Editing Cylinder head

{{short description|Component of an internal combustion engine}}
{{multiple image
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 | image1     = K20 head.jpg
 | caption1   = Side view of a [[Dual overhead camshaft|DOHC]] cylinder head (with the valves and camshafts installed)
 | image2     = Cylinderhead.JPG
 | caption2   = Underside of a [[Overhead valve engine|OHV]] cylinder head (with the valves installed)
}}

In a [[Reciprocating engine|piston engine]], the '''cylinder head''' sits above the [[cylinder (engine)|cylinders]],<ref name="Wright 2015 p. 310">{{cite book | last=Wright | first=G. | title=Fundamentals of Medium/Heavy Duty Diesel Engines | publisher=Jones & Bartlett Learning | year=2015 | isbn=978-1-284-06705-7 | url=https://books.google.com/books?id=s5_OCwAAQBAJ&pg=PA310 | access-date=2020-11-07 | page=310}}</ref> forming the roof of the [[combustion chamber]]. In [[sidevalve engine]]s the head is a simple plate of metal containing the [[spark plug]]s and possibly [[Air-cooled engine|heat dissipation fins]]. In more modern [[overhead valve engine|overhead valve]] and [[overhead camshaft engine|overhead camshaft]] engines, the head is a more complicated metal block that also contains the inlet and exhaust passages, and often [[Radiator (engine cooling)|coolant passages]], [[Valvetrain]] components, and  [[Fuel_injection#Direct injection systems|fuel injectors]].

== Number of cylinder heads ==
A piston engine typically has one cylinder head per [[Engine_configuration#Multiple_cylinder_banks|bank of cylinders]]. 

Most modern engines with a [[straight engine|"straight" (inline) layout]] today use a single cylinder head that serves all the cylinders. 

Engines with a [[V engine|"V" layout]] or [[flat engine|"flat" layout]] typically use two cylinder heads (one for each [[cylinder bank]]), however a small number of 'narrow-angle' V engines (such as the Volkswagen [[VR5 engine|VR5]] and [[VR6 engine|VR6]] engines) use a single cylinder head spanning the two banks. 

Most [[radial engine]]s have one head for each cylinder, although this is usually of the [[monobloc engine#Cylinder head|monobloc]] form wherein the head is made as an integral part of the cylinder. This is also common for motorcycles, and such head/cylinder components are referred to as ''barrels''.

Some engines, particularly medium- and large-capacity [[diesel engine]]s built for industrial, marine, power generation, and heavy traction purposes (large trucks, [[locomotive]]s, [[heavy equipment]], etc.) have individual cylinder heads for each cylinder. This reduces repair costs as a single failed head on a single cylinder can be changed instead of a larger, much more expensive unit fitting all the cylinders.  Such a design also allows engine manufacturers to easily produce a 'family' of engines of different layouts and/or cylinder numbers without requiring new cylinder head designs.

== Design ==
{{refimprove|section|date=March 2022}}

==Engine/valvetrain configurations==

{| class="wikitable" style="text-align:left"
|-
! Engine type	<br/> (in chronological order)!! [[Camshaft]] <br/> location !! Intake [[Poppet_valve#Usage_in_internal_combustion_engines|valves]] <br/> location !! Exhaust [[Poppet_valve#Usage_in_internal_combustion_engines|valves]] <br/> location
|-
| '''[[Sidevalve engine|Sidevalve]]<br/>(flathead)''' || Block || Block	|| Block
|-
| '''[[IOE engine|Inlet over exhaust]]<br/> (IOE)''' || Block 	|| Head		|| Block
|-
| '''[[Overhead valve engine|Overhead valve]] <br/> (OHV)''' || Block	|| Head		|| Head
|-
| '''[[Overhead camshaft engine|Overhead camshaft]] <br/> (OHC)''' || Head		|| Head 	|| Head
|}

=== Sidevalve engines ===
In a [[flathead engine|flathead]] (''sidevalve'') engine, all of the [[valvetrain]] components are [[cam-in-block|contained within the block]], therefore the head is usually a simple plate of metal bolted to the top of the [[engine block]]. Sidevalve engines were once universal but are now largely obsolete in automobiles, found almost exclusively in small engines such as lawnmowers, weed trimmers and chainsaws.

