What I did on my engine when I found this same problem was to grind out the crack as far down as I could. Then I magnifluxed the crack so I could find the ends of the crack. I then drilled a small hole into the ends of the crack so it would not keep going. Then I use a wire feed welder with .035 stainless steel wire and a tri-mix gas. That is Co2, Argon, and Heilum. I also installed a stud in the hole so as not to plug the hole with weld-metal. I then welded the crack and then using a chipping hammer I beat the weld to relieve the stresses. I let it cool and then put the engine together. It has been running without any problems for just over four years now.