Find the ends of the crack and drill a 1/8" or smaller hole all the way through to prevent the crack from continuing to spread. We also used to use overlapping threaded tapered cast iron plugs for crack repair, a process called "sewing". The plugs and the tapered taps for installing them are available on Ebay.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!