With a 270º phase crank, eliminating primary vibration through the mutually reciprocating motion of pistons between two cylinders is theoretically impossible; however, secondary vibration can be eliminated in this way. By adding a uniaxial primary balancer, however, it is possible to eliminate both the primary and secondary vibrations with a 270º phase crank.
Incidentally, when a balancer is uniaxial, a primary coupling vibration proportionate to the distance between the crank and the balancer shaft remains, but if a second axis is introduced using a biaxial primary balancer, it is possible to eliminate this vibration. Since the 270º phase crank does not generate any secondary vibration, elimination of the primary vibration allows the engine to have as little vibration as the CBR1000RR's in-line, 4- cylinder engine with a secondary balancer attached or the GL1800 GOLD WING's horizontally opposed, 6-cylinder engine.
However, in order to achieve the emotional comfort of a slightly rough throb and satisfy the development concept of a "ride to suit mature tastes," the team made a deliberate decision keep the vibration and go with the uniaxial primary balancer instead of its vibration-eliminating biaxial cousin.
The piston uses vertical motion and the crank uses rotary motion. Furthermore, the rotational force working on the crank allows it to move laterally, which generates lateral vibration (Figure 1).
Even if the vibration generated through vertical motion of the piston is cancelled by the crank motion, the lateral vibration of the rotating crank remains. Therefore, a balancer that partitions the crank mass in two is set and rotated in the opposite direction, thus canceling out the lateral vibration of the crank. (Figure 2)