What does the strain pulley do?
A drive belt tensioner is a pulley mounted on a spring device 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 drive the various engine accessories.

How do you modify a tensioner pulley?
Transform 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 before belt is tight.
How do I know

A tensioner pulley manuals 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 reduction and harm to your belt-driven devices. You may 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 heat. Pulleys are usually manufactured from either plastic or steel, so check the pulley itself for any damage aswell. At O’Reilly Automotive 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 continuous tension. Its design permits it to keep carefully the serpentine belt taut, to ensure that the other accessory pulleys rotate at the same rpm (revolutions each and every minute) while under the same safe pressure. Tensioner pulleys may also absorb mild shock loads that happen when the air conditioning unit cuts on and off. As a constantly 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 end of the engine. Subjected to puddled water “splash-up,” as time passes the tensioner arm and pulley mechanism can rust. Corrosion can freeze the automatic tensioner device or corrode the shaft bearings, which will cause a frozen position in the adjustment pressure. Without the correct tension, the belt can slip.
Debris Contamination
Rocks, gravel and other highway debris can be thrown up in to the tensioner pulley grooves and jam the device. This can permit the serpentine belt to slide on the tensioner pulley and burn. Overheated pulley temperature results, and finally 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 exposure to heat. This triggers the belt to flutter and skip instead of maintaining a constant strain on the pulley. Symptoms of a poor spring demonstrate as glazing on the lower of the serpentine belt, with an occasional flickering of the dashboard’s charging lumination indicator. Squealing or squeaking will become observed at the belt area.
Pulley Wobble
If the tensioner pulley wobbles on its shaft, it means the interior shaft bearings have worn. This will cause a pulley misalignment. Bad bearings cause an audible growling noises. The outer ends of the serpentine belt will fray and stretch out the belt. Ultimately the rubber belt grooves flatten out and cause main slippage. An excessively wobbling pulley can toss the belt off, leading to all the extras to quit functioning.
Lever Arm Freeplay
Some tensioner pulleys possess markings on the housing that indicate the maximum selection 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 a single 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 item pulley, can measure the angle. Any off-angle measurement indicates put on 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 may have worn severely task a loud chirping or squealing audio. The cause factors to a glazed, put on or cracked belt. Dried out 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 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 sounds.