Major Causes of turbo damage
Major Causes of Damage:
Most turbocharger damage can be traced to one of a few basic causes:
- Lubrication Related Problems
- Foreign Object Damage
- Operational Temperature Extremes
Careful examination of the parts from a damaged turbocharger and proper interpretation of their condition will usually pinpoint the cause of a unit´s problem. If a turbocharger is ruined by an external fault and that fault is not found and corrected, the replacement unit will soon fail in the same way as the original.
Lubrication Related Problems:
Lack of proper lubrication can ruin a turbocharger within mere seconds of operation. With shaft rotation speeds approaching 200,000 rpm in some models, all bearings must receive a supply of oil that can stabilize, lubricate and cool. When lubrication is slowed, stopped or interrupted for any reason, metal to metal contact first occurs at the journal bearings/shaft journals/bearing bores of the center housing. Without the oil, friction will generate enough heat to turn the shaft and/or thrust collar blue (This bluing is often not as evident in units with liquid-cooled center housings.) The thrust bearing, thrust collar and/or backplate mating surface will also show signs of damage. Once the bearings are damaged, "shaft motion" increases. Instead of rotating in a perfect circular motion, the shaft begins to orbit. As bearing clearances are enlarged, shaft motion becomes more intense, and damage accumulates. The center housing seal bores, shaft hubs, and thrust components (thrust collar, thrust spacer, and backplate assembly/thrust bearing, as applicable) are damaged next. This additional damage, in turn, allows for more violent shaft motion. After shaft motion reaches a certain point, the turbine and compressor wheels will contact their respective housings damaging the blades and possibly backing off the shaft nut. When blades are damaged by housing rub, the precise balance of the wheel/rotating assembly is destroyed, leading to even more shaft motion. The shaft may eventually break from a combination of motion stress, fatigue and destabilization (due to the original problem, insufficient lubrication).
Foreign Material In Oil:
Foreign material in the oil includes various sizes of abrasive particles, corrosive chemical compounds, and dilution by coolant or fuel. Foreign material in the engine lubrication system first damages the journal and thrust bearings. When foreign material in the oil is found to be the primary cause of damage, steps should be taken to identify the foreign material or eliminate its entry into the system.
Fine abrasive contaminants will score and wear virtually every bearing surface . If material particles are large enough, the contaminate related damage is more confined to journal bearing outside diameters and center housing bearing bores because centrifugal force keeps the contaminants away from the spinning shaft.
Corrosive chemical compounds alter surface finishes and clearances. When surface finishes are too rough, oil films are penetrated allowing metal to metal contact.
Diluted oil has its film strengths reduced and does not easily adhere to surfaces. The lack of surface adherence does not allow the shaft to be dampened and supported by its encompassing oil film.