When overhauling an engine, a smart move is to change the main and connecting rod bearings, keep the old ones so as to study them, these offer clues to the overall performance of the engine. This mostly originates from lack of lubrication, contaminants such as dirt or any foreign particle, overloading of the engine, or corrosion, and such issues must be fixed prior to the next assembly. When inspecting bearings, pull them out of their corresponding locations and arrange them neatly for possible pairing of the defects with the crankshaft journal. Foreign particles could be forced into the engine during the assembling process, getting through the filters, or through the machining of Bear inGs; and small foreign bodies tend to get lodged into the bearing material, larger bodies, on the other hand, result in scoring. Precautions include frequent washing of all the components and regular changing of oil and filter. Thus, the cases of failure in lubrication may be caused by issues like overheating, overloading, oil leaks or blockage of the oil circulation channels which results to severe damages. Other driving conditions, like full throttle at low speeds or short distances, also affects bearing life as well by wearing off the oil film and also leading to corrosion. A proper assembly is not achieved, for example tight fitting bearings or trapped dirt, results in the cutting off of oil supply and thus fails. When it comes to bearings, in case of clearance or supply of wrong bearings or replacement of original bearings, refer the chart to select the standard bearings. If the crankshaft has been reground, new undersize bearings will be required and the automotive machine shop can help in choosing the correct one. The oil clearance obtained ought to be used to determine the right size bearings, by referring to the record of Plastigage. In factory-assembled engines, bearings utilize different coloured insert and the journal size codes are normally inscribed on the crankshaft. If achieving select fit is required it is possible to have two inserts of different sizes one being larger than the other; however, one must ensure that these sizes do not differ by more than 0.001 inch. Generally, odd-size inserts must be complementary, with all top inserts the same size and all bottom ones the same size.
Posted by ToyotaPartsDeal Specialist 
