When overhauling the engine it is wise to retain the old main and connecting rod bearings since they can give very useful information on the engine. Contamination, wear and tear from usage, over-revving the engine which puts a lot of strain and load on the bearings, and corrosion which can be air born are some of the causes of failure that will need rectification before the next assembly process. When inspecting bearings, extract them from their areas of installation and place them adjacent to a clean surface so as be match up any problems with the crankshaft journal. Contaminants may be carried into the engine during assembly, may leak through, or result from machining operations and get lodged into the bearing material and cause scoring or gouging. To avoid this; it is recommended that all the parts are wash thoroughly and that the oil and filters are changed frequently. It can be due to high temperatures, overloading, leakage of oil or obstruction of oil ways, which can cause lot of impairment, including heating up of bearing backing. Fortunately, we also have influence over some driving habits that affect bearing endurance; for example, low speed with a full throttle will cause fatigue failure, short running will result in corrosion from inadequate heat. Any improper installation takes its toll and after a while can cause such things as oil starvation or high spots that will lead to the failure. If original bearings are worn or if oil clearances are incorrect new bearings will have to be chosen even more carefully, particularly in the case where the crank shaft has been reconditioned and the bearings are of an undersize. For standard size main bearings, use the colour code of the original part and if illegible the crankshaft journal diameter and main bearing bore grade letters. Standard and 0.25mm less connection rod bearings are available and these are marked on them. Finally, it is the oil clearance that becomes the deciding criterion for selecting new bearings, though it may be necessary to seek the help of a dealer if some doubt is felt.