A belt tension pulley is used to maintain adequate pressure on a drive belt to ensure no slipping of the belt occurs while it is in an operational mode. Depending on the size, type and style of rubber belt used on any given machine, the belt tension pulley can be adjusted to give the proper amount of support without applying an extraordinary amount of pressure on the belt. This also saves wear on the bearings of all the pulleys being driven by the belt. On a vehicle engine, this type of pulley is commonly found on a spring-loaded bracket that is also used in belt removal from the system.
Early automobiles used adjustable engine accessories to tighten the fan belt, and a belt tension pulley was not required in the belt system. Modern vehicles use a single, flat serpentine-style fan belt with no adjustable engine components. This mandates the use of a belt tension pulley in order to keep the belt tight as well as to react to belt stretch and aging. By placing the pulley on a spring-loaded bracket, the belt can continually be adjusted, as it might become stretched and loose. The spring will ensure the maximum amount of pressure is placed on the belt at all times.
Regardless of the style of tensioner bracket the pulley is affixed to, the typical arrangement for the pulley is to be mounted to the bracket with a single bolt through the center of the pulley and into the bracket. The pulley is equipped with a bearing to provide long life as it spins with the belt. A damaged bearing requires the entire assembly be replaced in the form of a new pulley. The new belt tension pulley is simply bolted into place and the belt placed around it in the specified manner.
Often, a squeaking belt is not the result of a bad bearing or pulley, but rather the result of an old and hardened belt. As the rubber ages, it can become hard and brittle through the loss of critical oils from the rubber material. Applying a small amount of belt dressing as the belt turns will occasionally restore the oils to the rubber and will eliminate the noises coming from the belt. Occasionally, the belt tension pulley will have a bearing or a spring go bad and require service. Installing the new parts will commonly cure all noise from the belt system.