you have to undo the bottom pulley so you can see the timing mark on the crank sprocket - i think these are what you mean you struggled with in the past, they are not generally that hard to get out though.... few ways to stop the engine rotating as you undo the bolts:
-you can just stick a screwdriver through one of the gaps in the pulley and then you can wedge it against the engine while you undo the 3 bolts.
-Or put the car in gear and get someone to press the brake, this stops the wheel turning which in turn stops the gearbox turning which in turn with it in gear will stop the engine turning.
-Or you can wedge a big screwdriver in the teeth of the flywheel to stop it turning.
I usually go for the first of them as i'm normally on my own
the sensor there, the crank sensor, you don't need to touch that at all...
once that pulley is off rotate engine from the crank until the timing marks on crank and cam both line up, undo the tensioner and remove belt, double check the timing is lined up before you fit the new belt - i have seen countless cars with the timing out a tooth. Whack your new belt on, cam first then down round the waterpump, then crank then tensioner. Tighten tensioner, check timing marks, rotate engine (from crank not cam) 2-3 times and recheck timing marks. Assuming its ok refit the bottom pulley taking care to put it the right way, little pip on the sprocket in the little hole on pulley. Refit belt cover, aux belt, inner arch liner, wheel etc. Job done.
Its as Charlie says, exactly same as a cento 1108 engine but on the punto you have way more room making this whole job much easier and less fiddly. I would say the hardest part on a cento is getting the belt cover off and on but no such problem on the punto.
