Process for reducing cracking in superalloy metal components by selectively growing large single grains during the casting operation at a region where fusion welding will be required. In a generator chamber, a shielding rib is provided which is disposed between a generator and an oil introduction port in side view and which extends skewly upwardly from the oil introduction port in a manner so as to cover one end side of the oil introduction port. The inner shield includes a deflector rim disposed proximate one of its ends that is configured to absorb the energy of ejected material, in the highly unlikely event of a flywheel failure during testing.