So I decided to replace the auxiliary belt on my 156 (1999 2.0 Twinspark with AC), since the belt was very cracked and clearly slipping when I had a look.
The new belt I put on is 1970mm long (the old one is 1975mm I think), but it squeals a lot on start up, but soon goes away. Now and then it will still chirp when driving. So possibly a tension issue.
I had a look at the tensioner and its spring is fully bottomed out, as in it can't put more tension on the belt even if I turn it with a spanner. Is that normal? I noticed a little line on the tensioner and two lines on the mount, is that the range of tension I'm aiming for?
There is also a slow clicking noise which sounds like it is coming from the tensioner bearing, so I think it's new tensioner time anyway, but that's not going to help the belt tension...