Editing Connecting rod

{{Short description|Piston engine component which connects the piston to the crankshaft}}
[[File:Drawing of a connecting rod in an automobile engine.jpg|thumb|Typical design of automobile engine connecting rod]]
[[File:Bielle.jpg|thumb|Typical aluminium rod (left), oil drip rod (centre), steel rod (right)]]
A '''connecting rod''', also called a ''''con rod'''',<ref>{{cite web |title=Connecting Rods and Bearings |url=https://www.enginebuildermag.com/2010/10/connecting-rods-and-bearings/ |website=Engine Builder Magazine |access-date=21 August 2022 |date=25 October 2010}}</ref><ref>{{cite web |title=Con rods link pistons and crankshaft {{!}} Perkins |url=https://www.perkins.com/en_GB/aftermarket/overhaul/overhaul-components/major-components/con-rods.html |website=www.perkins.com |access-date=21 August 2022 |language=en}}</ref><ref>{{cite web |title=What is Con Rod? |url=https://accurateengg.com/what-is-con-rod/ |website=accurateengg.com |access-date=21 August 2022 |date=22 November 2019 |archive-date=5 February 2023 |archive-url=https://web.archive.org/web/20230205193733/https://accurateengg.com/what-is-con-rod/ |url-status=dead }}</ref> is the part of a [[reciprocating engine|piston engine]] which connects the [[piston]] to the [[crankshaft]]. Together with the [[crank (mechanism)|crank]], the connecting rod converts the [[reciprocating motion]] of the piston into the rotation of the crankshaft.<ref name="Yamagata 2005 p. 207">{{cite book | last=Yamagata | first=H. | title=The Science and Technology of Materials in Automotive Engines | publisher=Elsevier Science | series=Woodhead Publishing in materials The science and technology of materials in automotive engines | year=2005 | isbn=978-1-84569-085-4 | url=https://books.google.com/books?id=7rekAgAAQBAJ | page=207 }}</ref> The connecting rod is required to transmit the compressive and tensile forces from the piston. In its most common form, in an [[internal combustion engine]], it  allows pivoting on the piston end and rotation on the shaft end.

The predecessor to the connecting rod is a mechanic linkage used by water mills to convert rotating motion of the water wheel into reciprocating motion.<ref>{{Cite book|title = Steam Automobile Vol. 13, No. 3|url = https://books.google.com/books?id=kaexwddMdNoC|publisher = SACA|language = en|first1 = Robert L.|last1 = Lyon}}</ref>

The most common usage of connecting rods is in [[internal combustion engine]]s or on [[steam engine]]s.
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== Origins ==
[[File:Römische Sägemühle.svg|thumb|right|[[Hierapolis sawmill]] schematic]]

A connecting rod crank has been found in the Celtic Oppida at [[Paule]] in Brittany, dated to 69 BC.<ref>[https://patrimoine.lamayenne.fr/jublains/wp-content/uploads/2022/07/2016_DP_Exposition_Premieres_villes_gauloises_Jublains.pdf L’exposition « Les Premières Villes de l’ouest », en quelques mots…]</ref>{{Vn|date=March 2025}}

The predecessor to the connecting length is the [[Linkage (mechanical)|mechanical linkage]] used by [[List of Roman watermills|Roman-era watermills]]. An early example of this linkage has been found at the late 3rd century [[Hierapolis sawmill]] in Roman Asia (modern Turkey) and the 6th century saw mills at [[Ephesus]] in Asia Minor (modern Turkey) and at [[Gerasa]] in Roman Syria. The [[Crank (mechanism)|crank]] and connecting rod mechanism of these machines converted the rotary motion of the waterwheel into the linear movement of the saw blades.<ref name="Ritti, Grewe, Kessener 2007, 161">{{Cite book |last1 = Ritti |first1 = Tullia | last2 = Grewe | first2 = Klaus | last3 = Kessener | first3 = Paul | year = 2007 | title = A Relief of a Water-powered Stone Saw Mill on a Sarcophagus at Hierapolis and its Implication | periodical = Journal of Roman Archaeology | volume = 20 |page=161 |quote=Because of the findings at Ephesus and Gerasa the invention of the crank and connecting rod system has had to be redated from the 13th to the 6th c; now the Hierapolis relief takes it back another three centuries, which confirms that water-powered stone saw mills were indeed in use when it change the world of engines. [[Ausonius]] wrote his Mosella.}}</ref>

