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

How do you modify a tensioner pulley?
Convert the adjustment bolt privately, top or bottom level of the pulley counterclockwise with the ratchet and socket until the accessory belt is loose enough to remove. Tighten the tensioner pulley by turning the adjustment bolt clockwise with the ratchet and socket before belt is tight.
How do I know

A tensioner pulley guides the belt around the tensioner and allows the belt to spin as the tensioner maintains pressure against it. A failing tensioner pulley could cause power reduction and harm to your belt-driven devices. You may have a failing tensioner pulley in the event that you hear any squeaking or squealing beneath the hood. Bearings on the pulley can wear out, causing noise and temperature. Pulleys are usually manufactured from either plastic or metallic, so examine the pulley itself for just about any damage as well. At O’Reilly Automobile Parts, we’ve tensioner pulleys available for many vehicle models.

The automatic pulley tensioner comes with an internal spring-loaded mechanism that keeps the serpentine belt under constant tension. Its design allows it to keep carefully the serpentine belt taut, so that the other item pulleys rotate at the same rpm (revolutions per minute) while under the same secure pressure. Tensioner pulleys can also absorb slight shock loads that happen when the air conditioner cuts on / off. As a frequently rotating element, the pulley tensioner can provide off some warning signs before failure.

Rust and Corrosion
The pulley tensioner sits exposed to the elements at the front end of the engine. Subjected to puddled water “splash-up,” with time the tensioner arm and pulley device can rust. Rust can freeze the computerized tensioner device or corrode the shaft bearings, that may cause a frozen location in the adjustment pressure. Without the proper tension, the belt can slide.
Debris Contamination
Rocks, gravel and other road debris can be thrown up into the tensioner pulley grooves and jam the mechanism. This can permit the serpentine belt to slide on the tensioner pulley and shed. Overheated pulley heat range results, and eventually the serpentine belt will melt and snap off.
Pulley Tensioner Spring
The pulley tensioner spring within the housing may become weak from age and repeated contact with heat. This causes the belt to flutter and skip rather than maintaining a constant strain on the pulley. Symptoms of a fragile spring present as glazing on the lower of the serpentine belt, with an intermittent flickering of the dashboard’s charging light indicator. Squealing or squeaking will end up being observed at the belt location.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, this means the inside shaft bearings have worn. This will cause a pulley misalignment. Terrible bearings trigger an audible growling noise. The outer ends of the serpentine belt will fray and stretch out the belt. Eventually the rubber belt grooves flatten out and cause major slippage. An excessively wobbling pulley can throw the belt off, leading to all the extras to quit functioning.
Lever Arm Freeplay
Some tensioner pulleys have markings on the casing that indicate the maximum selection that the pulley can travel. If the lever arm of the tensioner rides under or over the designated mark, this implies a stretched belt or a lever arm which has jammed in a single position.
Pulley Misaligment
The tensioner pulley face must match up to the other accessory pulleys with a parallel alignment. Placing an extended, straightedge ruler against the face of the tensioner pulley, and then flushing it against another accessory pulley, can gauge the angle. Any off-angle measurement indicates put on shaft bearings in the pulley casing.
Serpentine Belt Noise
A moderately worn serpentine belt gives off a constant squeaking noise during engine idle. Belts which have worn severely job a loud chirping or squealing appear. The cause details to a glazed, put on or cracked belt. Dry or partially frozen tensioner pulley bearings can cause such sounds by deteriorating the belt prematurely.
Lever Arm Oscillation
A lever arm that repeatedly oscillates back and forth during idle or higher speeds means the the within damper mechanism in the tensioner pulley has weakened or broken. This triggers sporadic tension strain on the belt and will manifest itself with intermittent chirping sounds.