oil related failure

In the event of an lubrication failure to the turbocharger bearing system and shaft, I often get asked why the main bearing of the engine survive a lubrication failure.
There are numerous reasons for this.

  • The turbo is generally the furthest away from the oil pump and is the first to suffer when oil pressure drops or fails completely
  • The crank turns at an average of 5000 rpm in general operation conditions and the turbo at 160,000 rpm.
  • The main and big end bearings are made from a much more complex material and operating design and have completely different load functions to contend with. Where main bearing are designed to absorbs impurities, the turbo bearings are not.
  • Turbo bearings are more susceptible to two types of wear. Abrasive wear. Abrasive wear is the characteristic for a third material to get in between the bearing and shaft. Carbon deposits and impurities from machining and cam grinding.
  • The heat and speed generated inside the turbo shaft system makes it vulnerable to adhesive wear. This is when the two surfaces begin to fuse together or bond and pieces are torn off of one of the surfaces and bonded to the other
  • The oil supply pipe from the block to the turbo is generally pretty close to the exhaust and heat source.In engine shut down periods this oil can boil in the pipe and form deposits which are then forced through the bearings. These deposits cannot be removed by general cleaning.

Its a known fact that any small impurities like carbon get embedded into the main bearing shell and do not cause wear. Bearing material in the crankshaft bearing is designed to do this function to prolong bearing life in an engine. adesiveWearTurbocharger bearing are generally made from a brass alloy as a bush and have very small clearances and impurities will cause wear to both shaft and bearing in a very short amount of time. The limited friction properties of brass materials cause the galling pattern of wear, caused by insufficient lubrication.

Adhesion wear is a result of micro-junctions caused by welding between the opposing rough surfaces rubbing on the counter-bodies. The load applied to the contacting surfaces is so high that they deform and adhere to each other forming micro-joints. The motion of the rubbing counter bodies result in rupture of the micro-joints where some of the material is transferred by its counter-body. This effect is called scuffing or galling. Eventually this will cause the seizure of one of the bodies by the counter-body. This is a common sight found when stripping a turbocharger and inspecting the bearing and shaft journals. The blue to purple discoloring is caused by excessive heat and the brown colouring on the shaft is the brass adhesion onto the shaft.

With this in mind it is imperative that the engine builder and, or turbo fitter has made sure that the inside of the motor and oil galleries have been cleaned properly and using the correct cleaning material. Unfortunately paraffin is one of the worst cleaning materials when used on its own. After cleaning it is essential that it gets washed again with HOT WATER and soap at high pressure. Oil supply lines need to be replaced as deposits CANNOT be removed by cleaning.

Most “warranty” failures are cased by this.

 

Turbo Failures

Reasons for Turbocharger Failure

There are three major reasons for turbocharger failure:

  • faulty lubrication,
  • excessive condensation,
  • and a lack of regularly scheduled maintenance.

Lubrication Failure –

Proper cooling and lubrication are vital to turbocharger operation.
Turbochargers are driven by hot exhaust gases
exiting the combustion chamber and, therefore,
are subject to extreme temperatures. In a Burst
& Containment Document authored by Honeywell [2], their Garrett Engineering group
provides an operating description of its smallestsw object damage
turbo product. The article states that the
turbocharger’s impellers operate up to 200,000
rpm and the exhaust gas temperature can reach a
max of 1800°F, causing the turbine housing to
glow red under certain driving conditions.
Circulating engine oil through the turbocharger
to remove heat and provide lubrication to
internal components ensures functional
operation. A lack of lubrication from degraded
engine oil or insufficient delivery from an
obstructed oil line can cause increased friction
and temperatures. In extreme cases of poor
lubrication and high operating temperatures,
moving components can become seized, locking
up the turbocharger and disabling operation of
the vehicle. Excessive Condensation –

Many high performance turbochargers are known for their
variable geometry turbines (VGT or VNT).
These units have controlled vanes, which help
increase or decrease impeller speed within the
turbine’s housing. Seized or sticking vanes
cause performance failures on this type of turbo.
Rust formations on the vanes, created by
excessive condensation build-up when a vehicle
is idle for extended periods of time, is the cause
of failure. Condensation can enter the tail pipe
or an exhaust manifold gasket leak. Typically,
this occurs from irregular or sporadic driving.
Regular on-the-road vehicle use will help burn
condensation and prevent rusting.

Lack of Maintenance –

Turbocharged engines require thorough care with stable, regularly
scheduled maintenance cycles for lubrication
systems, air filters, seals and gaskets. As
previously noted, catastrophic failure can occur
when engine oil changes become infrequent and
fail to meet recommended scheduling intervals.
Air filter maintenance is vital to eliminate
foreign object damage (FOD) to the charged air
impeller. Research shows that under normal
driving conditions, most medium-duty diesel
vehicles have an average operation life of 10
years or 100,000 kilometers on their exhaust systems.
At 100,000 kilometers, inspecting and cleaning the
intercooler system and removing any cause of
FOD is highly recommended. After excessive
miles, turbochargers comp object damagesometimes experience
pressure loss caused by worn seals (leakage)
and/or worn impeller (leakage). Seals will easily
damage under extensive pressure cycles,
especially sealing rings for rotating parts.
Foreign object damage to impeller, as well as
chipped or bent vanes on impellers, will reduce
required energy efficiency to increase
combustion pressure (power).