Hey guys. I have been having issues with my serpentine belt jumping off of the tensioner pulley ever since I replaced the belt after I replaced the water pump. The old belt was getting pretty dry rotted so I went ahead and replaced it while I had everything off. The new belt squealed and I figured it was the tensioner pulley. I put a new pulley on and it still squealed however it jumped off a little and rode on the ridge of the pulley which then split the belt in half. I got another belt and gave it another try. This one didnt squeal but same thing happened. It jumped off and shredded to bits again. So i put the old pulley on and got another belt. This one doesnt squeal and it hasnt jumped off yet but I am concerned as it does ride really close to the edge of the pulley. It almost looks like the pulley's angle is off or something. The belt is more centered on the side that is closest to the power steering pump. The side towards the alternator is almost touching the edge. Any ideas on how to fix this? Would replacing the tensioner maybe solve the problem? I really have no idea on what to try next. Thanks.

 

Align all the pulleys, there are several methods to do that, including using washers, return the tensioner pulley and replace it again, check if the belt size is the one you should be using. With the belt off, turn each pulley, look for noises, vibrations, or stuck pulleys.

 

For some reason the 4.9 seems to be more prone to this problem than most other engines. Dunno why exactly, but if everything is right there's not a problem, so something is indeed wrong on your engine. I think the biggest culprit may be the tensioner. Not so much the idler pulley (which you've apparently already replaced), but the tensioner itself. If it gets worn and twists just a bit, it's going to send the belt off at an angle.

The Motorcraft tensioner seems to be a much better unit than the after-market parts you'll get at most chain stores. It gets bonus points for having a 3/8" square fitting at the top, making it much easier to rotate with a 3/8" drive breaker bar or ratchet.

Replace the tensioner and I bet your problem goes away. So far that's fixed it for me.

 

On my 4.9s I usually bite the bullet and buy the Goodyear belt and use a scotch pad or light sand paper to clean up the pulleys.
Regards
rikard

 

So I ordered a brand new entire tensioner assembly from Motorcraft and the belt is still riding off the side towards the engine. The pulleys appear to be lined up correctly. It has a brand new alternator and power steering pump which it is in between so I am lost

 

The belt is new, so it wasn't the cause. You replaced two parts, you should look at these two, you think they are aligned but I can bet you it's either the new alternator or the pump which are causing the problem. I would look specially hard at the steering pump pulley, it probably isn't all the way in.

 

I pulled the power steering pulley out a little because of the side it slid off was the closest to the engine. It seemed to help some however the belt still rides close to the edge on the side that it enters the tensioner pulley from the alternator. There is a little bit of gap where it leaves towards the power steering pump like it should be. I have no idea how to get it lined up now. I dont see a way to adjust the alternator pulley

 

Also I replaced those parts before I was having belt problems if that helps

 

Sorry to hear that wasn't a solution. Now you've got me concerned that I may still have a problem given that your symptoms matched mine pretty much exactly.

Have you taken the tension off and made sure none of the pulleys have any play?

 

Yeah I checked them all and they are all snug. The only thing I can think of is somehow the angle is off on the tensioner pulley being that the belt meets and leaves the pulley at an angle.

 

I just wanted to suggest an idea. I have no assumptions it has been suggested or tried. Find yourself or buy, a good straight piece of aluminum or steel. About 1/4" thick, 1" wide, 2 maybe 3 foot long. Use it as a straightedge to check against the crank/balancer and corresponding pulleys. I used this suggestion to align my alternator and power steering pulley when I had to replace both, with the power steering pulley being the culprit.

I also have seen this a problem with the 4.9 engines shredding belts or becoming mis-aligned and squealing. This idea may or may not help you. I hope it does though.

 

That was precisely my assumption as well, with the thinking that the tensioner was worn in some way and tweaking itself off-angle a bit, thus sending the belt off at the wrong angle towards the power steering pulley.

Does your idler pulley have the belt retainers so that the belt can't go beyond the surface of the pulley? I don't know if that really makes a difference, but mine does.

Given that you've replaced the tensioner with a new Motorcraft unit, I think we can rule that out and focus on the power steering pump. Assuming you've got the pulley installed all the way on the shaft, perhaps it might be worth shimming the pump inbound with some thin washers. The other thing to consider is re-seating the bolts for the bracket, making sure the assembly is being pushing towards the rear as the bolts are tightened. I don't recall if there's some play there.

 

Ok since I adjusted the power steering pulley, the belt seems to have settled a little and now appears to have the necessary clearance on both sides now. It's not center of the pulley or anything but it does clear and hopefully it will settle on in. Thanks for all of y'all's help. If anything else happens ill keep ya updated

 

Of course, when you modify something and a problem rises you always have to look first at the latest modifications you made. I'm glad it's working better.

 

In my case, after 3 changes of the tensor with a broken screw, I found out that I had a mising screw, on the aluminium Base that holds the Alternator, the tensor and the smog pum. (Bronco 93 302 EFi motor with AC). A second screw was loose, "so my mule was working on magic & hope " dam with the mecanics if you want some thing well done do it yourself. I eliminated the Smog Air Pum and re-routed the belt but I steel have the squeal sound from time to time especiali in my AC its On Tomorow I am gone put the Air Pump Back but firt i am wone too turm it apart and eliminate any thing but the pulley.......
Smog Pump its back ( wat is left of it) paid 20$ to have it empty and install new bearings.
re instal my old 100" belt and now every thing its working fine. (I am using the self rebuild tensor)