peugeot use a special tensioning gauge. measured in units called seems. should be 98 seems to pre tension new belt. tighten up 6 bolts on cam and diesel pump pulleys, and check bolts are in middle of slots always. turn engine over by hand twice then undo 6 pulley bolts, tension to 54 seems,tighten 6 pulley bolts, then remove tension tool then refit should show between 51 and 57 seems.turn over twice by hand and check timing marks align. think only main dealers will have this tool. only way without that is to guess the right tension. remember the 6 bolts on cam and pump pulleys should be loosened whilst fitting new belt and tightened up after.
me, June 2009