Re: 1964-1972 Mercruiser water in oil and in # 4 Cylinder
Make sure you rotate that block by hand a few times with the head off and make sure all the pistons all come up to the top and that everything moves OK. Depending on how much water was pouring into the cylinder on the compression stroke it may have cracked the cylinder wall or bent a rod. Look down in each cylinder and make sure they look good as well.
I recently had the same problem with a manifold rotting out on a 5.7L v-8. luckily there was no major damage, water must have been pushing by the rings or something to get into the oil.
I've had the head off, and the pistons, cylinders etc. all look really good, took the side valve cover off to check for cracks (all good) I'm hoping new gaskets and replace the riser/elbow will cure this thing.
It belongs to a super nice older fella, he and his fishing buddy are ready to get it back, and I really want it to be in excellent shape.