Accessory Belt Idler Pulley
You hear some unusual screeching noise as soon as you start your engine. But if upon checking your engine, you don't see anything wrong, then don't panic because it's just probably your belt idler pulley. Bolted onto the engine block, this timing belt pulley may look almost exactly like the belt tensioner pulley-it looks like a bearing with a very thick wall.
Like the belt tensioner pulley, it's designed to remove that annoying belt vibration that's caused by excessive belt slack. The only difference between them is that the tensioner is mounted on an adjustable bolt, while the idler pulley isn't. Aside from increasing belt tension, the belt idler pulley also prevents the flat belt drive from slipping, which is surely the last thing that you want to happen to your vehicle. Though its outer wall is smooth, it has retainers on the edges or a groove along the middle to keep the belt in place.
The best kind of pulley is that constructed from special glass-filled polymers and has smoother surface and stiffer dimensions for lesser vibration of your ride's belt. Also, its seals should be of double high-temperature standards for better bearing performance. To preserve it, make sure that its ball bearings are lubricated well. And to avoid frequent replacement, you can get it from a reliable auto parts store like The Family Car.