'91 Burb, bearing noise in serpentine system

[Daveo91Burb]

Since I bought my '91 (350 TBI) in July it has had a bearing-type of noise or chirp in one of the accessories in the serpentine system. It's worse when cold. So far I have replaced the water pump (it was leaking out the weep hole so it needed it anyway), the tensioner pulley, and the idler pulley. Still has the noise. I've also taken the fan off and run it for a few minutes - still has the noise so I know it's not the fan clutch. Don't think it's the A/C comp since the noise is independent of whether or not that clutch is engaged. I've also run the engine for a minute or two without the belt just to verify noise goes away - it does. Pretty much leaves power steering pump and alternator? Both spin noiseless-ly by hand and alternator looks pretty new. Thoughts on what this could be or how to diagnose further? Doesn't seem to be a big problem, but it's embarrassing!

 

[bucket]

Have you tried the trick of touching different parts with a long screwdriver and putting the handle to your ear?

I'd say the alt is far more likely than the PS pump.

 

[89Suburban]

It's the belt.

 

[chengny]

If you have checked each rotating assembly and cannot seem to identify the source of the noise - it's time to look at the belt itself as the cause (specifically a misalignment/tension issue). Read this stuff from a Dayco handout:

DIAGNOSING MISALIGNMENT AND BELT NOISE


One of the biggest burdens today for professional technicians and do-it-yourselfers is belt noise, and the No. 1 cause for belt noise is misalignment.

There are two distinctively different types of belt noise, “Chirp” and “Squeal”.

Each has its own unique characteristics, causes and solutions. One method to determine if the noise is a chirp or squeal is to use a water squirt bottle and spray the rib side of the belt while the vehicle is running. If the noise gets louder, it’s a squeal. If the noise goes away, it’s a chirp.

“Chirp” is a sharp, high-pitched, repetitive noise of short duration, usually worse at low engine speeds (idle). As belt speed increases, the belt noise may blend into one audible noise, but most likely diminish in intensity such that it won’t be detected.

Most chirp noises occur as a short belt span enters into a grooved pulley, typically after exiting a backside pulley.

Causes:

Pulley misalignment
Improper installation
Belt ribs extremely worn
Worn pulley bearings (causing pulley wobble/excessive free-rock)
Contamination (oil, power steering fluid, antifreeze, belt dressing, brake cleaner, etc.

Solutions to misalignment:

Check the alignment of all pulleys, either with a straight edge or laser alignment device, such as laser tool found in the Dayco Belt Diagnostic Kit
Insure all accessory pulleys and brackets are tightened snug to mounting surfaces
Inspect and replace all accessories / pulleys that are difficult to rotate (i.e. rough/seized bearings), or show excessive wobble / free rock
Power steering pulleys are a very common cause of misalignment
Warning: Any existing misalignment condition probably caused pre-mature wear of the belt ribs on the old belt. A new belt is recommended once the accessory drive has been realigned.

“Squeal” is a high pitched noise, typically lasting several seconds in duration. This type of noise will typically increase in volume as the engine speed increases, and is caused by relative slip between the belt and pulleys.

Causes:

Low belt tension

Low installation tension (manually tensioned drives), belt stretch, extreme belt wear, tensioner spring degradation or a belt that is too long

High accessory / idler drag

Seized bearings or accessory failure / lock –up

Environmental contamination

Fluid contamination on the belt (oil, power steering fluid, antifreeze, belt dressing, brake cleaner, etc.)

A hard splash of water such that causes the belt to hydroplane or loose traction


Solutions to tensioning problems:

Belts installed on vehicles with manual tension drives should be properly tensioned during installation, and re-tensioned after 5 minutes of run-in (30 lbs. per rib). A belt installed incorrectly will make noise and if not remedied quickly, will need to be replaced


On systems equipped with an automatic tensioner, the tensioner pulley should turn freely without binding, the tensioner arm should move smoothly through its entire range of motion and there should be adequate tension. Replace the tensioner and /or pulley as required

 

[Daveo91Burb]

Thanks guys. I'll try the water spray trick and look for misaligned pulleys. Although the guy I bought this from seemed to know what he was doing, I've found that he took the quick way out on projects at least sometimes!

