Editing Straight-four engine (section)

=== Usage of balance shafts ===
[[File:MMC Silent shafts.jpg|thumb |Mitsubishi Silent Shaft display]]

A [[balance shaft]] system is sometimes used to reduce the vibrations created by a straight-four engine, most often in engines with larger displacements. The balance shaft system was invented in 1911 and consists of two shafts carrying identical [[Eccentric (mechanism)|eccentric]] weights that rotate in opposite directions at twice the crankshaft's speed.<ref name="Nunney"/>{{refpage|pp. 42–44}} This system was patented by Mitsubishi Motors in the 1970s, introduced in the [[Mitsubishi Astron engine]] with the "Silent Shaft" name, and has since been used under licence by several other companies.<ref name="bbc1">{{cite web |url=http://www.bbc.com/autos/story/20140609-before-they-were-carmakers |title=Before they were carmakers |last=Carney |first=Dan |publisher=BBC |location=UK |date=2014-06-10 |access-date=2018-11-01}}</ref><ref name="PS-Jun89">{{cite magazine |last=Nadel |first=Brian |date=June 1989 |title=Balancing Act |magazine=Popular Science |page =52 }}</ref>

Not all large displacement straight-four engines have used balance shafts, however. Examples of relatively large engines without balance shafts include the 2.4 litre [[Citroën DS]] engine, the 2.6 litre [[Austin-Healey 100]] engine, the 3.3&nbsp;L [[Ford Model A (1927)]] engine and the 2.5&nbsp;L [[GM Iron Duke engine]]. Soviet/Russian [[Volga (automobile)|GAZ Volga]] and [[UAZ]] engines with displacements of up to 2.9 litres were produced without balance shafts from the 1950s to the 1990s, however these were relatively low-revving engines which reduces the need for a balance shaft system.<ref name="Nunney"/>{{refpage|pp. 40–44}}