An early documentation of the design occurred sometime between 1174 and 1206 AD in the [[Artuqids|Artuqid State]] (modern Turkey), when inventor [[Al-Jazari]] described a machine which incorporated the connecting rod with a crankshaft to pump water as part of a water-raising machine,<ref>{{cite web |author=Ahmad Y Hassan |author-link=Ahmad Y Hassan |url=http://www.history-science-technology.com/Notes/Notes%203.htm |title=The Crank-Connecting Rod System in a Continuously Rotating Machine}}</ref><ref>{{citation |title=Islam and Science, Medicine, and Technology |author=Sally Ganchy |author2=Sarah Gancher |publisher=The Rosen Publishing Group |year=2009 |isbn=978-1-4358-5066-8 |page=41 |url-access=registration |url=https://archive.org/details/islamsciencemedi0000ganc }}</ref> though the device was more complex than typical crank and connecting rod designs.<ref name="White Jr. 1962">{{Cite book | last=White | first=Lynn Jr. | author-link = Lynn Townsend White, Jr. | title = Medieval Technology and Social Change | place = Oxford | year = 1962 | publisher = At the Clarendon Press | quote=However, that al-Jazari did not entirely grasp the meaning of the crank for joining reciprocating with rotary motion is shown by his extraordinarily complex pump powered through a cog-wheel mounted eccentrically on its axle.}}</ref>{{refpage|page=170}} There is also documentation of cranks with connecting rods in the sketch books of [[Taccola]] from [[Renaissance Italy]] and 15th century painter [[Pisanello]].<ref name="White Jr. 1962"/>{{refpage|page=113}}
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== Steam engines ==
{{multiple image
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| direction         = vertical
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| image1            = Twin Beam Engine.jpg
| caption1          = [[Beam engine]] with twin connecting rods (almost vertical) between the horizontal beam and the flywheel
| image2            = Walschaerts valve gear.jpg
| caption2          = Steam locomotive connecting rod (between the piston and the rear wheel; the largest rod visible)
}}

The 1712 [[Newcomen atmospheric engine]] (the first steam engine) used chain drive instead of a connecting rod, since the piston only produced force in one direction.<ref>{{cite web|title = Steam Locomotive Glossary|url = http://www.railway-technical.com/st-glos.shtml|website = www.railway-technical.com|access-date = 2016-02-05|archive-url = https://web.archive.org/web/20080128230325/http://www.railway-technical.com/st-glos.shtml|archive-date = 2008-01-28|url-status = dead}}</ref> However, most steam engines after this are [[double-acting cylinder|double-acting]], therefore the force is produced in both directions, leading to the use of a connecting rod. The typical arrangement uses a large sliding bearing block called a [[crosshead]] with the hinge between the piston and connecting rod placed outside the cylinder, requiring a seal around the [[piston rod]].<ref>{{cite book| url=https://books.google.com/books?id=4iYeCgAAQBAJ| title=The Victorian Steam Locomotive: Its Design & Development 1804-1879| pages=27–28| first1=G.D.| last1=Dempsey| first2=D. Kinnear| last2=Clark| publisher=Pen & Sword Transport| year=2015| location=Barnsley, England| isbn=978-1-47382-323-5| via=Google Books}}</ref>
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Expansion on crossheads, maybe Watt parallel motion
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In a [[steam locomotive]], the cranks are usually mounted directly on the [[driving wheel]]s. The connecting rod is used between the crank pin on the wheel and the crosshead (where it connects to the [[piston rod]]).<ref>{{cite book| url=https://books.google.com/books?id=_7lJAAAAIAAJ| pages=74–78| title=Steam Locomotive Construction and Maintenance| publisher=The Locomotive Publishing Co. Ltd.| location=London| series=Pitman's Technical Primer Series| editor-first=R.E.| editor-last=Neale| first=E.L.| last=Ahrons| year=1921| via=Google Books}}</ref> On smaller steam locomotives, the connecting rods are usually of rectangular cross-section;<ref>{{cite book| url=https://books.google.com/books?id=1A4iiGAz628C&q=steam+locomotive+connecting+rod&pg=PA185| page=185| title=A History of the American Locomotive: Its Development, 1830-1880| first=John H. Jr.| last=White| publisher=Dover Publications| location=New York| year=1979| isbn=9780486238180| via=Google books}}</ref> however, marine-type rods of circular cross-section have occasionally been used.

On [[paddle steamer]]s, the connecting rods are called 'pitmans' (not to be mistaken for [[pitman arm]]s).

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== Internal combustion engines ==
[[File:Piston and connecting rod.jpg|thumb|upright=0.75|Connecting rod and piston from a car engine]]

A connecting rod for an internal combustion engine consists of the 'big end', 'rod' and 'small end'. The small end attaches to the [[gudgeon pin]] (also called 'piston pin' or 'wrist pin' in the U.S.), which allows for rotation between the connecting rod and the piston. Typically, the big end connects to the [[crankpin]] using a [[plain bearing]] to reduce friction; however, some smaller engines may instead use a [[rolling-element bearing]], in order to avoid the need for a pumped lubrication system. Connecting rods with rolling element bearings are typically a one piece design where the crankshaft must be pressed together through them, rather than a two piece design that can be bolted around the journal of a one piece crankshaft.{{cn|date=August 2022}}

Typically there is a pinhole bored through the bearing on the big end of the connecting rod so that lubricating oil squirts out onto the thrust side of the cylinder wall to lubricate the travel of the pistons and [[piston ring]]s.

