What does the strain pulley do?
A drive belt tensioner is a pulley mounted on a spring system or adjustable pivot point that is utilized 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 adjust a tensioner pulley?
Switch the adjustment bolt on the side, top or bottom level of the pulley counterclockwise with the ratchet and socket before equipment belt is loose enough to eliminate. Tighten the tensioner pulley by turning the adjustment bolt clockwise with the ratchet and socket until the belt is tight.
How do I know

A tensioner pulley tutorials 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 reduction and harm to your belt-driven devices. You could have a failing tensioner pulley if you hear any squeaking or squealing beneath the hood. Bearings on the pulley can wear out, causing noise and temperature. Pulleys are usually made of either plastic or metal, so verify the pulley itself for just about any damage as well. At O’Reilly Vehicle 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 frequent tension. Its design enables it to keep the serpentine belt taut, so that the other accessory pulleys rotate at the same rpm (revolutions per minute) while beneath the same safe pressure. Tensioner pulleys may also absorb moderate shock loads that happen when the air conditioner cuts on and off. As a regularly rotating aspect, the pulley tensioner can provide off some warning signs before failure.

Rust and Corrosion
The pulley tensioner sits subjected to the elements at the front of the engine. Put through puddled water “splash-up,” with time the tensioner arm and pulley mechanism can rust. Rust can freeze the automated tensioner device or rot the shaft bearings, which will cause a frozen placement in the adjustment pressure. Without the proper pressure, the belt can slide.
Debris Contamination
Rocks, gravel and other highway debris can be thrown up into the tensioner pulley grooves and jam the mechanism. This can allow the serpentine belt to slide on the tensioner pulley and lose. Overheated pulley temp results, and eventually the serpentine belt will melt and snap off.
Pulley Tensioner Spring
The pulley tensioner spring inside 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 weak spring display as glazing on the lower of the serpentine belt, with an intermittent flickering of the dashboard’s charging light indicator. Squealing or squeaking will always be heard at the belt site.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, it means the inside shaft bearings have worn. This will cause a pulley misalignment. Negative bearings cause an audible growling noises. The outer ends of the serpentine belt will fray and stretch the belt. Finally the rubber belt grooves flatten out and cause major slippage. An excessively wobbling pulley can throw the belt off, triggering all the gadgets to quit functioning.
Lever Arm Freeplay
Some tensioner pulleys have markings on the housing that indicate the utmost range that the pulley can travel. If the lever arm of the tensioner rides under or higher the designated mark, it indicates 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 of the tensioner pulley, and flushing it against another accessory pulley, can gauge the angle. Any off-position measurement indicates worn shaft bearings in the pulley casing.
Serpentine Belt Noise
A moderately put on serpentine belt produces a constant squeaking noises during engine idle. Belts that have worn severely project a loud chirping or squealing audio. The cause items to a glazed, donned or cracked belt. Dry or partially frozen tensioner pulley bearings could cause such noises 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 noises.