===Intake over exhaust (IOE) engines===
[[IOE engine|Intake Over Exhaust]] (IOE) engines combined elements of the sidevalve and overhead valve designs. Used extensively in American motorcycles in the early 1900s, the IOE engine remained in production in limited numbers until the 1990s. IOE engines are more efficient than sidevalve engines, but also more complex, larger and more expensive to manufacture.

=== Overhead engines (OHV & OHC)===
In an [[overhead valve engine|overhead valve]] (OHV) or [[overhead camshaft engine|overhead camshaft]] (OHC) engine, the cylinder head contains several airflow passages called ''ports'';  intake ports deliver the fuel+air intake charge from the [[intake manifold]] to the [[combustion chamber]], and exhaust ports route combustion waste gases out the combustion chamber to the [[exhaust manifold]].  [[poppet valve|Valves]] open and close the ports, with the intakes offset fore-and-aft from the exhausts. The head also contains the [[spark plug]]s, and on [[Internal combustion engine cooling#Liquid cooling|water-cooled]] engines, the coolant passages.

==== Overhead valve (OHV) engines ====
A single [[camshaft]] located in the engine block uses [[pushrod]]s and [[rocker arm]]s to actuate all the valves. 

OHV engines are typically more compact than equivalent OHC engines, and fewer parts mean cheaper production, but they have largely been replaced by OHC designs, except in some American V8 engines.

====Overhead camshaft (OHC) engines ====
An [[Overhead camshaft engine|overhead camshaft]] (OHC) engine locates the camshaft(s) in the cylinder head above the combustion chamber. Eliminating pushrods lessens valvetrain inertia and provides space for optimized port designs, both providing increased power potential.

In a [[Overhead camshaft engine#Single_overhead_camshaft_(SOHC)|single overhead camshaft]] (SOHC) engine, the camshaft may be seated centrally between valve rows, or directly above a single row of valves (replacing rocker arm actuation with [[Tappet#Overhead cam engines|tappets]]). SOHC engines were widely from the 1960s to 1990s. (eliminating pushrods but still utilizing rocker arms)

[[Overhead camshaft engine#Double_overhead_camshaft_(DOHC)|Double overhead camshaft]] (DOHC) engines seat a camshaft directly above each row of offset valves (intakes inboard, exhausts outboard).<ref>{{cite web |title=FORD DuraTec Engine 3D Simulation(18) - Dailymotion Video |url=https://www.dailymotion.com/video/xaafuy_ford-duratec-engine-3d-simulation-1_tech |website=www.dailymotion.com |access-date=27 March 2022 |language=en |date=27 August 2009}}</ref>  DOHC designs allow optimal [[crossflow cylinder head|crossflow]] positioning of valves to provide higher-[[RPM]] operation. They are typically larger in size (especially width) than equivalent OHV or SOHC engines. Even though more components raise production costs, DOHC engines seen widespread use in automobile engines since the 1990s. 

==Gallery==
<gallery mode="packed" heights="200px" perrow="3" style="text-align:left">
Image:DOHC-Zylinderkopf-Schnitt.jpg |[[Double overhead camshaft|DOHC]] head- cutaway view
Image:Head D15A3.JPG|[[overhead camshaft#Single overhead camshaft (SOHC)|SOHC]] [[Honda D engine#D15A3|Honda D15A3]] engine
Image:Malossi 70cc Morini cylinder head.jpg|[[Flathead engine|Flathead]] head for a [[Moto Morini]] scooter (bottom top piece on left, top piece on right)
Image:Suzuki-GS550-DOHC.jpg|[[Double overhead camshaft|DOHC]] head for an air-cooled [[Suzuki GS series|Suzuki GS550]] engine
Image:Cylinder-head.jpg|[[Overhead valve engine|OHV]] head for a [[GMC (General Motors division)|GMC]] van (view of underside, with valves and exhaust manifold also visible)
</gallery>

== See also ==
{{Commons category| 1=Cylinder heads}}
* [[Crossflow cylinder head]]
* [[Reverse-flow cylinder head]]
* [[Head gasket]]
* [[Junk head]]
* [[Monobloc head]]
* [[Flathead engine]]
* [[T-head engine]]

==References==
{{reflist}}
{{Portal|Cars}}

{{Internal combustion engine}}

[[Category:Cylinder head| ]]
[[Category:Engine technology]]