A connecting rod can rotate at both ends, so that the angle between the connecting rod and the piston can change as the rod moves up and down and rotates around the [[crankshaft]].

=== Materials ===
The materials used for connecting rods widely vary, including carbon steel, iron base sintered metal, micro-alloyed steel, spheroidized graphite cast iron.<ref name="Yamagata 2005 p. 7">{{harvnb|Yamagata|2005|p=7}}</ref> In mass-produced automotive engines, the connecting rods are most usually made of [[steel]]. In high performance applications, "billet" connecting rods can be used, which are machined out of a solid [[Billet (manufacturing)|billet]] of metal, rather than being [[casting|cast]] or forged.

Other materials include  T6-[[2024 aluminium alloy]] or T651-[[7075 aluminium alloy]], which are used for lightness and the ability to absorb high impact at the expense of durability. [[Titanium]] is a more expensive option which reduces the weight. [[Cast iron]] can be used for cheaper, lower performance applications such as motor scooters.
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=== Failure during operation ===
[[File:Biella rotta per fatica.jpg |thumb|right|upright=0.75|Connecting rod that initially failed through fatigue, then was further damaged from impact with the crankshaft]]

During each rotation of the crankshaft, a connecting rod is often subject to large and repetitive forces: [[shear force]]s due to the angle between the piston and the crankpin, [[Compression (physics)|compression forces]] as the piston moves downwards, and [[Tension (physics)|tensile forces]] as the piston moves upwards.<ref>{{cite web |title=Causes of Failure With a Connecting Rod |url=https://itstillruns.com/causes-failure-connecting-rod-7260672.html |website=www.itstillruns.com |access-date=21 September 2019 |language=en}}</ref> These forces are proportional to the engine speed (RPM) squared.

Failure of a connecting rod, often called "throwing a rod", often forces the broken rod through the side of the crankcase and thereby renders the engine irreparable.<ref>{{cite web|title = What does it mean to "throw a rod"?|url = http://www.cartalk.com/content/what-does-it-mean-throw-rod|website = Car Talk|access-date = 2016-02-05|date = April 1990}}</ref> Common causes of connecting rod failure are tensile failure from high engine speeds, the impact force when the piston hits a valve (due to a valvetrain problem), rod bearing failure (usually due to a lubrication problem), or incorrect installation of the connecting rod.<ref>{{cite web |title=Preventing Connecting Rod Failures |url=https://www.enginebuildermag.com/2017/03/preventing-connecting-rod-failures/ |website=www.enginebuildermag.com |access-date=21 September 2019 |date=15 March 2017}}</ref><ref>{{cite web |title=How to eliminate connecting rod failures |url=https://www.hotrod.com/articles/ctrp-0311-connecting-rods/ |website=www.hotrod.com |date=November 2003 |access-date=21 September 2019}}</ref><ref>{{cite web |title=Probable Cause of Most Rod Failures |url=https://arcracing.blogspot.com/1999/07/probable-cause-of-most-rod-failures.html |website=www.arcracing.blogspot.com |access-date=21 September 2019 |date=1 June 1999}}</ref><ref>{{cite web|title = Emerson Bearing Extreme Applications |url = http://www.emersonbearing.com/news-articles/extreme-applications|website = www.emersonbearing.com |access-date = 2016-02-05|language = en-US}}</ref>
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=== Cylinder wear ===
The sideways force exerted on the piston through the connecting rod by the [[crankshaft]] can cause the [[cylinder (engine)|cylinders]] to wear into an oval shape. This significantly reduces engine performance, since the circular [[piston ring]]s are unable to properly seal against the oval-shaped cylinder walls.

The amount of sideways force is proportional to the angle of the connecting rod, therefore longer connecting rods will reduce the amount of sideways force and engine wear. However, the maximum length of a connecting rod is constrained by the engine block size; the [[Stroke (engine)|stroke length]] plus the connecting rod length must not result in the piston travelling past the top of the engine block.
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=== Master-and-slave rods ===
{{multiple image
| align             = right
| direction         = vertical
| width             = 220
| image1            = Radial_engine_timing-small.gif
| caption1          = Operating principle of a radial engine
| image2            = Renault 190HP conrods fig5.jpg
| caption2          = Master–slave rods in the 1916–1918 [[Renault 8G]] V8 aircraft engine
}}
[[Radial engine]]s typically use master-and-slave connecting rods, whereby one piston (the uppermost piston in the animation), has a master rod with a direct attachment to the crankshaft. The remaining pistons pin their connecting rods' attachments to rings around the edge of the master rod.

