To say the least, when reconditioning an engine, it is required to use new main and connecting rod bearings although the old ones should be retained for serious examination as these will give a clue on the engine. Causes of bearing failure include lack of lubrication, contaminants such as dirt or particles, overworking the engine, and corrosion and such problems must not be overlooked while disassembling but fixed to avoid being repeated. When inspecting the bearings, they should be pulled out of the engine block and spread on a flat surface in their original position in order that problems be matched with the crankshaft journal. Foreign particles can be got into the engine during assembly, in passing through the filter or through the PCV system or from tramp metals and abrasive from the machining or after reconditioning. Contaminants can be incorporated into the bearing metal matrix, while undergone material resulting in scoring or gouging can result from the large size particles. Thus, to avoid such failures, cleaning of all parts and routine engine oil and filter should be done. Failure of greasing can be consequent of high temperatures, overloading, leaking or choked oil channels which may cause serious damage such as extrusion of bearing surface material right from its metal jacket. Other dynamic considerations also greatly influence bearing life; when a vehicle is raced at low speeds, high loads are obtainable that can push out the oil film whereas short distance travel can cause corrosion because of inadequate heat build up. Also, wrong orientation of bearings can lead to oil starvation because they may be pressed in tightly or because of dirt, debris and gunk trapped behind inserts leading to high spot fatigue failure.