Main bearing cap broken how to repair

I sometimes take mild chances with engine abnormalities if I can see it will not effect things, but I would be hesitant to run without that repaired. There is a fair amount of torque that is transmitted to the pump at higher RPM's especially, and the recess there indexes the pump in place. If it shifts even a small amount, it will put abnormal side force on the pump shaft, the through-block bushing, the pump shaft gear and the cam gear.

If you do run with it as is, the good thing is that the pump portion that fits in that recess will be trying to shift to the right in the bottom picture, towards the rear crank throw as it reacts to the pump shaft torque and the 2 bolts. At least there is some material left there, but it is not very well supported with the side broken out. Any repair of that area will mainly be under tension.

Silver solder does not seem adequate, IMHO. Ideal, you'd braze it, or use some other low or no pre-heat process; IMHO brazing should be adequate for the forces involved. Then have the main block bore with cap torqued in place rechecked for true roundness.

There looks to be too little material around the cap casting to put a bronze bushing in that area. Any epoxy on the surface of the break will be under tension with the way the forces work out, so would have to be pretty thickly laid over the surface to have any chance to work.

This thread has an interesting video with nickel 99 rods...."No-PreHeat" Cast Iron Repair Technique - Miller Welding Discussion Forums