Had this same issue on a 60' grain/bale elevator because both drive sprockets have to be exactly in alignment to drive the chain/flights. The cast keyway were wallowed out. The metal shop guy machined a 5/16" hole through the cast iron sprocket & 1" steel shaft & installed a cotter pin. Worked great.
I would just put a dollop of weld metal on 3 or 4 sides of the hole, then ream it to the rods diameter. Given the choices of weld metal available today, that'd probably last longer than I will live, and maybe longer than my kids too.
Had this same issue on a 60' grain/bale elevator because both drive sprockets have to be exactly in alignment to drive the chain/flights. The cast keyway were wallowed out. The metal shop guy machined a 5/16" hole through the cast iron sprocket & 1" steel shaft & installed a cotter pin. Worked great.
I would just put a dollop of weld metal on 3 or 4 sides of the hole, then ream it to the rods diameter. Given the choices of weld metal available today, that'd probably last longer than I will live, and maybe longer than my kids too.