Bolt the cam blocks on, undo the pulleys so that they can move. Line up the mark on the bottom pulley then put the belt over whilst trying not to move the bottom pulley. Then fit the tensioner, check the front run of the belt is tight, as you need all of the slack in the back run of the belt. Then set the tensioner to the correct tension and tighten the pulleys.

You have to make sure that the engine only turns clockwise (when looking at cambelt end)otherwise you will end up with slack in the front run of the belt which will put the timing out. Then when you are sure it all lines up take the blocks off, rotate the engine again clockwise 2 revolutions until the bottom mark lines up then check the blocks will refit.

if you go past the mark, don't try and turn the engine backwards as it will upset everything, go forwards another 2 turns.

Its quite difficult to explain, you should see what i mean when you are doing the job.