Crankshaft

# Crankshaft

Overview
The crankshaft, sometimes casually abbreviated to crank
Crank (mechanism)
A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm...

, is the part of an engine
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...

which translates reciprocating
Reciprocation
Reciprocation may refer to:* Reciprocating motion, a type of oscillatory motion, as in the action of a reciprocating saw* Reciprocation in geometry, an operation with circles that involves transforming each point in plane into its polar line and each line in the plane into its pole...

linear
Linear
In mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...

piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

motion into rotation. To convert the reciprocating motion into rotation, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of the connecting rod
Connecting rod
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....

s from each cylinder attach.

It typically connects to a flywheel
Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

, to reduce the pulsation characteristic of the four-stroke cycle
Four-stroke cycle
A four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine's crankshaft, and one single thermodynamic cycle.There are two...

, and sometimes a torsional or vibrational damper at the opposite end, to reduce the torsion
Torsion (mechanics)
In solid mechanics, torsion is the twisting of an object due to an applied torque. In sections perpendicular to the torque axis, the resultant shear stress in this section is perpendicular to the radius....

vibrations often caused along the length of the crankshaft by the cylinders farthest from the output end acting on the torsional elasticity of the metal.

A Roman
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

iron crankshaft of yet unknown purpose dating to the 2nd century AD was excavated in Augusta Raurica
Augusta Raurica
Augusta Raurica is a Roman archaeological site and an open-air museum in Switzerland. Located on the south bank of the Rhine river about 20 km east of Basel near the villages of Augst and Kaiseraugst, it is the oldest known Roman colony on the Rhine....

, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

.
Discussion

Encyclopedia
The crankshaft, sometimes casually abbreviated to crank
Crank (mechanism)
A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm...

, is the part of an engine
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...

which translates reciprocating
Reciprocation
Reciprocation may refer to:* Reciprocating motion, a type of oscillatory motion, as in the action of a reciprocating saw* Reciprocation in geometry, an operation with circles that involves transforming each point in plane into its polar line and each line in the plane into its pole...

linear
Linear
In mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...

piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

motion into rotation. To convert the reciprocating motion into rotation, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of the connecting rod
Connecting rod
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....

s from each cylinder attach.

It typically connects to a flywheel
Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

, to reduce the pulsation characteristic of the four-stroke cycle
Four-stroke cycle
A four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine's crankshaft, and one single thermodynamic cycle.There are two...

, and sometimes a torsional or vibrational damper at the opposite end, to reduce the torsion
Torsion (mechanics)
In solid mechanics, torsion is the twisting of an object due to an applied torque. In sections perpendicular to the torque axis, the resultant shear stress in this section is perpendicular to the radius....

vibrations often caused along the length of the crankshaft by the cylinders farthest from the output end acting on the torsional elasticity of the metal.

#### Classical Antiquity

A Roman
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

iron crankshaft of yet unknown purpose dating to the 2nd century AD was excavated in Augusta Raurica
Augusta Raurica
Augusta Raurica is a Roman archaeological site and an open-air museum in Switzerland. Located on the south bank of the Rhine river about 20 km east of Basel near the villages of Augst and Kaiseraugst, it is the oldest known Roman colony on the Rhine....

, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

. The 82.5 cm long piece has fitted to one end a 15 cm long bronze handle, the other handle being lost.
The earliest evidence, anywhere in the world, for a crank and connecting rod
Connecting rod
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....

in a machine appears in the late Roman Hierapolis sawmill
Hierapolis sawmill
The Hierapolis sawmill was a Roman water-powered stone sawmill at Hierapolis, Asia Minor . Dating to the second half of the 3rd century AD, the sawmill is the earliest known machine to combine a crank with a connecting rod....

from the 3rd century AD and two Roman stone sawmill
Sawmill
A sawmill is a facility where logs are cut into boards.-Sawmill process:A sawmill's basic operation is much like those of hundreds of years ago; a log enters on one end and dimensional lumber exits on the other end....

s at Gerasa, Roman Syria, and Ephesus
Ephesus
Ephesus was an ancient Greek city, and later a major Roman city, on the west coast of Asia Minor, near present-day Selçuk, Izmir Province, Turkey. It was one of the twelve cities of the Ionian League during the Classical Greek era...

