When the engine is being overhauled, although new main and connecting rod bearings are supposed to be fitted, the old bearings can be kept so that they can give information on how the engine was. Failure may occur due to ineffective lubrication, dirt or foreign objects, overloading of an engine, and corrosion, among others, which need to be taken care of and never re-occur in time of reassembly. When checking bearings, take them off their respective locations and place them in a clean place so as to match any problem with the crankshaft journal. The foreign particles may enter the engine during assembly, through filters, or machining operation and may be embedded in the material used to make the bearing and any larger particle can score. To avoid such failures, it is necessary to clean all parts of the parts properly and change the oil and filters regularly. Deficiency in lubrication may be attributed to too much heat, overloading, spillage of oil or blocked openings and extreme damage can occur. Driving patterns also influence bearing life; e.g. loading up the engine or taking short journeys may lead to oil shortage and rusting. Poor installation may also cause malfunctioning caused by inadequate space or stagnant debris. In case of worn original bearings or erroneous oil clearances, correct choice of new bearings is very important, particularly when the crankshaft has been regrounded, and then undersized bearings should be fitted. In case of standard size bearings use them as they are and in case of need, get a professional machine shop of engines to vary them. Finally, the most important aspect to be used in choosing the correct bearing sizes is the oil clearance, and a dealer or service department should be used to aid in making sure about uncertainties.