Turbo Failures: Causes, Analysis, Prevention

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Turbo Failures Causes, Analysis,
Prevention
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In case of turbo trouble . . .

• Failures of turbos are oftenmisunderstood
• The turbo is blamed when it is broken,
  although it was killed by an engine
  malfunction.
• The turbo is replaced although it is not even
  defective.
• ? Replacing the turbo is not always the right
  answer!

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Most Common Reasons for Turbo Failures

• Bad oil (contaminated, wrong specification)
• Lack of lubrication (not enough oil flow / oil
  pressure)
• Foreign objects (entering compressor or turbine)
• Overspeeding and/or overheating(often due to
  manipulations of the engine or the turbo)
• Turbo repairs not according to manufacturer's
  instructions
• Oil leakage (oil in compressor or turbine
  housing)? In most cases the turbo itself is not
  defective!

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1. Bad oil (contaminated, old, wrong)

• While staying in the engine, the oil collects
  soot, dirt, metal particles, fuel, water,
  combustion products etc.
• This has several effects
• Deterioration of viscosity and temperature
  resistance of the oil
• Accumulation of abrasive particles
• Usual consequences are
• Abrasive wear of bearings ? increasing rotor
  play
• Reduced ability to lubricate ? symptoms of lack
  of oil
• Oil carbonization ? wear of bearings, blockage
  of oil passages

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Worn thrust bearing due to dirty oil
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Journal bearing extremely worn by dirty oil
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Shafts worn by dirt in the oil
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Compressor wheel with rubbing traces
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1. Bad oil (contaminated, old, wrong)

• Lack of temperature resistance? oil starts to
  carbonize at lower than normal temperatures? oil
  carbon slowly builds up on bearing surfaces,
  internal oil channels, seal clearances, and clogs
  them? bearings wear out, oil supply is cut off.
• Preventive action Carry out oil and filter
  services as per OEMs instructions. Use oil that
  is specified for turbocharged engines.

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Thrust bearing with oil carbon deposits
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Bearing housing with oil carbon deposits
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2. Lack of lubrication

• In normal operation, the rotor (up to 250.000
  rpm) and static components are separated by a
  film of oil thickness between 0.01 and 0.08
  mm.
• During rotation, direct metal-to-metal contact
  with the bearings causes
• adhesive wear friction, high temperatures,
  bearing metal transfer ? bronze colour on
  shaft, thrust ring, flinger sleeve
• tempering colours (yellow - brown - blue) on
  steel parts
• and blockage of the shaft, causing the shaft to
  break.

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Shaft with bearing metal due to lack of oil
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Flinger sleeve with bearing metal, lack of oil
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Crack in thrust bearing due to lack of oil
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2. Lack of lubrication

• Failure modes
• Insufficient oil flow rate (1 - 13 l/min) or oil
  pressure (min 1.5 bar under load) ? unstable oil
  film
• Not enough oil in the sump / oil line leakage ?
  oil pump draws air
• Oil with too high viscosity ? slow oil film
  build-up after cold start
• Oil with too low viscosity ? cannot create a
  stable oil film

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2. Lack of lubrication

• Consequences of a) - d)
• Bearing wear ? sealing ring wear ? oil leakage
• increased rotor play ? wheel rubbing
• Or
• Shaft blockage ? Lock nut could loose (only
  possible
• by left-hand-thread)
• Wheels try to rotate ? shaft fracture
  especially when
• oil supply is suddenly cut off completely.

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2. Lack of lubrication

• Preventive action- Use correct oil (observe
  OEMs instructions)- Check oil level regularly-
  Do not apply full load within 30 seconds after
  cold start- Check oil system for defects
  and clogging when a turbo has failed with
  symptoms of oil starvation.

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Turbocharger Speed After Engine Shut-off
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3. Foreign objects enter compressor or turbine

• Compressor side
• Object damages inlet edges of blades. A small
  object can pass through and is caught in the
  intercooler (if present). If not engine
  damage!A noticeable noise and drop of power
  usually occurs.
• Nuts, washers etc. forgotten during engine
  service
• Pieces of intake system coming loose
• Pieces of deteriorated or non-fitting gaskets

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3. Foreign objects enter compressor or turbine

• Turbine side
• Object damages inlet edges of blades
• in most cases the object is found in the turbine
  housing at the end of the volute.
• The damage is not always immediately recognized
  if turbine wheel is still able to rotate.
• Pieces of the engine (valve, valve seat ring,
  piston ring etc.)
• Pieces of exhaust manifold breaking off

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3. Foreign objects enter compressor or turbine

• Problem
• Customer claims that the locknut has come loose
  and destroyed the compressor wheel.
• Answer
• Right-hand thread ? possible, if the locknut has
  not been tightened and secured according to
  specifications.
• Left-hand thread ? not possible!The locknut will
  loosen itself if the shaft is jammed due to lack
  of oil because the compressor wheel wants to
  rotate.

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This damage could be caused by the locknut
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This damage is NOT caused by the locknut
Loose locknut ? Comp/wheel not fixed on the shaft
? When foreign object hits the blades, the wheel
gives way ? Not enough torque to destroy the
blades!
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Compressor wheel with foreign object damage
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Compressor wheel blades worn away
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Compressor wheel eroded by sand or dust
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Compressor housing damaged by dirty air
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Turbine wheel damaged by foreign object
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Comp/wheel damaged by a soft foreign object
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Turbine wheel damaged by foreign object
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3. Foreign objects enter compressor or turbine

• Preventive action
• Extreme caution during inspection and maintenance
  while pipes leading to the turbo are open.
• Carefully inspect and clean all air and gas
  piping before starting the engine.
• Use proper and high-quality air filters!