, Asia Minor
Asia Minor
Asia Minor is a geographical location at the westernmost protrusion of Asia, also called Anatolia, and corresponds to the western two thirds of the Asian part of Turkey...

(both 6th century AD). On the pediment
Pediment
A pediment is a classical architectural element consisting of the triangular section found above the horizontal structure , typically supported by columns. The gable end of the pediment is surrounded by the cornice moulding...

of the Hierapolis mill, a waterwheel fed by a mill race
Mill race
A mill race, raceway or mill lade is the current or channel of a stream, especially one for conducting water to or from a water wheel or other device for utilizing its energy...

is shown powering via a gear train
Gear train
A gear train is formed by mounting gears on a frame so that the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, this provides a smooth transmission of rotation from one gear to the next.The transmission of...

two frame saw
Frame saw
Frame saw sometimes refers to a woodworker's bow saw.A frame saw is a type of rip saw. It consists of a relatively narrow and flexible blade held under tension within a rectangular frame...

s which cut rectangular blocks by the way of some kind of connecting rods and, through mechanical necessity, cranks. The accompanying inscription is in Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

.

The crank and connecting rod mechanisms of the other two archaeologically attested sawmills worked without a gear train
Gear train
A gear train is formed by mounting gears on a frame so that the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, this provides a smooth transmission of rotation from one gear to the next.The transmission of...

. In ancient literature, we find a reference to the workings of water-powered marble
Marble
Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite.Geologists use the term "marble" to refer to metamorphosed limestone; however stonemasons use the term more broadly to encompass unmetamorphosed limestone.Marble is commonly used for...

saws close to Trier
Trier
Trier, historically called in English Treves is a city in Germany on the banks of the Moselle. It is the oldest city in Germany, founded in or before 16 BC....

, now Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

, by the late 4th century poet Ausonius
Ausonius
Decimius Magnus Ausonius was a Latin poet and rhetorician, born at Burdigala .-Biography:Decimius Magnus Ausonius was born in Bordeaux in ca. 310. His father was a noted physician of Greek ancestry and his mother was descended on both sides from long-established aristocratic Gallo-Roman families...

; about the same time, these mill types seem also to be indicated by the Christian saint Gregory of Nyssa
Gregory of Nyssa
St. Gregory of Nyssa was a Christian bishop and saint. He was a younger brother of Basil the Great and a good friend of Gregory of Nazianzus. His significance has long been recognized in the Eastern Orthodox, Oriental Orthodox, Eastern Catholic and Roman Catholic branches of Christianity...

from Anatolia
Anatolia
Anatolia is a geographic and historical term denoting the westernmost protrusion of Asia, comprising the majority of the Republic of Turkey...

, demonstrating a diversified use of water-power in many parts of the Roman Empire
Roman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

. The three finds push back the date of the invention of the crank and connecting rod back by a full millennium; for the first time, all essential components of the much later steam engine
Steam engine
A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...

were assembled by one technological culture:

#### Middle Ages

The Italian physician Guido da Vigevano
Guido da Vigevano
Guido da Vigevano was an Italian physician and inventor. He is notable for his sketchbook Texaurus regis Francie which depicts a number of technological items and ingenious devices, allowing modern scholarship an invaluable insight into the state of medieval technology...

Paddle boat may refer to:* Paddle steamer or paddleboat, a boat propelled by a paddle wheel* Pedalo, a boat propelled by pedalling with the feet* A boat which is paddled, such as a canoe or kayak...

and war carriages that were propelled by manually turned compound cranks and gear wheels (center of image). The Luttrell Psalter
Luttrell Psalter
The Luttrell Psalter is an illuminated manuscript written and illustrated circa 1320 – 1340 by anonymous scribes and artists...

