If a main- or connecting rod bearing fails, then the crank pin or journal surface may get damaged and may show one or several of the following:
- Bearing material sticking to the crankshaft surface
- Overheating, made evident by black/blue discoloration and, as a consequence, local hard sports
- Dents and scoring on the pin or in the fillet
- Heat cracks
In any of these cases, it will not be possible to just fit back new bearing shells. If new bearing shells are fitted without rectifying the damage to the crankshaft first, then the bearing will quickly fail again and the damage will in all likelihood be more severe.
If the accident has been very severe, then it may not be possible to save the crankshaft. In the majority of cases though, a crankshaft can be saved by machining and/or polishing the pin in order to restore the correct geometry and surface finishing.
QuantiServ is specialized in repairing crankshafts without removing them from the engine. Our highly trained in-situ technicians have over the years been able to save hundreds of crankshafts that would otherwise have been condemned and would have had to be replaced.
If a crankshaft can be recovered by machining it in-situ, then a lot of time can be saved compared to a renewal. In-situ machining is also cheaper and as long as the affected engine is not the vessel’s only propulsion one, the vessel usually does not have to be taken out of service.
It is possible to carry out in-situ machining on crankpin and/or main bearing journals. After the machining, under-size bearings will have to be fitted. These can be ordered from the engine manufacturer or, for most engine types, through QuantiServ. Typically our reliable partners are able to supply under-size bearings if not from stock then within about four weeks at most.
Usually the repair process involves the following steps:
- Detailed inspection of the damage, including all relevant dimensions, NDT testing for heat cracks, checking of the hardness
- Mounting of cutting rings
- Machining in several cuts until the pin surface is free of damages and until all cracks have been removed, if any were present
- Removing the cutting rings and installing the fillet grinding tools
- Grinding of the fillet radius
- Mounting of the cutting rings and polishing machine
- Super-polishing of the surface
- Comprehensive quality check (hardness, dimensions, bearing contact area, …)
QuantiServ has pioneered the in-situ cutting process. Its main advantages are that it is much faster than grinding and that in-situ machining by cutting is possible on smaller crankshafts than by in-situ grinding.
Some of these workshops are also equipped for grinding crankshafts in the workshop, on a stationary crankshaft grinding machine. The largest one of these is located at QuantiServ Singapore’s workshop and is able to handle crankshafts that are up to 6000 mm long.
If, usually following an accident, the crankshaft hardness is found to be beyond acceptable limits, then in-situ annealing might be a quick and economic solution to still recover the shaft. QuantiServ is offering this process and have since been able to save many crankshafts by bringing their hardness back to the acceptable range. The process is described in the In-situ Heat Treatment (Annealing) section of this website.
The above described processes of course do not only apply to crankshafts but to any kind of rotating shaft, such as propeller shafts, alternator rotor shafts, turbine shafts, etc.