Belt derails

[Accx4]

Belt came off. I replaced it and it came off again. I noticed that the forward edge of the tensioner pulley (toward the front of the vehicle) had no edge ridge on it and it was walking off pulling the belt to the outside grooves on the harmonic balancer.

Replaced the pulley on the tensioner and the problem continues. It appears the only pulley not in alignment is the tensioner pulley. Everything else lines up just fine. The tensioner spring still works it just appears the pulley should be about an inch further rearward to keep everything aligned. How can this be? The new pulley I put on is identical to the broken one. Any thoughts? Hate to have to remove the tensioner completely only to find the replacement to be the same. All pulleys on all other components line up.

 

[J_C]

I suspect it is just as simple as replacing the tensioner, that the bad tensioner is what broke the pulley and should have been replaced already.

It's not just that the spring still works, but that it has the correct tension and alignment.

Is this the original factory tensioner? If so, it was due for replacement by now. If not, what make/model and how long did it last?

 

[Accx4]

I suspect it is just as simple as replacing the tensioner, that the bad tensioner is what broke the pulley and should have been replaced already.

It's not just that the spring still works, but that it has the correct tension and alignment.

Is this the original factory tensioner? If so, it was due for replacement by now. If not, what make/model and how long did it last?

I'm over 215k on the original. Weirdly random thing to happen as I was heading up to the gas station from home. I guess I should be glad it didn't leave me stranded somewhere

 

[J_C]

Things wear out. Not so much random as good for it to have lasted as long as it did.

 

[Accx4]

Things wear out. Not so much random as good for it to have lasted as long as it did.

Just don't know why it is so far out of alignment it is solid no wiggle etc

 

[Pete Deering]

Belt came off. I replaced it and it came off again. I noticed that the forward edge of the tensioner pulley (toward the front of the vehicle) had no edge ridge on it and it was walking off pulling the belt to the outside grooves on the harmonic balancer.

Replaced the pulley on the tensioner and the problem continues. It appears the only pulley not in alignment is the tensioner pulley. Everything else lines up just fine. The tensioner spring still works it just appears the pulley should be about an inch further rearward to keep everything aligned. How can this be? The new pulley I put on is identical to the broken one. Any thoughts? Hate to have to remove the tensioner completely only to find the replacement to be the same. All pulleys on all other components line up.

View attachment 444295

View attachment 444296

Check the crankshaft pulley

 

[Accx4]

Check the crankshaft pulley

What am I checking there?

 

[Pete Deering]

What am I checking there?

Grab the pulley, see if it moves in and out. The pulley separate from the center.

 

[Accx4]

Still not up and running. I haven't been able to locate the cause. The tensioner arm on this engine has the pulley facing the rear of the engine and the tensioner arm on the forward side. I am not sure what direction the belt rotates ( I am assuming clockwise) but the new belt seems to derail toward the radiator and depending on the rotation, it either comes off the harmonic balancer first, then the tensioner (if clockwise) or the tensioner first then the harmonic balancer (If counter clockwise). Either way, the belt tries to roll off the front side of the harmonic balancer and the tensioner pulley ( between the pulley and tensioner arm. I removed and reset the tensioner arm. The harmonic balancer doesn't look damaged and is not loose in any way. Thoughts? The previous belt melted rubber into all of the grooves on the grooved pullies which I then had to scrape out the races. I removed the smooth pullies and ran them across the wire wheel on the bench grinder to clean those up. I am just stumped. Thoughts?

 

[C420sailor]

If everything is aligned but the tensioner, you need to look hard at that tensioner. The belt blocks the view. Is it installed properly? Is it the right one? Maybe go to a parts store and compare it.

Something is up with that tensioner assy if it’s that far forward relative to the others

 

[donalds]

Take a pic for us so we can see what u see

A few pictures

 

[Accx4]

Ok... so I was under the truck today looking at the belt route from a different angle and it dawned on me to start looking at parts diagrams rather than belt diagrams and I saw a couple images that surprised me. Apparently the belt may be designed to ride on the forward most pully on the harmonic balancer. This has been happening as I start the truck and the belt rolls forward. It is where the belt actually wants to ride. But... the tensioner pulley rides slightly toward the rear edge of the outside pulls grooves of the harmonic balancer. Is there supposed to be a front edge lip on the balancer to keep the belt from continuing to move forward toward the fan? Mine does not have any front edge... now I am interested again...

 

[EB4X]

This 4.0 ohv (same engine as yours) has a lip...( I might take a pic of mine too)
H BALANCER LINK
I didn't read through all of your initial post....did you just purchase this vehicle? ...so there's a change the prior owner installed an incorrect H.B. ?

 

[Accx4]

This 4.0 ohv (same engine as yours) has a lip...( I might take a pic of mine too)
H BALANCER LINK
I didn't read through all of your initial post....did you just purchase this vehicle? ...so there's a change the prior owner installed an incorrect H.B. ?

I've had the truck for years. It just started spitting the belt off the tensionerand throwing it on the ground. I've seen a couple photos of the belt running on the forward most grooves photo attached. These grooves are barely the width of the belt and feel like rubber though.

 

[Turdle]

I think your harmonic balancer has failed.

 

[J_C]

If everything is aligned but the tensioner, you need to look hard at that tensioner. The belt blocks the view. Is it installed properly? Is it the right one? Maybe go to a parts store and compare it.

Something is up with that tensioner assy if it’s that far forward relative to the others

How did the topic move past this assessment? No matter whether the harmonic balancer is bad or not, the tensioner is supposed to line up with the other pulleys too. It sure doesn't look like it does based on the first pic in the opening post.

The back of the tensioner appears to be keyed. Was it rotated until that keying allowed it to sit fully flush against the mount? I would guess this might be the problem... along with possibly incorrect belt tension resulting from that.

 

[J_C]

I've had the truck for years. It just started spitting the belt off the tensionerand throwing it on the ground. I've seen a couple photos of the belt running on the forward most grooves photo attached. These grooves are barely the width of the belt and feel like rubber though.

View attachment 445173

Okay I may have a better understanding and what it looks like is the harmonic balancer failed, and that pulley pictured is supposed to be ON that rubber portion the belt is now riding on, that you're not supposed to see the side of that rubber at all because it's inside the pulley - until it failed and the pulley shifted backwards.

Now I wonder if the two issues are combined, that a misaligned tensioner caused excessive heat and along with the belt, caused the balancer to fail... or at least speed up its demise considering its age.

* I reserve the right to be wrong.*