It is certainly possible for competent engine repairers/rebuilders to repair even severely damaged crankshafts because all crankshafts are designed with a "remanufacturing margin". In practice, this margin allows for the journals to be ground to up to a millimetre smaller than what their diameters were when the crankshaft was new.
However, whether (or not, as the case may be) any given crankshaft can be repaired largely depends on three factors, these factors being-
- The degree of damage to the journals; in severe cases, grinding out the damage may result in the journals being below their minimum allowable diameters
- Whether the crankshaft had been repaired before; if so, the journals may already be at their minimum allowable diameters
- The steel alloy the crankshaft is made of; in many cases, especially on severely damaged older crankshafts, it is possible to reduce the bearing journals to their minimum allowable diameters and then to build them up again by a specialized welding process. Even if some damage remains, the welding process “seals” the damage, and subsequent grinding, polishing, and simple heat treatments can restore the journals to their original OEM specifications. However, with many modern steel alloys, the welding process destroys the crankshaft's hardness and wear resistance, and the specialized heat treatment required to restore the crankshaft's wear resistance to OEM-specified depths is so expensive and time-consuming that it is often more cost-effective to replace a damaged modern crankshaft than to attempt repairing it
It should be remembered though, that in all cases, crankshaft repair is a highly specialised area of engine repair that requires the use of specialised equipment, having expert-level knowledge about crankshaft repair procedures, and possessing technical skills that take several years to acquire. Therefore, if you suspect that the crankshaft in your car may have been damaged, we highly recommend that you seek professional assistance from suitably qualified and experienced engine repairers/rebuilders with assessing whether the crankshaft can be repaired and if so, to repair it to OEM- specifications.