, dating to around 1340, describes a grindstone which was rotated by two cranks, one at each end of its axle; the geared hand-mill, operated either with one or two cranks, appeared later in the 15th century;

#### Renaissance

The first depictions of the compound crank in the carpenter's brace
Brace (tool)
A brace or brace and bit is a hand tool used to drill holes, usually in wood. Pressure is applied to the top and the tool is rotated with a U-shaped grip....

appear between 1420 and 1430 in various northern European artwork. The rapid adoption of the compound crank can be traced in the works of the Anonymous of the Hussite Wars, an unknown German engineer writing on the state of the military technology of his day: first, the connecting-rod, applied to cranks, reappeared, second, double compound cranks also began to be equipped with connecting-rods and third, the flywheel was employed for these cranks to get them over the 'dead-spot'.

In Renaissance Italy, the earliest evidence of a compound crank and connecting-rod is found in the sketch books of Taccola
Taccola
Mariano di Jacopo detto il Taccola , called Taccola , was an Italian administrator, artist and engineer of the early Renaissance. Taccola is known for his technological treatises De ingeneis and De machinis, which feature annotated drawings of a wide array of innovative machines and devices...

, but the device is still mechanically misunderstood. A sound grasp of the crank motion involved demonstrates a little later Pisanello
Pisanello
Pisanello , known professionally as Antonio di Puccio Pisano or Antonio di Puccio da Cereto, also erroneously called Vittore Pisano by Giorgio Vasari, was one of the most distinguished painters of the early Italian Renaissance and Quattrocento...

who painted a piston-pump driven by a water-wheel and operated by two simple cranks and two connecting-rods.
One of the drawings of the Anonymous of the Hussite Wars shows a boat with a pair of paddle-wheels at each end turned by men operating compound cranks (see above). The concept was much improved by the Italian Roberto Valturio
Roberto Valturio
Roberto Valturio was an Italian engineer and writer born in Rimini. He was the author of the military treatise De Re militari .-References:...

in 1463, who devised a boat with five sets, where the parallel cranks are all joined to a single power source by one connecting-rod, an idea also taken up by his compatriot Francesco di Giorgio
Francesco di Giorgio
Francesco di Giorgio Martini was an Italian painter of the Sienese School and a sculptor, as well as being, in Nikolaus Pevsner's terms, "one of the most interesting later Quattrocento architects'" and a visionary architectural theorist; as a military engineer he executed architectural designs and...

.

Crankshafts were also described by Konrad Kyeser
Konrad Kyeser was a German military engineer, author of Bellifortis , a book on siege engines popular throughout the 15th century...

(d. 1405), Leonardo da Vinci
Leonardo da Vinci
Leonardo di ser Piero da Vinci was an Italian Renaissance polymath: painter, sculptor, architect, musician, scientist, mathematician, engineer, inventor, anatomist, geologist, cartographer, botanist and writer whose genius, perhaps more than that of any other figure, epitomized the Renaissance...

(1452–1519) and a Dutch "farmer" by the name Cornelis Corneliszoon
Cornelis Corneliszoon
Cornelis Corneliszoon van Uitgeest, or Krelis Lootjes was a Dutch windmill owner from Uitgeest who invented the wind-powered sawmill, which made the conversion of log timber into planks 30 times faster than before.-Biography:...

van Uitgeest in 1592. His wind-powered sawmill
Sawmill
A sawmill is a facility where logs are cut into boards.-Sawmill process:A sawmill's basic operation is much like those of hundreds of years ago; a log enters on one end and dimensional lumber exits on the other end....

used a crankshaft to convert a windmill's circular motion into a back-and-forward motion powering the saw. Corneliszoon was granted a patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....

for his crankshaft in 1597.

