[paweldor]

For that repair I'd use AllState 4-60 Nickel rod. Best cast rod I've ever used to repair stuff like that. 3/32" size.

You are going to dismantle the motor, aren't you? You might get lucky welding it assembled, but the innards have to be protected real good from any arc spatter. I'd only weld that in the FLAT position, hence the concern about screwing something up internally.

After dismantling, bevel the cracks at least 1/2 the thickness of the web. If crack isn't all the way across the web, do as Sam said and "stop drill" the ends of the crack.

Preheat, and weld intermittently. Don't weld all the cracks at once. Weld one and allow it to cool to a point you can lay your hand on it. Weld a little more, repeat. Peening the weld bead between passes will help relieve welding stresses also. Cast Iron has virtually no ability to stretch (ductility) as the bead cools and shrinks. This is where most cast iron welding repair failures occur, along side the weld at the heat affected zone. Welding all the cracks at once could really warp the housing, and your armature won't spin properly. If it's possible to clamp the webs to prevent distortion, do so.

I once had a large HP electric motor housing cracked in a shop I ran in Korea. Took one of my Korean weldors almost a week to do the job, using the weld a little, cool a little method. Like I said, it was a humungous motor, very expensive to replace.

Good Luck.