Though the main & connecting rod bearings must be substituted for the new one while doing the overhaul of the engine, it is desirable that use of old bearings must be kept & studied closely because they will give a quite insight & idea about the status of the engine. There are several causes of bearing failure they include; Lack of lubrication, the presence of a foreign particle such as dirt or any other, overloading the engine, corrosion. Regardless of the cause, any such condition will have to be rectified before assembly in order to avoid a repetition of the same. When inspecting bearings, pull out the bearings together with the caps from the engine block and remove the main bearings caps, connecting rods and rod caps; arrange the bearings in the same general positions as they were in the engine to match the bearings defects to the specific crankshaft journal. Contaminants may include dirt and foreign particles that can find their way into the engine at the time of assembly or through some filters, PCV and so on, metal chips, abrasives and many others that may be left in some reconditioned parts. Such foreign objects tend to become lodged in the softer bearing material while large particles can actually scratch or cut into the bearing and journal. Prevention of this involves regular cleaning of all parts of the car and changing of oil and filters frequently. Obviously the major reasons for lack of lubrication are as follows: Over heating, overloading, oil leakage and blocked oil passages all of which contribute to bearing destruction. Motor driving habits also influence bearing life; low speed touring often selects excessive gear high loads which may extrude oil film causing fatigue failure whereas too many short trip often cause corrosion due to lack of engine heat. Failure can also be caused by improper bearing installation, for example, it is possible to have SPE bearings fitted too tightly, which results in oil deprivation or having dirt trapped in the bearing due to which high spots on the bearing are created.