Thanks guys for the feedback. The leak is at the valve seat. We were putting air in the cyl. to hold the valve up while we changed the springs. When the torque on the head bolt next to #6 exhaust port goes over 50 lb. it will start to leak. The block and head have both been milled. The head should definately be mag. checked to make sure. We have even bolted it to another block-same. He had another head with only the bosses removed and nothing else done to it. We bolted it to two different blocks and got the same results-leaks at valve seat. Thanks again guys.
