Dephaser problem 172 cup

[Cup_Clio]

Ok guys i know pracically nothing about this so called dephaser, what it does, how it works, and so on.
After searching through the forum for half an hour i think ive found out what the problem is with my car. Its making a strong tapping noise when ticking over. Ive had problems with it mis firing aswell. Its on 103k miles and is actually due a good service.
so my question is
what is this dephaser thing
where is it.
how to i fix / change it and whats it gonna cost to sort...
Any help much appreciated
Thanks

 

[sideways danny]

the dephaser pulley is on the end of the inlet camshaft. Changing it is a case of a full cambelt change plus a new pulley. There's no extra labour involved in changing the pulley as part of a cambelt change. Latest price on the dephaser is £171 so add that to a belt change (£240 on a cup from me)