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

How do you modify a tensioner pulley?
Turn the adjustment bolt on the side, top or bottom of the pulley counterclockwise with the ratchet and socket until the item 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 you know

A tensioner pulley courses the belt around the tensioner and allows the belt to spin while the tensioner maintains pressure against it. A failing tensioner pulley can cause power loss 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 degrade, causing noise and temperature. Pulleys are usually manufactured from either plastic or metal, so examine the pulley itself for any damage aswell. At O’Reilly Vehicle Parts, we’ve tensioner pulleys designed for many vehicle models.

The automatic pulley tensioner has an internal spring-loaded mechanism that keeps the serpentine belt under continuous tension. Its design permits it to keep carefully the serpentine belt taut, in order that the other accessory pulleys rotate at the same rpm (revolutions each and every minute) while beneath the same secure pressure. Tensioner pulleys can also absorb slight shock loads that happen when the air conditioner cuts on / off. As a continuously rotating aspect, the pulley tensioner can give 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,” as time passes the tensioner arm and pulley system can rust. Rust can freeze the programmed tensioner device or rot the shaft bearings, that will cause a frozen position in the adjustment pressure. Without the correct pressure, 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 burn up. Overheated pulley temperature 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 exposure to heat. This causes the belt to flutter and skip rather than maintaining a constant pressure on the pulley. Symptoms of a poor spring demonstrate as glazing on the underside of the serpentine belt, with an intermittent flickering of the dashboard’s charging light indicator. Squealing or squeaking will be heard at the belt location.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, this means the inside shaft bearings have worn. This may cause a pulley misalignment. Negative bearings trigger an audible growling noises. The outer ends of the serpentine belt will fray and stretch the belt. Eventually the rubberized belt grooves flatten out and cause key slippage. An excessively wobbling pulley can toss the belt off, leading to all the extras 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 over 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 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 item pulley, can gauge the angle. Any off-position measurement indicates worn shaft bearings in the pulley casing.
Serpentine Belt Noise
A moderately donned serpentine belt gives off a constant squeaking noises during engine idle. Belts that have worn severely project a loud chirping or squealing audio. The cause points to a glazed, put on or cracked belt. Dry or partially frozen tensioner pulley bearings can cause such noises by wearing out the belt prematurely.
Lever Arm Oscillation
A lever arm that repeatedly oscillates backwards and forwards during idle or more speeds means the the inside damper mechanism in the tensioner pulley has weakened or broken. This causes sporadic tension pressure on the belt and can manifest itself with intermittent chirping noises.