Does he bite during play? If so, when he bites you, make a high pitched squeal noise or say "Ouch!" in a high pitched tone. He should looks startled and stop. If he continues, make the noise or say "ouch!" again and turn your back to him and stop play.
The high pitched tone is to mimick a puppy squeal when it is hurt. When he was playing with his littermates, they would have done the same if he bit them.
Dogs hate being ousted by their pack. By physically turning your back and stopping play, he will learn to associate a bite with no more play!