I don't see the bolt itself being the problem, but rather the forces being pulled through the bolt into that short of a thread engagement in the casting.
See, the first 1-1/2 female threads in the casting are going to provide almost no strength: they are half-cut, if that, and the typical hole begins slightly oversize at the opening. The first 1 to 1-1/2 male threads on the tip of the bolt are also understrength - since they are also not fully cut, so they won't engage fully into the female threads of the casting.
Net result is increased stress in the few engaged threads in the casting, right at the point where the stress from the entire bolt is trying to "pop" the casting metal out.