Editing Flat-four engine (section)

=== Engine balance ===
The equal and opposing forces generated in a boxer-four engine result in perfect [[secondary balance]] (unlike the unbalanced vertical forces produced by inline-four engines). Boxer-four engines are therefore better suited to displacements above {{convert|2.0|L|cuin|0|abbr=on}}, since they do not require [[balance shaft]]s to reduce the secondary vibration.

In a boxer engine, each cylinder is slightly offset from its opposing pair due to the distance between the [[crankpin]] journals. This offset gives rise to a slight [[Couple (mechanics)|rocking couple]],<ref name="Wilson">{{cite book |last=Wilson |first=Hugo |title=The Encyclopedia of the Motorcycle |url=https://archive.org/details/encyclopediaofmo00wils_1 |url-access=registration |year=1995 |publisher=Dorling Kindersley |location=London, UK |isbn=0-7513-0206-6 |chapter=The A–Z of Motorcycles }}</ref>{{refpage|page=27}} but any resulting vibration is normally insufficient to require balance shafts.

As with all four-stroke engines of four cylinders or fewer, the lack of overlap in the [[power stroke (engine)|power strokes]] results in a pulsating delivery of torque to the [[flywheel]], causing a torsional vibration along the crankshaft axis.<ref>Thomson. Vibration Theory and Applications. p. 190. Dynamics of reciprocating forces. Prentice Hall Inc., USA, 1965.</ref> Such vibration, if excessive, may be minimised using a [[harmonic damper]].