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4. Overspeeding and/or overheating

• Every turbocharger is designed for a maximum
  speed and a maximum temperature which it can
  bear, depending on the engine parameters air
  flow rate, boost pressure, exhaust gas
  temperature.
• Exceeding the speed limit continuously will cause
  mechanical failure. As the highest mechanical
  load occurs within the wheels, these are likely
  to fail first.
• In case of overheating without overspeeding, oil
  carbon build-up and cracked turbine housings can
  often be found.

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Burst comp/wheel due to overspeeding
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T/wheel burst due to overspeed overheating
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Turbine housing cracked due to overheating
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Cracks in the bypass channel due to overheating
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Engine Shut-off After 5 Min. Full Load
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4. Overspeeding and/or overheating

• Preventive measures
• Always use the correct turbo for the application
  (compare nameplates old new, check in our CD
  catalogue).
• Do not modify engine or turbocharger
  settings(e.g. wastegate).
• If the engine has been working hard, do not shut
  it down while it is hot
• ? let the engine idle for 30 sec to let it cool
  down.

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4. Overspeeding and/or overheating

• Specialist know-how
• Turbocharger overspeeding can often be
  detected.If the compressor wheel is still
  intact, measure bore diameter in 3 places d1, d2
  and d3. If overspeeding has occurred, d2 and d3
  will have expanded. At d1 no expansion occurs.
• The differences are a few micrometers only!

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5. Unprofessional turbo repairs

• Reduced lifetime can result from
• Wrong tolerances and clearances in bearing system
• Wrong material of critical parts
• Parts being re-used which shouldnt
• Rotor unbalance
• Incorrectly tightened and secured nuts bolts
  coming loose
• Wastegate not correctly calibrated, resulting in
  incorrect turbocharger performance and possibly
  overspeeding.

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5. Unprofessional turbo repairs

• Unbalance of used rotating parts can result from
• Small blade defects/deformations
• Gravity-drop of turbine wheel after hot
  shutdown
• Deposit build-up on wheel(s)
• Rotor unbalance reduces turbo life because
• Bearing suffers one-sided wear
• With heavy unbalance, oil film is continuosly
  interrupted
• Eventual failure due to increased bearing play
• ? Unbalance will often lead to bothering piping
  noises!

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Journal bearing worn on one side by unbalance
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Shaft and journal bearing worn on one side
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5. Unprofessional turbo repairs

• Preventive action
• Balance check and if necessary correction of
  rotating components, high-speed balancing of core
  assembly for small turbos (requires specialised
  balancing equipment).

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X. Oil leakage

• A turbocharger does not have 100-seals. They
  only work while
• the shaft rotates
• the piston rings have tension in their seats
• the pressure in the end housings is equal or
  higher than the pressure in the bearing housing.
• This will not be true in the following cases-
  Oil drain from turbo is obstructed- Crankcase
  ventilation does not work properly- Oil level in
  sump is too high- Air filter or induction pipes
  are obstructed.

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X. Oil leakage

• If a turbo leaks oil, check the aforementioned
  reasons first.
• When these can be excluded, the fault is usually
  a worn out piston ring groove.
• Reasons that the piston ring groove is worn
  out- Bearing play increased due to dirty oil or
  lack of oil- Piston ring not fitted correctly
  during assembly ? having contact with
  shaftwheel / flinger sleeve ? or piston ring
  broken during assembly- Piston ring not
  perfectly flat, i.e. the ends have an offset
  (this is a product defect).

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Turbine heat shield with oil carbon deposits
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X. Oil leakage

• Preventive measures
• Check all possible causes before identifying the
  turbocharger as the source of the problem.
• If you think it is the turbos fault,
• but after replacing the turbo the problem is
  still there,
• there are two possibilities
• The turbo manufacturer has a BIG quality
  problem,
• Or the trouble is caused by something else.

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When fitting the new turbo . . .

• Carefully check and clean all piping to from
  the turbo
• Change engine oil, oil filter and air filter
• Fill the bearing housing with clean engine oil
• Use new, correct fitting gaskets onlyDON'T USE
  LIQUID SEALANT!It blocks oil passages inside the
  bearing housing
• After the first start let the engine idle for 30
  sec until the oil print buoyed on in the whole
  system

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Instruction leaflet coming with each turbo
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BorgWarner Turbo Systems Warranty Terms

• These terms concern BorgWarners direct customers
  only, i.e. OEMs or Distributors. Customers of our
  customers cannot claim warranty against
  BorgWarner.
• Products which prove defective within 12 months
  after installation or at the latest within 18
  months after dispatch will be replaced or the
  defect removed free-of-charge.
• The defect must be caused by circumstances prior
  to dispatch.
• The buyer must file a written complaint
  immediately wherein the defect is described.

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Failures NOT covered by BorgWarner warranty

• Normal wear
• Improper interventions or repair work by third
  parties
• Unsuitable or improper use
• Faulty operation, assembly or commissioning
• Faulty or neglectful treatment
• Incorrect maintenance
• Use of unsuitable tooling/replacement materials
• Harmful environmental conditions
• Chemical, electrochemical or electrical
  influences
• Changes made on the product without our approval