From: Arthur J Baumgartner The article below from one of the larger belt manufacturers in the US,
(Gates Rubber Co.) gives a good explanation for the V-ribbed belt noise
experienced by many 3rd gen owners and suggests one remedy that I have
found works, (removing the noisy belt and reinstalling it so that it
rotates in the opposite direction, in other words fipping it over and then
reinstalling it).
The article together with accompanying figures, (not included below) can
be viewed at the Beltnoise
page of the Gates Rubber Co. website.
Terms such as chirp, squeal, rumble and yelp have been used in the
automotive industry to describe noises caused by friction-induced vibration
in engine accessory drive belts. The following report, based on testing by
The Gates Rubber Company, examines primary causes and remedies for this
problem.
To the educated ear, drive belt noise can be as distinctive as the notes
on a musical scale
All sounds that are audible to the human ear have their origins in some
vibrating surface. For example, intermittent chirping that increases in
frequency as the engine is revved up can be the result of belt vibration
caused by misaligned drive pulleys -- a leading cause of belt noise. As a
misaligned V-ribbed belt span enters the grooves of a pulley, initial
contact is made with only one side of the V-groove. The greater the
misalignment angle, the greater the radial sliding length experienced
by the belt ribs as the belt seats in the pulley causing frictional
vibrations, or chirping (see Figure 1).
Low belt tension, contamination and belt vibration are other common
sources of belt noise. A screeching or squealing noise that occurs when
pulling away from a stop normally indicates a lack of tension; check belt
tension and automatic tensioners.
A tapping or grinding noise caused by a pebble imbedded in the belt is a
common occurrence. Grinding sound also can result from damaged bearings,
which must be replaced, aligned and lubricated to eliminate the noise and
further damage.
Vibration and noise can develop over time as drive components such as
pulleys and spring tensioners wear out of tolerance, as bearings and
brackets loosen, or as belts wear and stretch.
In ongoing studies at the Gates Belt Testing Laboratory in Denver,
engineers have gained the following insights to noise resulting from
misalignment:
1. Chirp noise caused by drive misalignment occurs upon entry of the
span into the pulley as belt ribs seat into the pulley grooves, not as the
belt exits.
2. Belts are less likely to generate misalignment noise when they are in
new condition. As belts wear in, they develop a smooth, glossy surface
which increases the likelihood for noise. This wear-in process is
accelerated when misalignment conditions exist in the drive.
3. The angle between belt span and pulley is the critical factor
responsible for causing the "chirp" associated with misalignment noise.
Misalignment angle can result from many different combinations of pulley
positions -- parallel and angular are two typical examples (see Figures 2 &
3).
4. Misalignment noise occurs most frequently on the shortest spans in a
drive, most often between a backside pulley and an adjacent accessory
pulley. Proper pulley alignment is particularly critical in these
locations.
5. Flat or crowned pulleys have no grooves to guide the belt and can be
a common source of drive misalignment.
6. Smaller diameter pulleys exhibit less sensitivity to misalignment
noise due to their smaller area of sliding contact between the belt and
pulley.
7. Misalignment noise is generally loudest at idle speed and diminishes
with increasing engine rpm, often vanishing altogether above 2500 rpm.
8. The presence of high humidity (or a damp belt) often increases the
likelihood for misalignment noise to occur.
Whenever a vehicle owner complains of belt noise, Gates says it is
important to determine the type of noise and under what circumstances it
occurs. A solution to a noise problem caused by drive misalignment is not
likely to resolve a slip noise problem that may be caused by insufficient
tension or some other problem. Find out if the problem is more noticeable
in the morning while the engine is cool (cool, damp belt). Is the noise
loudest at idle speed, or when accelerating or shifting gears (rapid
changes in engine speed can cause a belt to slip)?
Next, attempt to recreate the problem in the service bay. Using a spray
bottle filled with water, mist the belt lightly. If the noise level recedes
for several seconds, then returns louder, a misalignment problem is likely.
If the noise immediately increases after the belt is sprayed, slipping is
likely.
If the water spray test is inconclusive, or not successful at diagnosing
the problem, attempt to remove the noisy belt and re-install it so that the
belt runs in the opposite direction. Because misalignment noise is
influenced by the direction of misalignment in the drive, flipping the belt
around in this manner will eliminate or significantly diminish (temporarily)
any noise caused by drive misalignment. If the noise remains unchanged, the
problem is not likely related to drive alignment.
In actual applications, the highest occurrence of belt noise due to
misalignment comes from short belt spans entering large diameter pulleys.
Service technicians are encouraged to look for the source of noise wherever
these conditions exist.
Also, look for replaced drive components, such as a rebuilt alternator,
which may have been improperly installed resulting in pulley misalignment.
Failure to correct conditions responsible for belt noise will result in
the problem returning, usually within 3,000 miles or less.
If the problem is drive-related, depending on the degree of misalignment,
it may be possible to modify the noise level by installing a new belt with
noise-resistant properties.
Gates engineers have developed new elastomeric compounds that are
noise-resistant under various environmental and wear conditions. These new
belts feature additives that enable them to slide easily into and out of the
pulley. This low-noise construction helps to eliminate belt noise from most
misalignment situations.
In the case of severe misalignment, repositioning of drive components
using shims, or by changing the press fit of the pulley or the shaft, may
be required. Pulley alignment and tension must be correct on all V-ribbed
belt applications for the drive to operate properly.
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Date: Thu, 12 Dec 1996 16:35:13 -0800
Troubleshooting V-ribbed Belt Noise - (from Gates Rubber Co.)
Under-The-Hood Harmonics
Radial sliding motion of V-ribbed belt.
Diagnosing The Problem
Figure 2 Parallel misalignment.
Figure 3 Angular misalignment.
In The Shop
Corrective Action
