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Main bearing
 
 
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In a piston engine, the main bearings are the bearings
Bearing (mechanical)

A bearing is a device to allow constrained relative motion between two parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle....
 on which the crankshaft
Crankshaft

The crankshaft, sometimes casually abbreviated to crank , is the part of an engine which translates reciprocation linear piston motion into rotation....
 rotates, usually plain or journal bearing
Journal bearing

A journal bearing is a simple Bearing_ in which a Axle, or "journal", or crankshaft rotates in the bearing with a layer of oil or Grease separating the two parts through Fluid dynamics....
s.

All engines have a minimum of two main bearings, one at each end of the crankshaft, and they may have as many as one more than the number of crank pin
Crank pin

In a reciprocating engine, the crankpins, also known as crank journals are the Bearing journal bearing of the big end bearings, at the ends of the connecting rods opposite to the pistons....
s. The number of main bearings is a compromise between the extra size, cost and stability of a larger number of bearings and the compactness and light weight of a smaller number.






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In a piston engine, the main bearings are the bearings
Bearing (mechanical)

A bearing is a device to allow constrained relative motion between two parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle....
 on which the crankshaft
Crankshaft

The crankshaft, sometimes casually abbreviated to crank , is the part of an engine which translates reciprocation linear piston motion into rotation....
 rotates, usually plain or journal bearing
Journal bearing

A journal bearing is a simple Bearing_ in which a Axle, or "journal", or crankshaft rotates in the bearing with a layer of oil or Grease separating the two parts through Fluid dynamics....
s.

All engines have a minimum of two main bearings, one at each end of the crankshaft, and they may have as many as one more than the number of crank pin
Crank pin

In a reciprocating engine, the crankpins, also known as crank journals are the Bearing journal bearing of the big end bearings, at the ends of the connecting rods opposite to the pistons....
s. The number of main bearings is a compromise between the extra size, cost and stability of a larger number of bearings and the compactness and light weight of a smaller number. Both have advantages in terms of performance, as a shorter and more stable crankshaft
Crank

Crank may refer to:...
 will produce better engine balance
Engine balance

Engine balance is the design, construction and tuning of an engine to run smoothly. Engine balance reduces vibration and other Stress , and may improve the performance, efficiency, cost of ownership and reliability of the engine, as well as reducing the stress on other machinery and people near the engine....
.

Examples:

  • All single and V-twin cylinder engines have at least two main bearings, one at each end.


  • Parallel (inline) twin engines as used in motorcycles may have two, three, or four main bearings. Broadly speaking, older British twins had two main bearings. Japanese twins typically have four.


  • The oil groove is also referred to as the caspian groove. "Caspian" referring to a Sir Caspian Cruz, an early 1920s automotive engineer credited with improving lubricating properties for small automotive engines prompted by the short lifespan of inferior bearing materials.


  • Most four cylinder petrol and some inline six
    Straight-6

    The straight-6 or inline-6 engine is a six cylinder internal combustion engine with all six cylinder mounted in a straight line along the crankcase....
     engines have three main bearings, the third in the middle. However, four cylinder inline Diesel engines usually have five main bearings due to the heavier loads imposed on the crankshaft.


  • Almost all current production inline six cylinder engines have seven main bearings. Older inline sixes often had either three or four main bearings.


  • All modern V8 engines have five main bearings, with one crank pin between each pair of adjacent main bearings. Old designs, such as the Ford flathead V-8
    Ford Flathead engine

    The Flathead was the first independently designed and built V8 engine produced by the Ford Motor Company for mass production and ranks as one of the company's most important developments....
    , produced from 1932 through 1953, often had three mains.


  • Most straight-5
    Straight-5

    The straight-5 or inline-5 is an internal combustion engine with five Cylinder aligned in one row, sharing a single engine block and crankcase....
     engines have six main bearings, to help counter the essential imbalance of this design.


When describing a crankshaft design, the number of main bearings is generally quoted, as the number of crank pins is determined by the engine configuration
Engine configuration

Engine configuration is an engineering term for the layout of the major components of an internal combustion engine. These components include cylinder s, pistons, crankshaft and camshaft....
. For example, a crankshaft for an inline six engine will be described as three bearing or four bearing depending on its number of main bearings; The crank pins are not counted in this description. Similarly, when speaking of a crankshaft, the journals are the main bearing journals only. The crank pins are not normally called journals although they form the centre shafts of the big end bearings and are therefore journals in the more general sense.