What is an Engine Bearing, and what does it do?

A bearing is a device used to reduce friction between moving parts of machine elements to provide movement in the desired way with minimum power losses. The development of bearings is one of the most revolutionary steps in the development of human-made machines. Leonardo da Vinci described the first concept of a bearing. The main engine bearings' function is to support the crankshaft and allow rotation during the engine operation. Main bearings are mounted in the crankcase.

The rotating components of internal combustion engines are equipped with sleeve type sliding bearings. The reciprocating engines are characterized by the cycling loading of their parts, including bearings. Such character of the loads is a result of alternating pressure of combustion gases in the cylinders. Rolling bearings, in which a load is transmitted by rolls (balls) to a relatively small area of the ring surface, can not withstand under the loading conditions of internal combustion engines. Only sliding bearings providing a distribution of the applied load over a relatively wide area may work in internal combustion engines.

Main Functions of Bearings

  • Reducing friction
  • Supporting parts of the machine or machine elements
  • Bearing radial or thrust laods

Main crankshaft bearings support crankshaft providing its rotation under inertia forces generated by the parts of the shaft and oscillating forces transmitted by the connecting rods. Main bearings are mounted in the crankcase. The main bearing consists of two parts: upper and lower. The upper part of the main bearing commonly has an oil groove on the inner surface. The main bearing has a hole for passing oil to the feed holes in the crankshaft. Some of the main bearings may have thrust bearing elements supporting axial loads and preventing movements along the crankshaft axis. The main bearings of such type are called flange main bearings.

The main bearings are located in the engine block where the crankshaft is situated. One shell is located in the engine block and the other in the crank cap. Main bearings may have specific characteristics such as oil holes, locating tags, and oil grooves.

Connecting rod bearings provide a rotating motion of the crankpin within the connecting rod, which transmits cycling loads applied to the piston. Connecting rod bearings are mounted in the Big end of the connecting rod.

Small end bushes provide the piston's relative motion relative to the connecting rod joined to the piston by the piston pin (gudgeon pin). End bushes are mounted in the Small end of the connecting rod. Small end bushes are cycling loaded by the piston pushed by the alternating pressure of the combustion gases.

These bearing are located at the smaller end of the connecting rod. This is where the gudgeon pin of the piston is located. We can source these bearings if your conrod requires them. Often these bearing come with the conrod. Small end bushes either come at a specific size or need to be lined bored to achieve the correct fit.

Camshaft bearings support the camshaft and provide its rotation. The bearings sit between the cylinder head casting and the camshaft caps, which house the camshaft. These bearings may have oil holes for specific engines to help keep the camshaft lubricated.

Thrust washers are either separate from the main bearing or integrated into one or two of the main shells. The thrust washer is designed to govern the lateral movement of the crankshaft. This is called the "end float." Oversize thrust washers are available for some engines so the end float can be re-calculated if there is excessive wear. 

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