FWIW... I don't have a Zetec, so I don't know, but can the belt be put on more than one way? I know I had a serpentine belt on an old van that you could put it on 2 different ways. One way it would tighten up as it should, and the other way it would just barely be tight if the adjuster was all the way out.
I too prefer Gates parts, but it doesn't seem like anyone is making things to last. However, your problem seems to be worse than that. I think you should look into whether or not that belt is too long, or what position the tensioner is in when it's all the way tight. Like AMC said, the arm shouldn't be close to or touching the tensioner stop.
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Originally Posted by the user formerly known as ZX3_Chick
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