From the 16th century onwards, evidence of cranks and connecting rods integrated into machine design becomes abundant in the technological treatises of the period: Agostino Ramelli
Agostino Ramelli
Agostino Ramelli was an engineer who designed the "book wheel" or "reading wheel".During the Siege of La Rochelle , Agostino successfully engineered a mine under a bastion and breached the fortification, making him popular with his commander, Henri d'Anjou, who later became Henri III of France.In...

's The Diverse and Artifactitious Machines of 1588 alone depicts eighteen examples, a number which rises in the Theatrum Machinarum Novum by Georg Andreas Böckler
Georg Andreas Böckler
Georg Andreas Böckler was a German architect and engineer who wrote Architectura Curiosa Nova and Theatrum Machinarum Novum ....

to 45 different machines, one third of the total.

### Middle and Far East

Al-Jazari
Al-Jazari
Abū al-'Iz Ibn Ismā'īl ibn al-Razāz al-Jazarī was a Muslim polymath: a scholar, inventor, mechanical engineer, craftsman, artist, mathematician and astronomer from Al-Jazira, Mesopotamia, who lived during the Islamic Golden Age...

(1136–1206) described a crank and connecting rod system in a rotating machine in two of his water-raising machines. His twin-cylinder pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...

incorporated a crankshaft, but the device was unnecessarily complex indicating that he still did not fully understand the concept of power conversion. In China, the potential of the crank of converting circular motion into reciprocal one never seems to have been fully realized, and the crank was typically absent from such machines until the turn of the 20th century.

## Design

Large engines are usually multicylinder
Engine configuration
Engine configuration is an engineering term for the layout of the major components of a reciprocating piston internal combustion engine. These components are the cylinders and crankshafts in particular but also, sometimes, the camshaft....

to reduce pulsations from individual firing strokes
Stroke (engines)
Reciprocating motion, used in reciprocating engines and other mechanisms, is back-and-forth motion. Each cycle of reciprocation consists of two opposite motions: there is a motion in one direction, and then a motion back in the opposite direction. Each of these is called a stroke...

, with more than one piston attached to a complex crankshaft. Many small engines, such as those found in moped
Moped
Mopeds are a type of low-powered motorcycle designed to provide economical and relatively safe transport with minimal licensing requirements.Mopeds were once all equipped with bicycle-like pedals , but moped has been increasingly applied by governments to vehicles without pedals, based on their...

s or garden machinery, are single cylinder and use only a single piston, simplifying crankshaft design. This engine can also be built with no riveted seam.

### Bearings

The crankshaft has a linear axis about which it rotates, typically with several bearing journals riding on replaceable bearings
Bearing (mechanical)
A bearing is a device to allow constrained relative motion between two or more 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...

(the main bearing
Main bearing
In a piston engine, the main bearings are the bearings on which the crankshaft rotates, usually plain or journal bearings.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 pins...

s) held in the engine block. As the crankshaft undergoes a great deal of sideways load from each cylinder in a multicylinder engine, it must be supported by several such bearings, not just one at each end. This was a factor in the rise of V8 engine
V8 engine
A V8 engine is a V engine with eight cylinders mounted on the crankcase in two banks of four cylinders, in most cases set at a right angle to each other but sometimes at a narrower angle, with all eight pistons driving a common crankshaft....

s, with their shorter crankshafts, in preference to straight-8
Straight-8
The straight-eight engine or inline-eight engine is an eight-cylinder internal combustion engine with all eight cylinders mounted in a straight line along the crankcase...

engines. The long crankshafts of the latter suffered from an unacceptable amount of flex when engine designers began using higher compression ratio
Compression ratio
The 'compression ratio' of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity...

s and higher rotational speeds. High performance engines often have more main bearings than their lower performance cousins for this reason.

### Piston stroke

The distance the axis of the crank throws from the axis of the crankshaft determines the piston stroke
Stroke (engines)
Reciprocating motion, used in reciprocating engines and other mechanisms, is back-and-forth motion. Each cycle of reciprocation consists of two opposite motions: there is a motion in one direction, and then a motion back in the opposite direction. Each of these is called a stroke...

measurement, and thus engine displacement
Engine displacement
Engine displacement is the volume swept by all the pistons inside the cylinders of an internal combustion engine in a single movement from top dead centre to bottom dead centre . It is commonly specified in cubic centimeters , litres , or cubic inches...

