Q: What is the importance of retaining old bearings during the engine inspection process on Nissan Xterra?
A: The old bearings must be kept during engine inspection although these will be replaced with new ones as part of the overhaul because they can give vital information on the condition of the engine and potential problems. For example, bearing failure may be due to factors such as inadequate lubrication, dust or foreign matter, overloading of the engine and corrosion. Bearings are removed from their positions of assembly like those in the engine block, main bearing caps, connecting rods and rod caps then arranged systematically so as to relate any bearing faults with their respective journal in the Crankshaft. Foreign particles such as dust and metal chips can also enter into an engine through various ways including assembly, filtration or even PCV mechanisms causing more harm on bearings and scratching. This can be solved by adopting proper cleaning techniques that include thorough part cleaning and keeping clean during assembly, regular oil changes together with frequent filter replacements. Bearing failure can also occur when lubrication breaks down which is caused by things like excessive heat, overloading, oil leaks, blocked oil passages resulting in wiped or extruded bearing material on a worn out camshaft lobe. For instance driving habits like high load application at low speed operation of high gears or short trip driving exposing bearings to flexing corrosion leading to shorter life span. When building an engine it is essential to use correct bearing installation techniques hence tight fitting or incorrectly placed bearings being some symptoms of starvation for oil and hence bearing failure most often results from incorrect installation of bearings onto a crankshaft during assembly process. New bearings have to be procured if original bearings become worn out damaged or have incorrect oil clearances. In most cases new replacement bearings are used during a complete car engine rebuild especially where there was some considerable milage covered by this motor. If the crankshaft has been re-ground then undersize bearings must be used corresponding to the amount of material removed from it . Generally ground in 0.010 inch increments that vary depending on the specifications of the automotive machine shop reconditioning the crankshaft. Plastigage measurements are helpful for determining bearing sizes regardless of how this is done and when there are doubts about size selection, it is necessary to contact the machine shop or dealer parts/service department.