 

[chengny]

As reference - some good info on types of belt/pulley misalignment and how to measure/eliminate it:


Nature of Misalignment

As with shaft misalignment, there are various types of belt misalignment. In practice, a combination of different misalignment is often encountered simultaneously. For this reason, it is important that an alignment instrument both diagnoses and details the nature of the machine''s misalignment. The following illustrations depict the three different types of belt misalignment:

You must be registered for see images attach

Vertical angle or twisted misalignment:

Occurs when one of the pulleys has an angular error from the vertical angle plane. This is usually caused by incorrect positioning of the machine and can be corrected by lifting either the front or rear feet of the motor to which the pulley is attached, depending on the direction of the vertical angle error. This differs from shaft alignment in that one never moves both feet in a vertical direction to reach the desired result.

Horizontal angle misalignment:

Occurs when the driver and the driven unit are not positioned parallel to each other. Incorrect positioning of applications, such as the motor, typically can cause this type of misalignment. Horizontal angle misalignment generally can be corrected by moving the front or rear feet forward or backward on their guides, depending on the direction of the horizontal angle error, in order to twist the motor around its center.

Parallel misalignment:

This is the least complex form of misalignment. It is often caused by the incorrect positioning of the motor along its shaft axis, positioned either too far forward or backward compared to the other shaft. Or it can be caused by incorrect positioning of the pulleys on their respective shaft, where one of the pulleys needs to be adjusted on the shaft.

Belt Alignment Methods


Belt alignment can be performed by either traditional visual methods or the laser method. Traditional methods usually employ strings and/or straightedges.

You must be registered for see images attach

The main advantage of these traditional methods is the limited length of time needed for adjustment, although the use of a straightedge takes more time than visual assessment alone. The major disadvantage is the lack of accuracy. For example, some belt manufacturers recommend a maximum misalignment of 0.5 degrees or even 0.25 degrees, which is difficult to accomplish by using visual assessment. These traditional low-tech methods involve a good deal of trial and error, naked eye approximation, and rough estimates. All told, that means a large margin for error, which is unacceptable for precision pulley alignment.

 

[350runner]

89suburban and Jerry are right on! Such detail...

Sent from the dust in front of you!

 

[bucket]

V-belt misalignment is a myth. Anyone ever looked in the back of a Corvair?

 

[HotRodPC]

IIRC a Corvair has a belt that runs an air cooler fan that is actually twisted since the 2 pullies are actually 90 degrees of each other. One pully is vertical, one is horizontal. Been a long long time since I seen a corvair motor, but that's what I am thinking for some reason.

 

[HotRodPC]

BTW, this tool is a great help in matters like these. I've bought these on sale before for as low as $1.99. I bought it cuz it was cheap and was extremely impressed when I had a reason to use it.
http://www.harborfreight.com/mechanics-stethoscope-69913.html

 

[bucket]

IIRC a Corvair has a belt that runs an air cooler fan that is actually twisted since the 2 pullies are actually 90 degrees of each other. One pully is vertical, one is horizontal. Been a long long time since I seen a corvair motor, but that's what I am thinking for some reason.

Yep, it goes around several bends once it's all said and done. Claas balers have a similar belt routing style, but it's even crazier.

 

[Stewzer55]

Power steering pumps squeak when the reservoir is low, check the fluid level.

 

[Chaz]

I've had 2 alternators go out in past 2 years. Well they really didn't go out just started squeaking. I don't know how your pulleys could be out of alignment because if there bolted on right they should be in alignment. I would think if theyre out of alignment somehow it would be obvious by looking at it.

 

[HotRodPC]

I've had 2 alternators go out in past 2 years. Well they really didn't go out just started squeaking. I don't know how your pulleys could be out of alignment because if there bolted on right they should be in alignment. I would think if theyre out of alignment somehow it would be obvious by looking at it.

2 alternators in 2 years tells me they are discount auto part store Lifetime Warranty alternators, and that is 100% normal and par for the course. Not sure why that it is, but it just is with GM alternators from Auto Zone, O'reilys and Advanced Auto.

 

[Daveo91Burb]

Problem solved! I think. Dirty belt and/or pulleys. I took the belt off and cleaned it and all pulleys with carb cleaner. Still squeaked when I started it, but drove it for 5 miles or so and seems to be gone. Would make sense since old water pump was leaking through weep hole and coolant may have gotten on belt. Also some spray lube may have found its way there. If I still have problems I will replace belt even though this one is visibly OK. Thanks for all the advice and discussion - definitely some good stuff here but I think mine was just a simple solution.