Regular piston engines are balanced so the numerous moving parts don't create too much vibration. This is usually accomplished by strategically weighting moving parts and/or timing cylinders to fire in such a way that they cancel each others momentum as much as possible. Clearly this is well done in modern piston engine vehicles, as most of them run fairly smoothly.

How are rotary engines balanced? Are they inherently balanced since there is really only one moving mass? Do they have balancer shafts like some 4 cylinder engines do?

I'm interested specifically in things with 4 wheels, but answers for motorcycle rotary engines are also interesting

  • 2
    Very carefully :o) Feb 1, 2017 at 20:25
  • @Pᴀᴜʟsᴛᴇʀ2 I don't get it.. :(
    – rana
    Feb 1, 2017 at 21:37
  • @Paulster2 - that's exactly what I thought when I read the question. :)
    – Spivonious
    Feb 1, 2017 at 21:58
  • I know the crank needs to be dynamically balanced (at least I think that's what they were doing in the video I watched). I'd bet the lobes are pretty much balanced from the get go, considering the design. Beyond that ... no clue what else might need to get balanced or taken care of. There are so few moving parts (literally, what, like three parts on a two lobe engine?) I'd bet there really isn't much to it beyond that. Feb 1, 2017 at 22:36

1 Answer 1


With a rotary engine, (the Mazda 13b specifically in my explanation) there exist two rotors that spin about the eccentric shaft. The rotors are typically arranged so that when the front most rotor is in a position where the apexes are facing (N, SE, SW) respectively, the rotor behind would be positioned where each apex is (NW, NE, S) (using compass directions for lack of a diagram). Besides the positioning, the rotary engine doesn't have pistons or any sort of mass that needs to abruptly change direction within the cycle.

So basically, when the rotors spin, thee are little other resulting forces besides a sort of frisbee effect or centrifugal force without reciprocating masses.

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