This is one sentence and it has : Subject ( A boy) Predicate (verb + object) verb = is ( the second 'is') object = friend If you say 'a boy is named' you are using another predicate in the sentence and that is not possible according to grammar rules. If you want to say ' a boy is named Tim (rather is called ),then you can make it one separate sentence. The boy is called Tim. He is my friend. If you combine them in one sentence ,then you have to use only one predicate ( one verb ),unless you use a subordinate clause as in : The boy ,who is called Tim, is my friend. In short ,a main clause has only one predicate ( verb + object) ,in case of more than one clause (including a subordinate one) each can have its own predicate.

**A clause cannot have two verbs.** (Unless certain criteria are met) The trick is, you need to learn how to break up English sentences into clauses. A boy names Tim is a friend of mine. or A boy, that is named Tim, is a friend of mine. **Notice that each clause has only ONE verb.**