. A common way to increase the low-speed torque of an engine is to increase the stroke, sometimes known as "shaft-stroking." This also increases the reciprocating vibration
Engine balance
Engine balance is the design, construction and tuning of an engine to run smoothly. Improving engine balance reduces vibration and other stresses and can improve the overall performance, efficiency, cost of ownership and reliability of the engine, as well as reducing the stress on other machinery...

, however, limiting the high speed capability of the engine. In compensation, it improves the low speed operation of the engine, as the longer intake stroke through smaller valve(s) results in greater turbulence and mixing of the intake charge. For this reason, even such high speed production engines as current Honda
Honda
is a Japanese public multinational corporation primarily known as a manufacturer of automobiles and motorcycles.Honda has been the world's largest motorcycle manufacturer since 1959, as well as the world's largest manufacturer of internal combustion engines measured by volume, producing more than...

engines are classified as "under square" or long-stroke, in that the stroke is longer than the diameter of the cylinder bore. As such, finding the proper balance between shaft-stroking speed and length will lead to better results.

### Engine configuration

The configuration
Engine configuration
Engine configuration is an engineering term for the layout of the major components of a reciprocating piston internal combustion engine. These components are the cylinders and crankshafts in particular but also, sometimes, the camshaft....

and number of pistons in relation to each other and the crank leads to straight
Straight engine
Usually found in four- and six-cylinder configurations, the straight engine, or inline engine is an internal-combustion engine with all cylinders aligned in one row, with no offset...

, V
V engine
A V engine, or Vee engine is a common configuration for an internal combustion engine. The cylinders and pistons are aligned, in two separate planes or 'banks', so that they appear to be in a "V" when viewed along the axis of the crankshaft...

or flat engine
Flat engine
A flat engine is an internal combustion engine with multiple pistons that move in a horizontal plane. Typically, the layout has cylinders arranged in two banks on either side of a single crankshaft and is sometimes known as the boxer, or horizontally opposed engine. The concept was patented in 1896...

s. The same basic engine block can be used with different crankshafts, however, to alter the firing order
Firing order
The firing order is the sequence of power delivery of each cylinder in a multi-cylinder reciprocating engine.This is achieved by sparking of the spark plugs in a gasoline engine in the correct order, or by the sequence of fuel injection in a Diesel engine...

; for instance, the 90° V6 engine
V6 engine
A V6 engine is a V engine with six cylinders mounted on the crankcase in two banks of three cylinders, usually set at either a right angle or an acute angle to each other, with all six pistons driving a common crankshaft...

configuration, in older days sometimes derived by using six cylinders of a V8 engine
V8 engine
A V8 engine is a V engine with eight cylinders mounted on the crankcase in two banks of four cylinders, in most cases set at a right angle to each other but sometimes at a narrower angle, with all eight pistons driving a common crankshaft....

with what is basically a shortened version of the V8 crankshaft, produces an engine with an inherent pulsation in the power flow due to the "missing" two cylinders. The same engine, however, can be made to provide evenly spaced power pulses by using a crankshaft with an individual crank throw for each cylinder, spaced so that the pistons are actually phased 120° apart, as in the GM 3800 engine. While production V8 engines use four crank throws spaced 90° apart, high-performance V8 engines often use a "flat" crankshaft with throws spaced 180° apart. The difference can be heard as the flat-plane crankshafts result in the engine having a smoother, higher-pitched sound than cross-plane (for example, IRL IndyCar Series
IndyCar Series
The IZOD IndyCar Series is the premier level of American open wheel racing. The current championship, founded by Indianapolis Motor Speedway owner Tony George, began in 1996 as a competitor to CART known as the Indy Racing League . Citing CART's increasing reliance on expensive machinery and...

compared to NASCAR Nextel Cup
NEXTEL Cup
The NASCAR Sprint Cup Series is the top racing series of the National Association for Stock Car Auto Racing . The series was originally known as the Strictly Stock Series and Grand National Series . While leasing its naming rights to R. J...

