Cinquecento/Seicento cam belt change

if you are fitting a new tensioner and if not why not?
you will need to tension it. there is a 'proper' tool but a piece of steel or the like with 2 M6 bolts at the correct spacing for the tensioner will do fine.
ive not tested it but you may find an angle grinder blade tool will fit as well.

so remove the centre section from the old tensioner and fit to the new one.
loosely bolt the new tensioner in place.

the new belt will have markings that corespond to the timing marks on the engine plus an arrow for rotation.
place the belt on the crankshaft making sure the timing mark doesnt move and the mark on the belt is aligned.
next up fit the belt around the water pump and then up to the camshaft pulley again taking note of the timing markings.
finally fit the belt over the tensioner pulley ensuring any belt slack is by the tensioner.

now adjust the tensioner up to remove all slack from the belt and tighten the 13mm bolt to hold it in place.
the belt shouldnt move more than 90o when twisted at the tensioner.
if its too tight or slack then readjust the tensioner.

refit the crankshaft pulley bolts and alternator belt and tighten up.manually turn the engine over 2 full turns to check everything is aligned and tight.
recheck the timing marks are still aligned top and bottom.refitt the spark plugs if you removed them.

now if you want you can turn the engine over while everything is still off though i tend to just go ahead and put it all together.