Serpentine belt comes off when wet

[DrCharles]

My '93's serpentine belt is driving me nuts... it pops off whenever water splashes onto the engine from underneath (and our dirt roads + rain offer plenty of opportunities). Since we had a cow/flat rock rain last night, it threw the belt twice today!

The first and only other time this happened (a few months ago) it was extremely humid and the temp had suddenly dropped, so condensation and fog on every metal surface. Started the truck and the belt instantly jumped off. Put it back on and no problems until today.

I have recently replaced the tensioner (O'Reilly) and installed a 111.5" belt to stop the chirping. That one was tight enough when new to require partially dismounting the alternator. It's stretched enough now with a couple thousand miles use that it can be slipped over the alternator pulley with the tensioner fully compressed. Also the chirping has started again!! Nothing looks loose or rattly.

1) Is there supposed to be a splash shield beneath the radiator? Keeping the water away from the belt in the first place would be a start.

2) The belt seems to ride rather close to the rounded front edge of the tensioner pulley, and I'll bet that's where it pops off first. I'm assuming that a sudden slip/grab when wet is what's causing it to jump off in the first place. Is there a tensioner with a lip on the pulley(s) that would help keep the belt in place?

 

[Thewespaul]

Yes there is a splash shield from the factory, but I rarely see one anymore. I sell an oversized pulley for the tensioner and idler, ive had good luck with them fixing belt issues. These are the pulleys that came on the ambulance packages that had the large shock to accommodate the monster alternators those ran.


Larger pulley on the right

You must be registered for see images attach

 

[DrCharles]

Is that larger pulley also wider than the original? That should help keep the belt from jumping.

How much more belt length is needed?

It's just strange that it'll run indefinitely, until I go through a big puddle and water hits the belt...

 

[Thewespaul]

Only slightly wider, there’s only so much clearance between the tensioner and pulley

 

[Dirtleg]

Does your truck still have the, umm I don't know the proper name, alignment tab on I think the vacuum pump near the pulley? It's my opinion that it keeps the belt from jumping if the tensioner bounces for any reason.

Also are you sure you don't have an out of round crank or waterpump pulley? Or really any pulley.

 

[DrCharles]

Thanks. I've been reading through all the threads on Oilburners about belt jumping and saw that one just a few minutes ago... will go out and look in the morning, and if it's not there I will add one

Nothing's wobbling that I can see (an out of round pulley would cause a repeating tensioner bounce, right?)

Is this the right splash panel? https://www.rockauto.com/en/catalog/ford,1993,f-250,7.3l+v8+diesel,1124660,body,valance+panel,820

 

[DrCharles]

Only slightly wider, there’s only so much clearance between the tensioner and pulley

On mine it looks like the round-nosed tensioner pulley needs more width towards the front of the truck. Is it possible to shim the pulley?

 

[Thewespaul]

Yep, you can use a properly sized washer that matches the bearing id and od

 

[Ironman03R]

I had this same problem on a Dodge caravan years ago. I never fixed it just carried a 15mm wrench wirh me. When **** hit the fan I gave the van to my ex but kept the wrench...lol

 

[Oledirtypearl86]

Had this problem with my suburban old timer told me to use some emerycloth on the pulleys for the flatside and it worked like a charm no more issues with the belt

 

[chillman88]

Had this problem with my suburban old timer told me to use some emerycloth on the pulleys for the flatside and it worked like a charm no more issues with the belt

This is the kind of stuff the kids in the shop don't know about. All these neat little old-timer tricks. Thanks, that's a trick I'll remember.

 

[Oledirtypearl86]

I'm

This is the kind of stuff the kids in the shop don't know about. All these neat little old-timer tricks. Thanks, that's a trick I'll remember.

Yeah All I did was just enough to scuff the idler and tensioner a little I did it with it running and used like a 220 grit Emery paper but watch your fingers please running motors can bite

 

[DrCharles]

I'll try scuffing the pulleys. Also maybe a shim to move them a bit more forward (this pic is where the belt normally rides).

For a previous poster, the little bracket on the vac pump is in place. I'm pretty sure it's jumping off the tensioner/idler.

You must be registered for see images attach

 

[DrCharles]

OK, the three smooth pulleys are scuffed and a large (9/16" ID) copper crush washer used as a shim after a few strokes with a rat-tail file. I also noted that the front rounded edge of the tensioner pulley is very slightly larger in diameter than the flat surface. Although it's counter-intuitive, to keep a flat belt centered on a pulley you actually want it to be slightly higher in the middle, not the edges! I sanded down the lip just a hair and scuffed the whole surface.

So far it's running smoothly (and the belt is closer to centered on the tensioner). The puddles have receded... will keep the breaker bar and 15mm socket in the truck though