These bearings provide, through their greater length, a stabilising influence on shaft alignment and longitudinal vibration. They tend to be adopted in the larger turbocharger, the thrust being taken by a face machined to provide the requisite oil wedges, similar to those formed in the classic tilting pad thrust block. In fact some models do adopt tilting pad thrust blocks. The clearance in these must be set so as not to interfere with the rotor to casing clearance mentioned above. Sleeve type bearings are usually supplied with oil from an external feed.\r\n
This supply, externally cooled, has a reverse supply (usually from some form of header tank) that protects the bearings during the run down period. That is, the engine may be stopped, perhaps because of failure of the main lubricating oil supply, but the turbocharger would run on for some time, and the bearings would still need lubricating during that time. Ball/roller races, because of their negligible clearance, require a cleaner oil and so are usually supplied from a supply integral to the turbocharger casing. In this respect they are self-sufficient, and will self-lubricate under the run-down conditions mentioned above (shaft driven gear type pumps or discs and scrapers).