Multi-bank engines with many cylinders, such as [[V12 engine]]s, have little space available for many connecting rod journals on a limited length of crankshaft. The simplest solution, as used in most road car engines, is for each pair of cylinders to share a [[crank journal]], but this reduces the size of the rod bearings and means that matching (i.e. opposite) cylinders in the different banks are slightly offset along the crankshaft axis (which creates a [[Couple (mechanics)|rocking couple]]). Another solution is to use master-and-slave connecting rods, where the master rod also includes one or more ring pins which are connected to the big ends of slave rods on other cylinders. A drawback of master–slave rods is that the stroke lengths of all slave pistons not located 180° from the master piston will always be slightly longer than that of the master piston, which increases vibration in V engines.

One of the most complicated examples of master-and-slave connecting rods is the 24-cylinder [[Junkers Jumo 222]] experimental airplane engine developed for World War II. This engine consisted of six banks of cylinders, each with four cylinders per bank. Each "layer" of six cylinders used one master connecting rod, with the other five cylinders using slave rods.<ref>{{Cite web |url=http://www.flugzeug-lorenz.de/index.php?eID=tx_cms_showpic&file=uploads%2Fpics%2FYY_169-1_Jumo222_Stirnschnitt.jpg&width=10000m&height=10000m&bodyTag=%3Cbody%20style%3D%22margin%3A0%3B%20background%3A%23fff%3B%22%3E&wrap=%3Ca%20href%3D%22javascript%3Aclose%28%29%3B%22%3E%20%7C%20%3C%2Fa%3E&md5=3a4da1957d3bd583a511bb5044efc2d8 |title=Image |access-date=2014-07-11 |archive-date=2014-04-13 |archive-url=https://web.archive.org/web/20140413224411/http://www.flugzeug-lorenz.de/index.php?eID=tx_cms_showpic&file=uploads%2Fpics%2FYY_169-1_Jumo222_Stirnschnitt.jpg&width=10000m&height=10000m&bodyTag=%3Cbody%20style%3D%22margin%3A0%3B%20background%3A%23fff%3B%22%3E&wrap=%3Ca%20href%3D%22javascript%3Aclose%28%29%3B%22%3E%20%7C%20%3C%2Fa%3E&md5=3a4da1957d3bd583a511bb5044efc2d8 |url-status=dead }}</ref> Approximately 300 test engines were built, but the engine did not reach production.
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=== Fork-and-blade rods ===
[[File:Forked connecting rods (Autocar Handbook, 13th ed, 1935).jpg|thumb|upright|Fork and blade rods]]
{{refimprove section|date=August 2022}}
Fork-and-blade rods, also known as "split big-end rods", have been used on [[V-twin engine|V-twin]] motorcycle engines and [[V12 engine|V12]] aircraft engines.<ref>{{cite web |title=Drysdale Godzilla V-Twin |url=https://thekneeslider.com/drysdale-godzilla-v-twin/ |website=thekneeslider.com |access-date=26 September 2019}}</ref> For each pair of cylinders, a "fork" rod is split in two at the big end and the "blade" rod from the opposing cylinder is thinned to fit into this gap in the fork. This arrangement removes the [[couple (mechanics)|rocking couple]] that is caused when cylinder pairs are offset along the crankshaft.

A common arrangement for the big-end bearing is for the fork rod to have a single wide bearing sleeve that spans the whole width of the rod, including the central gap. The blade rod then runs, not directly on the crankpin, but on the outside of this sleeve. This causes the two rods to oscillate back and forth (instead of rotating relative to each other), which reduces the forces on the bearing and the surface speed. However, the bearing movement also becomes reciprocating rather than continuously rotating, which is a more difficult problem for lubrication.

Notable engines to use fork-and-blade rods include the [[Rolls-Royce Merlin]] V12 aircraft engine, [[Electro-Motive Diesel|EMD]] two-stroke Diesel engines, and various [[Harley-Davidson engine timeline|Harley Davidson]] V-twin motorcycle engines.

== See also ==
{{Commons category|Connecting rods}}
*[[Hydrolock]]
*[[List of auto parts]]
*[[Steam locomotive components]]

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== References ==
{{Reflist|30em}}

{{Automotive engine|state=expanded}}
{{Steam engine configurations|state=expanded}}
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[[Category:Engine technology]]
[[Category:Locomotive parts]]
[[Category:Linkages (mechanical)]]