tensioner Spring
The pulley tensioner spring in the housing may become weak from age and repeated contact with heat. This causes the belt to flutter and skip instead of maintaining a constant strain on the pulley. Symptoms of a fragile spring display as glazing on the underside of the serpentine belt, with an occasional flickering of the dashboard’s charging mild indicator. Squealing or squeaking will always be heard at the belt area.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, it means the interior shaft bearings have worn. This may cause a pulley misalignment. Terrible bearings cause an audible growling sound. The outer ends of the serpentine belt will fray and extend the belt. Sooner or later the rubberized belt grooves flatten out and cause major slippage. An excessively wobbling pulley can throw the belt off, leading to all the add-ons to quit functioning.
Lever Arm Freeplay
Some tensioner pulleys have markings on the casing that indicate the utmost range that the pulley can travel. If the lever arm of the tensioner rides under or higher the designated mark, this implies a stretched belt or a lever arm which has jammed in one position.
Pulley Misaligment
The tensioner pulley face must match up to the other accessory pulleys with a parallel alignment. Placing a long, straightedge ruler against the face tension pulley 2of the tensioner pulley, and flushing it against another equipment pulley, can measure the angle. Any off-angle measurement indicates worn shaft bearings in the pulley housing.
Serpentine Belt Noise
A moderately put on serpentine belt gives off a constant squeaking noise during engine idle. Belts which have worn severely task a loud chirping or squealing sound. The cause factors to a glazed, donned or cracked belt. Dried out or partially frozen tensioner pulley bearings can cause such noises by deteriorating the belt prematurely.
Lever Arm Oscillation
A lever arm that repeatedly oscillates back and forth during idle or more speeds means the the inside damper mechanism in the tensioner pulley has weakened or broken. This triggers sporadic tension pressure on the belt and can manifest itself with intermittent chirping noises.