SLEEVE (JOURNAL) BEARINGS IN MODERN TURBOCHARGERS

• Sleeve (journal/ plain) bearings have a higher load-carrying capacity and can operate at the very high speeds of turbocharger rotors (tens of thousands of rpm) with a stable oil film.
• They are more tolerant of high speed and high temperature, and are less prone to fatigue failure than rolling bearings at these speeds.
• They provide better damping of vibration (the oil film absorbs vibration), reducing rotor vibration and noise.
• They are simpler, more robust, and have a longer life under continuous high-speed operation.
• They are less sensitive to shock/ impact loads than rolling bearings.
• They are easier to lubricate (from the engine's oil system) and do not require the special grease/ seals of rolling bearings.
• Rolling bearings at very high speed suffer from centrifugal loading on the rolling elements, fatigue, and limited life; sleeve bearings avoid these.

• The turbocharger bearings (journal and thrust) are lubricated by oil from the engine's main lubricating oil system (or a dedicated supply). Oil is fed to the bearing housing through a supply line, enters the bearing, forms a hydrodynamic oil film between the journal and the bearing, and drains back to the sump/ oil system.
• The oil is filtered (a filter/ strainer in the supply) and the oil pressure/ flow is maintained. The oil also cools the bearing. A thrust bearing (to locate the rotor axially) is also lubricated.
• The oil drains from the bearing housing back to the engine sump/ oil tank. The oil temperature and pressure are monitored.

1. Stop the engine and the turbocharger; isolate the oil supply and allow the T/C to cool.
2. Remove the turbocharger covers/ end plates to access the bearing housings.
3. Remove the rotor (the shaft with the turbine and compressor wheels) carefully, supporting it, and land it on a clean stand.
4. Remove the old bearings (journal and thrust) from the bearing housings, noting their position/ orientation.
5. Clean and inspect the bearing housings, the shaft journals and the thrust faces for wear, scoring and damage.
6. Fit the new bearings (journal and thrust) in the correct position/ orientation, ensuring they are correctly seated.
7. Refit the rotor, checking the axial (end) float and the radial clearances to the maker's specification.
8. Refit the covers/ end plates with new gaskets/ O-rings.
9. Reconnect the oil supply and prime the bearings with oil (before running).
10. Run the turbocharger up slowly and check the oil pressure, temperature, vibration and the rotor free rotation; confirm normal operation.