, or a Ferrari 355 compared to a Chevrolet Corvette
Chevrolet Corvette
The Chevrolet Corvette is a sports car by the Chevrolet division of General Motors that has been produced in six generations. The first model, a convertible, was designed by Harley Earl and introduced at the GM Motorama in 1953 as a concept show car. Myron Scott is credited for naming the car after...

). See the main article on crossplane
Crossplane
The crossplane or cross-plane is a crankshaft design for V8 engines with a 90° angle between the cylinder banks.The crossplane crankshaft has four crankpins, each offset at 90° from the adjacent crankpins...

crankshafts.

### Engine balance

For some engines it is necessary to provide counterweight
Counterweight
A counterweight is an equivalent counterbalancing weight that balances a load.-Uses:A counterweight is often used in traction lifts , cranes and funfair rides...

s for the reciprocating mass of each piston and connecting rod to improve engine balance
Engine balance
Engine balance is the design, construction and tuning of an engine to run smoothly. Improving engine balance reduces vibration and other stresses and can improve the overall performance, efficiency, cost of ownership and reliability of the engine, as well as reducing the stress on other machinery...

. These are typically cast as part of the crankshaft but, occasionally, are bolt-on pieces. While counter weights add a considerable amount of weight to the crankshaft, it provides a smoother running engine and allows higher RPMs to be reached.

### Rotary engines

Many early aircraft engines (and a few in other applications) had the crankshaft fixed to the airframe
Airframe
The airframe of an aircraft is its mechanical structure. It is typically considered to include fuselage, wings and undercarriage and exclude the propulsion system...

and instead the cylinders rotated, known as a rotary engine
Rotary engine
The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration, in which the crankshaft remained stationary and the entire cylinder block rotated around it...

design. Rotary engines such as the Wankel engine
Wankel engine
The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that...

are referred to as pistonless rotary engines.

In the Wankel engine
Wankel engine
The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that...

the rotors drive the eccentric shaft, which could be considered the equivalent of the crankshaft in a piston engine.

## Construction

Crankshafts can be monolithic (made in a single piece) or assembled from several pieces. Monolithic crankshafts are most common, but some smaller and larger engines use assembled crankshafts.

### Forging and casting

Crankshafts can be forged
Forging
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: '"cold," "warm," or "hot" forging. Forged parts can range in weight from less than a kilogram to 580 metric tons...

from a steel bar usually through roll forging or cast in ductile steel. Today more and more manufacturers tend to favor the use of forged crankshafts due to their lighter weight, more compact dimensions and better inherent dampening. With forged crankshafts, vanadium microalloyed steels are mostly used as these steels can be air cooled after reaching high strengths without additional heat treatment, with exception to the surface hardening of the bearing surfaces. The low alloy content also makes the material cheaper than high alloy steels. Carbon steels are also used, but these require additional heat treatment to reach the desired properties. Iron crankshafts are today mostly found in cheaper production engines (such as those found in the Ford Focus diesel engines) where the loads are lower. Some engines also use cast iron crankshafts for low output versions while the more expensive high output version use forged steel.

### Machining

Crankshafts can also be machined
Machining
Conventional machining is a form of subtractive manufacturing, in which a collection of material-working processes utilizing power-driven machine tools, such as saws, lathes, milling machines, and drill presses, are used with a sharp cutting tool to physical remove material to achieve a desired...

out of a billet
Billet (manufacturing)
Semi-finished casting products are intermediate castings produced in a foundry that need further processing before being a finished good. There are four types: ingots, billets, blooms, and slabs.-Ingot:...

