Turbochargers - Causes of failures
The following fault list was created based on our experience acquired during turbine remanufacture. They are only some selected examples of damage. The level of some faults is complex and requires precision measuring equipment for proper verification. The listing should only be treated as informative as the simplest examples of failure.
The consequences of bearing damage
Damaged bearings strongly contribute to increased rotor clearance and lack of balance. As a consequence, the compression wheel can be rubbed against the aluminum shell or turbine rotor by a cast iron collector, and then the rotor is bent and broken. In extreme cases, turbocharger cracks and compression wheel blocks, as well as other turbocharger elements. On photo below there is severely damaged compression wheel due to collision with aluminum compression shell. Next photo shows the result of increased clearance between the bearings and the rotor, as well as bearings, and bearing housings, the rotor blades have been impacted by a cast iron body.
Too low engine oil pressure or insufficient oil pump flow causes semi-friction, thus increasing friction between the bearings and turbine rotor. As a consequence, the rotor rotates at a lower rotational speed, which in turn reduces the flow and significantly reduces turbocharging and engine power. It is also important to notice the working temperature of the bearings and the rotor, which is prone to seizing this pair of precision. Long operation of the turbocharger in such a state will lead to further faults, including a change in the structure of the material and the rupture of the turbine rotor.
On pictures below: On the left the superheating zone of the turbine rotor was caused by insufficient lubrication. On the right blotting of the bearings caused the turbine rotor to break.
Excessive oil change intervals or improperly selected oil and switching off the engine warmed up immediately after stopping the vehicle may result in the build up of the carbon deposits in bearings. As a result of the residual coal deposits, the bearing is rapidly destroying and consequently the entire turbine. The presence of other diluted oils in the engine oil, such as coolant or diesel, is unimportant.
Below is highly carbonated bearings against of the new thrust bearing in the back.
Second photo shows almost completely blocked oil output pipe from the turbocharger which led to its destruction.
An inefficient flow of oil through the hose leads to the loss of proper lubrication and cooling of the turbocharger. As a result of the flow blockage, the oil is vented through the sealing rings leading to the turbine leakage. If it occurs on the hot side, the carbon deposit will be generated and will have affect on the wear of parts such as bearings, housing, sealing rings and rotor. On the photos there is overheated turbine rotor and accumulated deposits. It was caused by a leaky sealing ring on the exhaust side. On the right there is failure of the bearing housing due to overheating of the turbine exhaust side seal ring.
Presence of foreign bodies
As a result of entry of foreign matter from the engine intake or exhaust system, many turbine breakdowns occur after contact with foreign material with high-speed turbine components. In the case of components from the intake system, these are parts of the air filter housing, the filter itself, or the mounting straps. When the foreign body enters the exhaust side of the turbine, it is most often a fragment of a valve, a piston ring, a piston itself, or a broken piece of a glow plug. Destructive effects are also felt from the combustion chamber of the engine. Engine components are not the only foreign bodies that can damage the turbocharger. In the case of an inadequate intake system, eg with a leaky intercooler or its pipes, unfiltered pollutants such as dust or road salt can be sucked into the compression wheel of turbocharger.
On the left you can see damaged compressed wheel blades due to one-off contact with a small foreign body. On the right - after prolonged presence of foreign bodies in the intake system.
Below on the left is total destruction of the compression wheel after leaving the mounting band inside the intake system after incorrect turbine assembly to the engine.
On the right one of the blades of the variable turbine geometry was seriously damaged after contact with the detached rotor blade.
Below is severely damaged blades of variable geometry after repeated impact of parts of rotor blades whose failure has been caused by excessive exhaust temperature.
On the right there is extremely sensitive geometry blades from the 1.6 HDI engine. During reconditioning, we replace this defective geometry design with full, more resistant blades.
Below is scratched rotor by contaminated engine oil (eg in the presence of filings). On the right high friction on the rotor has led to a rupture. The direct cause was the supply of contaminated oil.
Excess rotor speed or excessive exhaust temperature
The turbine rotary assembly has been subjected to a strict set of parameters. This applies, inter alia, to the range of rotational speed with which the rotating system will rotate. If the maximum speed specified for a given turbine is exceeded, it can be destroyed within a dozen or so seconds. Excessive exhaust temperature can also lead to serious turbocharger failure. The most common cause of this type of failure are:
- Changes to the injection map as a result of tuning
- Blocking of the variable geometry by the carbon deposits in a position with a small gap, as is the case with low engine speed. This results in a lack of pressure limitation at high engine speeds.
- Damage to the electrical system of the vehicle, the electric control of the turbine or the leakage of the pneumatic control system will result in a lack of control over the supercharging pressure
- In the event of a leak on the compression side, the turbocharger will increase its turbocharger speed as it runs at a lower load.
Below is turbocharger after exceeding the permissible speed. The overheating of the rotor blades is also visible. When the permissible speed is exceeded, plastic deformation of the aluminum alloy seen in the form of "orange peel" occurs on the rear side of the compression wheel - see right photo.
Below you can see discoloration and rotor damage characteristic for too high exhaust gas temperature. On the right there is damaged pneumatic regulator, due to corrosion. This is a common failure of turbochargers used in the VW Group.