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Engine Bearing Functions
This section examines engine bearings. No engine can run without bearings. Bearings used engines to support and protect rotating paths and allow them to turn freely. The connecting rod must be able to spin freely on the crankshaft. The crankshaft shaft must be able to spin freely in the engine block.
Connecting rod bearings and the crankshaft main bearings are called split sleeves types, which mean they are in two halves called inserts, slippers, or shells. These position inserts have a steel back with a very thin layer of bearing material bonded to it. The bearing material is an alloy that can include metals such as tin, lead, aluminum, and copper.
Bearing is designed for light duty maybe made of white metal. It is an alloy of tin and lead with small amounts of copper and antimony. Alloys of tin and aluminum improved the load carrying capacity for intermediate applications. Copper and lead alloys give even more improvements. They use an applications such as diesel engines and high performance vehicles.
Bearings need a difficult mix of properties. They must be hard enough to resist where but soft enough not to damage the shaft. The soft bearing surface also allows any hard abrasive particles to become embedded in the surface. They can become so deeply embedded. They are prevented from touching the rotating shaft by the film of oil. It is the mix of metals, tin, lead, copper, and others into an alloy that makes this combination of hardness and softness.
In a main bearing, the upper half of the bearing fits into a machine section of a crankcase web. The lower half is carried in the bearing cap which vaults onto the crankcase web. In a connecting rod bearing its upper half is carried in the big end of the connecting rod. The lower half is in the connecting rod cap. One main bearing has thrust phases which accept the end movement of the crankshaft. This can be in the form of plungers for the post of the bearing. Alternatively a separate thrust washer can be fitted into a machined recess in each side of the bearing cap.
Sometimes amazing recess for each side is machined into the cylinder block and making halves fitted to both. Under normal running conditions, spinning shafts right on the microscopic wedge of oil, oil flows through a long gallery in the cylinder block. Each main bearing has its own oil supply passageway from this gallery. Passageways drilled in the crankshaft carry oil form the main bearing channels through rod channels. Oil flow maintains the oil wedge between the shaft and bearing and carries away particles that could cause wear.
Engine manufacturers specify the clearance required between the bearing material and the crankshaft. This clearance gives the best combination of oil pressure and flow. As clearance increases with wear, oil flow increases causing oil pressure to drop. Then the shaft may rub against the bearing surface and wear even faster.
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