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Hazelton, Kansas | Ben,
I assumed Randy was talking about a parallel twin with a 180 degree crank (eg Johnny poppers and many motorcycles). Both pistons are at the same point in the stroke only at 90 and 270 degrees.
If you’re talking about a boxer (opposed twin), then the piston accelerations cancel out. Except for the couple.
Each piston undergoes different accelerations during the first 90 degrees than the second. The “secondary” component of those accelerations creates forces that add, instead of cancel, in a 4-stroke 4-cyl in-line.
Regards.
MDS
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4 cylinder engines and balancers-engine theory
