The journal bearings used in internal combustion engines include the main crankshaft bearings, connecting rod bearings, and accessory bearings and seals. They are cylindrical with finish as smooth as possible.

In normal conditions, they operate in the hydrodynamic friction regime. However, during startup and shutdown, due to the low speed, is common to observe elastic-hydrodinamic or boundary-layer lubrication occurring. In these last cases, for example, the shaft maintains metal to metal contact with the bearing.

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