Turbochargers

A turbocharger is a forced induction system that uses the energy of exhaust gas, which would otherwise be lost, to spin a turbine. That turbine is connected by a shaft to a compressor that compresses the intake air. With more air in the cylinder, more fuel can be burned on each cycle and the engine produces more power without increasing in size.

Almost all modern diesel engines in cars, trucks and machinery have a turbo, because diesel engines run with excess air and benefit especially from forced induction.

The rotating assembly includes the turbine wheel, the shaft and the compressor wheel, and it spins at tens of thousands of revolutions per minute supported by a film of engine oil. Around it are the turbine and compressor housings and the system that regulates boost pressure.

That regulation can be done with a wastegate, which bypasses part of the exhaust gas to limit pressure, or with variable geometry, where movable vanes change the flow. Actuators can be pneumatic or electronic and are controlled by the ECU.

The turbo is very sensitive to lubrication. Lack of oil, degraded or contaminated oil, a clogged filter or a blocked drain line are the most frequent causes of shaft and bearing wear. Particles or foreign objects entering through the intake or exhaust also damage the vanes.

In variable geometry turbos, carbon can leave the movable vanes stuck, causing loss of power or excess pressure. That is why it is important to find and fix the original cause before fitting a repaired or new turbo.

Because the rotating assembly turns at such high speeds, even a minimal imbalance creates vibrations that destroy the bearings in a short time. After a turbo is repaired, the assembly is balanced at a speed close to working speed and mass differences are corrected.

It is a step that cannot be seen from outside, but it determines whether the repair holds: a turbo without correct balance may sound fine at first and fail soon after.