GATES TRAINING: Diagnosing Belt Noise – The Spray Bottle Test

Last Updated: 14 Jun 2019
GATES TRAINING: Diagnosing Belt Noise - The Spray Bottle Test

The root cause and location of V-Rib belt noise is often a difficult diagnosis. Belt noise most often is not a problem with the belt, so just replacing the belt will only delay finding the real problem. Belt chirp is generally a misalignment problem between the component pulleys and idlers in the belt drive system. Belt squeal, on the other hand, indicates a loss of tension either from a worn belt, failing tensioner, or both. Both must be replaced to bring the system back to a like-new condition. Here’s a simple test that will help you determine whether belt noise is a system misalignment or a belt tension problem.

How to Diagnose an Alignment Problem

If it’s an alignment problem this test can help locate the component or pulley that is out of alignment. Before we start though, here’s a word of caution. This test is performed with the engine running, so it’s highly recommended that a professional technician conduct this test. All clothing, body parts, and tools must be kept clear of moving engine parts. Failure to do so can result in severe injury or even death. First, fill a spray bottle with tap water.

Make sure it’s only water since you’ll be spraying it on the belt. Next, duplicate the conditions when belt noise is normally heard. For example, if you hear belt chirp when the engine is cold perform this test in the morning. The objective is to spray water on the V-Rib side of the belt where the belt enters the pulley, in the location where the noise seems to come from. The right location can be difficult to determine, but frequently misalignment noise originates from the shortest belt spam. In other words the belt section with the shortest distance between two pulleys.

This is especially true if one of the short span pulleys operates on the back side of the belt. A water pump, for example, is powered by the backside of the V-Rib belt. Look to see if there is a short span between this pulley and the next. Start the engine and spray the V-Rib side of the belt where it enters the pulley. The water will act as a lubricant.

  • If belt noise becomes more pronounced, that is if the squealing gets louder when the belt is sprayed, it means there is not enough tension on the belt. The belt and the tensioner should both be replaced.
  • If on the other hand the noise or chirping goes away momentarily when the belt is sprayed and then it returns, it means one or more of the pulleys at that location are out of alignment.
  • If there is no change in belt noise look for the next shortest belt span and spray again where the belt enters the second pulley in the span. If the noise goes away and then returns you have identified the location of the misalignment. The belt can be removed and the alignment checked with a laser alignment tool available from Gates.
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