Editing Camshaft (section)

=== Location in engine ===
Many early internal combustion engines used a ''cam-in-block'' layout (such [[Flathead engine|flathead]], [[IOE engine|IOE]] or [[T-head engine|T-head]] layouts), whereby the camshaft is located within the engine block near the bottom of the engine. Early flathead engines locate the valves in the block and the cam acts directly on those valves.  In an overhead valve engine, which came later, the [[Tappet#Internal combustion engines|cam follower]] presses on a [[pushrod]] which transfers the motion to the top of the engine, where a rocker opens the intake/exhaust valve.<ref name="mechanicbase.com">{{Cite web|last=Sellén|first=Magnus|date=2019-07-24|title=DOHC Vs. SOHC - What's The Difference Between Them?|url=https://mechanicbase.com/engine/dohc-vs-sohc/|access-date=2020-06-10|website=Mechanic Base|language=en-US}}</ref> Although largely replaced by SOHC and DOHC layouts in modern automobile engines, the older overhead valve layout is still used in many industrial engines, due to its smaller size and lower cost.

As engine speeds increased through the 20th century, [[Overhead camshaft engine#Single overhead camshaft (SOHC)|single overhead camshaft]] (SOHC) engines— where the camshaft is located within the [[cylinder head]] near the top of the engine— became increasingly common, followed by [[Overhead camshaft engine#Double overhead camshaft|double overhead camshaft]] (DOHC) engines in more recent years. For OHC and DOHC engines, the camshaft operates the valve directly or via a short rocker arm.<ref name="mechanicbase.com"/>

The valvetrain layout is defined according to the number of camshafts per cylinder bank. Therefore, a V6 engine with a total of four camshafts - two camshafts per cylinder bank - is usually referred to as a ''double overhead camshaft'' engine (although colloquially they are sometimes referred to as "quad-cam" engines).<ref>{{cite web |title=What is Quad-cam engine? |url=http://carspector.com/dictionary/Q/quad-cam-engine/ |website=www.carspector.com |access-date=7 June 2020}}</ref>