While "sewing" is the most effective fix, you can use a good quality epoxy, like Devcon Epoxy Steel if you get the surface of the block good and clean. J-B Weld doesn't seem to work as well as Devcon. Find the ends of the crack, and "stop-drill" it to prevent it from growing. Just drill a small hole at the end of the crack, and peen a piece of welding rod into the hole to seal it up. Then take a Dremel tool or an air die grinder, and clean the block surface down to shiny metal. Mix up a small batch of the epoxy, and work it over the crack to a thickness of about 1/4" or a little less. Just before it cures, press a piece of 40 grit sandpaper over the patch and lift it off carefully, and it will take on the appearance of cast iron, effectively hiding the repair. A little spray engine paint, and you're good to go!
Jerry
