When overhauling an engine, it is standard practice to replace the main and connecting rod bearings with new ones, but it is useful to retain the old bearings, as these will reveal much about the condition of the engine. Some of the causes of bearing failure include inadequate lubrication, the presence of dirt or foreign particles, overloading the engine and corrosion, all of which have to be eliminated before re-fixing the engine for the same not to recur again. While inspecting the bearings they should be taken out of the engine parts and arranged in the same position on a flat surface so that in case of any flaw it may be matched with the crank shaft journal. Particles from other sources can be introduced in the engine during assembly time or through the filters, the PCV system, or can be residual chips or abrasives from a previous machining or reconditioning. The former may get lodged within the bearing material, while the latter score or gouge the bearing surface. To avoid such failures the interior as well as the exterior part of the car should be well cleaned and the oil and filter should be changed. Crushing of bearing due to lack of lubrication is normally due to heat stress, overloading, oil leaking or blocked oil ways and results in the bearing material being wiped fully off its backing. Some driving practices also affect bearing life in a vehicle; for example very low speed with a full throttle puts a lot of load which forces out the oil in the bearings while short journeys may cause corrosion owing to low heat generation. Also, incorrect bearing fitment leads to lasting oil starvation, or high spots that lead to failure sometimes.