It's not prohibited, but it never ever means what past tense in English does. Tense in Japanese subordinate clause is (basically) relative to main clause, so if you bought a book and the book was heavy, you just have to say .
suggests the book was heavy before you bought it. But there rarely are books that being sometimes heavy, sometimes light, like King Arthur's sword. A more likely setting is that you bought that book on the premise that it was heavy, for example:
> You went into a bookstore. You took books in your hand. This book was light. This one was light too. Oh, this one was heavy. Thus, you bought it.