squeal from alternator, water pump or belt?

[Sublime]

My truck developed a squeal when the engine was cool at 1st start up. It would go away almost immediately. I assumed it was a bad belt - so over the winter I changed both belts, alternator/water pump and power steering. I did not start the truck till recently and now the squeal is worse. happens when I first start it, then quiets till I rev the motor. It seams to be worse the cooler the weather. Today I removed the alternator/water pump belt and the squeal is gone. The water pump bearing is tight and spins freely, the alternator is charging, pulley is tight and spins freely. That leads me back to a "bad" new belt? What are the chances ?? Could it be a bad alternator or water pump somehow? Ideas?
After taking pictures of the belt I got to wondering if the belt is the right width, it almost looks to skinny. and of course I threw the old belt away

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[Snoots]

I went thru a similar problem and tried your fixes. Turned out to be a bad bearing in the alternator.
If that happens to be your case I'd change out the SI 10 to a CS130.

 

[DavesJimmy]

My 79 c10 does the same thing in the morning when its cool.. i haven't tried to fix it yet. But since it doesnt do it when its warm out im guessing that maybe the belts are installed to tight. So when its cold they shrink and are to tight and when it warms up out they streatch out a bit. Not 100% sure but worth a try i know you dont want them to loose or they'll spin on the pulleys. I think 1/2" of movement when under tension..

 

[1987 GMC Jimmy]

No grinding when you spin the alternator by hand? Are all the accessories bolted in properly? I’d take off the alternator belt when it’s cold and see what happens when you start it up. That’s gonna be the best way to isolate this. I know it’s a pain, but it looks like you don’t have the air pump so it should be the first belt, right?

 

[chengny]

No, you're okay on that. The belt seems to be riding at just about the correct depth in the sheave groove. The reason it appears to be too deep is due to the design of the sheaves used in automotive applications. The sheaves used on stationary machinery have a much sharper profile - almost like they have been turned in a lathe. The sheaves used for automotive applications (on alternators for example) have a softer contour along with an upper edge that rises above - tapers away from - the groove. This design is much more forgiving to belt misalignment. The dwg below is from the Gates handbook and it shows the proper depth of the belt in the groove. I added those extensions to the left hand dwg to demonstrate the difference between an automotive and industrial sheave:

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But speaking of misalignment; It could be an optical illusion (or just the camera angle), but it appears that driven pulley on your alternator has some pretty serious (vertical) angular misalignment issues. If it is what it appears to be, that could cause belt squeal on initial application of load. First, note the difference in the gaps at the top and bottom (yellow is wide and red is thin):

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Next, see how the line of the belt from the water pump to the alternator is not in the same plane as the line of the belt from the alternator to the crank pulley:

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You might want to check alignment using a straight edge as shown below:

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[Sublime]

That is great information and the belt observation I totally missed. chengny you went above and beyond .... Thank you.
I have a different brand belt on its way from rock auto - I just need to make sure the alignment is correct.

 

[Hatchet54]

Hey OP, did you ever nail down the culprit on this? My truck is doing the exact same thing.

 

[Matt69olds]

You may try roughing up the pulley sheave. Carefully (and I emphasize CAREFULLY!!) use a stiff wire brush on the pulley while the engine is running. You can also rough up the belt

 

[73cheyenne]

Mine has done the same thing since new. The belt doesn't wrap around the alternator pulley very far. When you first start it the alternator is in full charge mode and takes more torque than the belt can provide. I don't know if there is a fix. I just don't worry about it.

 

[eskimomann209]

I love using the dove soap on the belt to see if it stops the squeaking.
This’ll tell ya if it’s the belt.
But that doesn’t mean it’s not alignment. It can still stop the squeak and still have an alignment issue but it’ll rule out bearings