You said "the water pump and alt are new".  Already that makes one
suspicious that one of the two is causing the problem.

I put a rebuilt alt on my '85 that didn't turn as smoothly as it should.
  It ran hot and failed in short order (replaced under warranty).

Either one of the two components is bad ... or, as others have pointed
out, one of the pulleys is bad or misaligned, or the alt bracket bolts
down low at the engine need attention.

Good luck with it.

Mike
'84 GL 7 pass
'85 GL Westy

Oliver Balson wrote:
>  Hello vwers,
>
> I'm having a little trouble with an engine I just put in my 91 carat -- in just a few weeks, I seem to be going through alt/wat pump belts.  With the belt properly tightened, it just takes a few days before the squeal begins and a couple more days before the belts loosen up and slip off (twice the car has overheated to find the belt totally flipped over and loose!), After retightening, the process begins again.  Each time it sems the belt is stretching out excessively, as the alt. hasn't slipped.  I've tried 3 different belts and know they are tight enough to begin with.  The water pump and alt are new, so no drag from either end of the belt, and no apparent wear on the belt.  Anyone have any suggestions?  Just don't know what to do next.
>
> Thanks, Oliver
>
> 90 westy -- Gretel
> 91 carat -- Hansel
>