Touring: CB1100 vs. F800GT

[flynrider]

Thank you, Flyn. And you Django. I was writing and figuring while you were posting.

Funny how people's brains work. I've always had a very rudimentary idea of how an engine works, but I'd never really tried to visualize it. I find incredibly hard—the imaginative equivalent of patting my head and rubbing my tummy.

Am I right that the alternative is called a 180° firing order? One piston goes up as the other goes down? Won't that result in a rotation where there's a <BANG> on two consecutive half turns and then nothing for a full turn? That would bring about its own vibration issues too, wouldn't it?

180 degrees is another alternative design. While the power pulses are uneven, the primary vibration issue (from the movement of the pistons) pretty much disappears. The 180 degree system was used on the smaller CBs originally. Then Honda seemed to favor the 360s for awhile (late 70s to 80s), now they've gone back to 180 degrees for all the parallel twins except for the CTX700. One of the benefits of the 360 twins was that a single ignition system could serve both cylinders (one set of points, one coil). The 180s required separate systems for each cylinder.

A third design is the 270 degree crank. This provides a loping rhythm, much like a 90 degree v-twin.

To keep this somewhat related to the thread, the BMW F800 twin is a 360 design and utilizes a third connecting rod-like appendage on the crankshaft between the cylinders as a counterbalance measure. Like so :



The shakiest twin I ever rode was my friends Yammie XS650 twin. Originally a 360 degree engine, he converted it to a "Twingle", where both cylinders fired together. Technically a 720 degree twin. It could shake the fillings from your teeth, but it had enough torque to tow a car.