Heat the block around the bolt and hammer on the head. Not so much
hammering that you damage it but enough to break loose the rust some.
If you have to dril it out start with a small bit and try to get as
exactly in the middle and drill as straight as possible. Then work up
the drill bits sizes.

wrote:
I have an issue with a bolt on one of the cylinder heads on one boat
engine I have. I need to swap cylinder heads on the boats, and the
donor boat is fighting me tooth and nail.

The problem is that 1 bolt will not come off. It's towards the bottom
of the engine (I had to take off part of the engine cover part) and no
matter what I do (vice grips, socket, soak it with liquid wrench)
nothing will budge this thing.

Any suggestions? I can provide pictures to better explain where the
bolt is.