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The serpentine belt on the Land Rover Tdi is know
for it's screeching, usually only until hot but not always.
Firstly you need to check that you have the
correct belt - There are two different belts used on the 300Tdi Up to engine No 16L25165 use belt No ERR3287 After this use ERR 5911
Secondly make sure that the tensioner pulley
bearing on the belt is OK.
Some people have found that the belt and
pulleys get clogged with dirt and small stones.
The solution is to remove the belt and
carefully clean each groove with soap and a tooth brush so similar tool,
the grooves in the various pulleys must also be carefully cleaned out.
Thirdly have a look at the following article:
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.
The-Bonnet
Harmonics
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).
Figure 1
Radial sliding motion of V-ribbed belt.
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.
Diagnosing The Problem
In ongoing studies at the Gates Belt Testing Laboratory in Denver,
engineers have gained the following insights to noise resulting from
misalignment:
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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.
-
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.
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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).
-
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.
-
Flat or crowned pulleys have no grooves to guide the belt and
can be a common source of drive misalignment.
-
Smaller diameter pulleys exhibit less sensitivity to
misalignment noise due to their smaller area of sliding contact
between the belt and pulley.
-
Misalignment noise is generally loudest at idle speed and
diminishes with increasing engine rpm, often vanishing
altogether above 2500 rpm.
-
The presence of high humidity (or a damp belt) often increases
the likelihood for misalignment noise to occur.
he Work Shop
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.
Corrective Action
Failure to correct conditions responsible for belt noise will result
in the problem returning, usually within 5 000 Km 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.
With tanks to Detlev Friemelt detlev@iafrica.com
for sending this to us
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