Cam belt is on, poly belt fitted and nothing has gone 'bang' so far (tightly gripping a large chunk of oak, specially kept for the purpose of superstition).
One possible 'rule of thumb' for belt tension might be the force needed to rotate the tensioner pulley by hand. Could someone try this on a (properly) tensioned belt and report back please? It takes two finger and two thumbs to turn my tensioner pulley now, against the tension/friction of the back of the belt. This after turning the cam sprocket back a fraction to release pressure from valve springs etc.
Anyone planning to change an S40D cambelt, particularly on a pre-2000 car, should take a look at
http://www.gates.com/europe/ Click on tech bulletins and select bulletin #17. If you want to feel lucky, take a look at bulletin #19 (same engine for Renault) - there are about ten different belts!
Bill