After trying a number of very good sealants and alot of patience I gave up on the idea of the press fit ever holding. Every time after a few weeks it always started to leak. So I snatched it out AGAIN and proceded to tap threads into my head. The cast iron head only has a 3/16 in. thick water jacket and is barely enough to get a thread and a half taped into it. I cut a 1in. nipple down to 1 1/4 in. long leaving about 3 threads and welded a thick washer onto it where the threads tapered out. I used a die grinder with a sanding pad to prepare the mating surface on the head. I wrapped the threads with teflon tape and cut a gasket to fit over the pipe nipple and to fit up to the washer, sealing it to the mating surface on the head. It works like a hollow drain plug on an oil pan. It worked PERFECT! Sealed great with no leaks and I dont have to worry about it blowing out EVER!! Problem solved!
