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Fitting the correct engine bearings and premature malfunction can arise from a host of reasons. When building an engine, fitting the crankshaft bearings is always touchy. Crankshaft bearings and their respecticve journals are probably the most important rotating parts of any engine and there are many reasons that can be attributed to premature ‘crank to bearing’ failure. Stripping the engine will always show evidence to which part is the culprit.
The crankshaft bearings have a dual function of reducing friction between the rotating journals of the engines crankshaft big end and main journals and the stationary parts, which are the connecting rods and the main caps of the engine block. The main caps are responsible for supporting the crankshaft while the big ends are the crank throws which are responsible for pushing the pistons up and down from TDC to BDC.
Explosions caused inside the combustion chambers require the bearing material to be extremely strong and therefore a durable metal surface is required. Reducing friction is accomplished by allowing dissimilar metals to slide against each other with less friction and wear and tear than similar materials would do.
Any material used for a process such as this would give the engine bearing certain friction reducing properties and is enhanced by forcing a constant flow of lubricant between the bearing and crank journal, thereby enhancing the reduction in friction between the moving and stationary surfaces. Another one of the bearing’s main functions is to establish and maintain a film of oil and therefore bearings are manufactured from porous materials.
All these functions are harmoniously engineered to work within the smallest acceptable tolerances, however, when a crankshaft or one of its bearings fail the results can be catastrophic. Most often crankshaft to bearing failure is most often associated with a faulty bearing, together with other underlying factors that require a closer inspection which often points to debris of some type or other.
Some bearing to crankshaft failures are caused by a combination of factors which must be rectified at all costs before repairs can commence. Firstly, ensure that your oil pump is supplying adequate oil flow, and then determining the most likely cause of failure would entail stripping the entire engine down and methodically clean each and every part, paying special attention to the crankcase and its relative components.
Whether you find dirt from grinding remnants in an oil gallery, the smallest dust debris can cause significant damage to bearing surfaces thereby dramatically shortening engine life. Other problem areas to check are malfunctioning oil pumps, improper bearing selection and fuel dilution, which is most often caused by blow-by or simply leaking injectors or carburetor.
Just as with the installation issues, incorrect machining can also result in bearing to crank failure. An out-of-round crankcase housing bore will cause the main bearing to distort and will be required to be line bored just as an out-of-round connecting rod would require resizing.
BMW POWER suppliers of all oversize BMW engine bearings www.bmwpower.co.za