, often using a bar of high quality vacuum remelted steel. Even though the fiber flow (local inhomogeneities of the material's chemical composition generated during casting) doesn’t follow the shape of the crankshaft (which is undesirable), this is usually not a problem since higher quality steels which normally are difficult to forge can be used. These crankshafts tend to be very expensive due to the large amount of material removal which needs to be done by using lathes and milling machines, the high material cost and the additional heat treatment required. However, since no expensive tooling is required, this production method allows small production runs of crankshafts to be made without high costs.

### Fatigue strength

The fatigue strength of crankshafts is usually increased by using a radius at the ends of each main and crankpin bearing. The radius itself reduces the stress in these critical areas, but since the radius in most cases are rolled, this also leaves some compressive residual stress in the surface which prevents cracks from forming.

### Hardening

Most production crankshafts use induction hardened bearing surfaces since that method gives good results with low costs. It also allows the crankshaft to be reground without having to redo the hardening. But high performance crankshafts, billet crankshafts in particular, tend to use nitridization
Nitridization
Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case hardened surface. It is predominantly used on steel, but also titanium, aluminum and molybdenum....

instead. Nitridization is slower and thereby more costly, and in addition it puts certain demands on the alloying metals in the steel, in order to be able to create stable nitrides. The advantage with nitridization is that it can be done at low temperatures, it produces a very hard surface and the process will leave some compressive residual stress in the surface which is good for the fatigue properties of the crankshaft. The low temperature during treatment is advantageous in that it doesn’t have any negative effects on the steel, such as annealing
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...

. With crankshafts that operate on roller bearings, the use of carburization
Carburization
Carburizing, spelled carburising in the UK, is a heat treatment process in which iron or steel is heated in the presence of another material which liberates carbon as it decomposes. Depending on the amount of time and temperature, the affected area can vary in carbon content...

tends to be favored due to the high Hertzian contact stresses in such an application. Like nitriding, carburization also leaves some compressive residual stresses in the surface.

### Counterweights

Some expensive, high performance crankshafts also use heavy-metal counterweights to make the crankshaft more compact. The heavy-metal used is most often a tungsten alloy but depleted uranium has also been used. A cheaper option is to use lead, but compared with tungsten its density is much lower.

## Stress on crankshafts

The shaft is subjected to various forces but generally needs to be analysed in two positions.
Firstly, failure may occur at the position of maximum bending; this may be at the centre of the crank or at either end. In such a condition the failure is due to bending and the pressure in the cylinder is maximal. Second, the crank may fail due to twisting, so the conrod needs to be checked for shear at the position of maximal twisting. The pressure at this position is the maximal pressure, but only a fraction of maximal pressure.

• Crankcase
Crankcase
In an internal combustion engine of the reciprocating type, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder, which in a multicylinder engine are usually integrated into one or several cylinder blocks...

, the housing that surrounds the crankshaft
• Bicycle crankset
Crankset
The crankset or chainset , is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain, which in turn drives the rear wheel...

• Crank (mechanism)
Crank (mechanism)
A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm...

• Brace (tool)
Brace (tool)
A brace or brace and bit is a hand tool used to drill holes, usually in wood. Pressure is applied to the top and the tool is rotated with a U-shaped grip....

• Controlled Combustion Engine
Controlled Combustion Engine
Controlled Combustion Engine is a term used by Revetec, an engine design company, to identify a type of experimental internal combustion engine designed by Brad Howell-Smith. It uses two counter-rotating cams instead of a crankshaft...

• Piston motion equations
• Hudson Motor Car Company
Hudson Motor Car Company
The Hudson Motor Car Company made Hudson and other brand automobiles in Detroit, Michigan, from 1909 to 1954. In 1954, Hudson merged with Nash-Kelvinator Corporation to form American Motors. The Hudson name was continued through the 1957 model year, after which it was dropped.- Company strategy...

, balanced crankshaft in 1916 allowed higher RPM & more power
• Camshaft
Camshaft
A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...

• Cam
Cam
A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path...