Based on some of the statements people have made here, and on other forums as well, there seems to be some misconceptions regarding turbo "seals". They are not seals in the sense that there is rubber on them like what you find on an engine. They look just like piston rings. There is one on the thrust collar behind the compressor wheel, and another just forward of the turbine wheel on the shaft. There is no component of this type of seal to actually "blow", however, the end gap is important in oil control, just like...well, piston rings.
Certain conditions can cause failure of the turbo and its components. One such condition is an overspeed of the rotating assembly. Typically, an overspeed wipes out the journal and/or thrust bearings first. An example of an overspeed would be running a turbo at a higher pressure ratio than the turbo can safely attain.
If the journal bearings fail, you end up with excessive side play, potential compressor or turbine wheel contact with an end housing, and often errosion of the centerbore of the journal housing (It may help you to think of the cylinder wall in an engine). From this, you will eventually end up with excessive gaps in the piston ring seals. This will allow engine oil to be displaced into either the exhaust system or the charge piping/intercooler.
In the case of the thrust bearing failing, the rotating assembly is now free to move fore and aft in the center bore. This excessive movement has a very similar outcome to the journal bearing failure, but often the damage exceeds that of a journal bearing failure. This is because every component of the rotating assembly is effected when the thrust bearing fails. There is also a higher likelyhood of both compressor and turbine wheel being destroyed with this type of failure.
Certain conditions can cause failure of the turbo and its components. One such condition is an overspeed of the rotating assembly. Typically, an overspeed wipes out the journal and/or thrust bearings first. An example of an overspeed would be running a turbo at a higher pressure ratio than the turbo can safely attain.
If the journal bearings fail, you end up with excessive side play, potential compressor or turbine wheel contact with an end housing, and often errosion of the centerbore of the journal housing (It may help you to think of the cylinder wall in an engine). From this, you will eventually end up with excessive gaps in the piston ring seals. This will allow engine oil to be displaced into either the exhaust system or the charge piping/intercooler.
In the case of the thrust bearing failing, the rotating assembly is now free to move fore and aft in the center bore. This excessive movement has a very similar outcome to the journal bearing failure, but often the damage exceeds that of a journal bearing failure. This is because every component of the rotating assembly is effected when the thrust bearing fails. There is also a higher likelyhood of both compressor and turbine wheel being destroyed with this type of failure.
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