Have had a discussion with a friend this week about head bolts and thought that some of you might be able to shed some light on the question.

One time I was replacing the head on my engine and experienced a strange thing.  When I tightened the head bolts to the correct torque, and then removed the tension, the bolts would untighten on their own.  They would move.  The friend said that he thought that this was due to the fact that head bolts stretched and should always be replaced when replacing the head.

Anyone have any thoughts on this?
George