cam belt problems

[s13eater]

anyone had a cam belt that has tried to come off ? i put a new one on yesterday and followed the tentioning from the manual, 2 turns of the crank pulley to tention.i did this 3 times but it still tried to come off, so i refitted the old one which, now its fine, the old one has only been a year, but i thought i'd change it before i went on holiday, i think there's something up with the new belt.