Belt stretching issue

[=STAT!XXX=]

So I put a Bomz underdrive pulley on my 90 Legacy L 2.2 non turbo, not really for the performance aspect of it but because it cost 1/4th of a new crank pulley. Anyhow, I had to put a smaller belt on since it's an underdrive, and the belt stretched out so far in 2 weeks that I ran out of tensioner. I got another of a different brand, and got the same result. The belts seem nice and tight upon install, but after a couple weeks they are completely floppy and won't tighten up. Could this be a result of the aluminum pulley transferring too much heat to the belt? Any ideas why this may be happening?

[Wiscon_Mark]

Get a Mr. Josh lightened pulley instead of messing with underdriving. Ever run out of power steering? It's not fun.

[GrassyKnoll]

Eh, my underdrive has been fine. I am going to guess that your problem isn't stretching belt but in fact could be your tensioning screws. Do you know that every point of contact with the belt has an adjustment? If one is a little loose, it might be slowly losening over time. Just keep in mind that there are MULTIPLE tensioning screws.

[ivwarrior]

Are you sure you're not over-tightening the belt?

Oh yeah, and I'd go with a lightened pulley over an underdrive, too.

[=STAT!XXX=]

Just a quick update: after the 3rd belt I just ended up buying an OEM crank pulley, problem solved :)