Touring: CB1100 vs. F800GT

[the Ferret]

Please tell me there is an annoy buzz right at your favorite cruising speed......

Chief, it's a parallel twin with a 360° firing order. Are you new to motorcycling?

"...annoy buzz..."? That's a rather subjective characterization. It's only annoying if you despise torque and horsepower on tap in virtually every gear at virtually every speed and don't like the inherent visceral mechanical nature of motorcycles.

I'm new to motorcycling. What's a 360° firing order? Does it mean a cylinder goes <BANG> every time the crankshaft goes around?

I also like the dealer's sticker in one of the early pictures that says "Sold. Sorry."

Sorry? I'll bet they're not. Why doesn't it say "Sold. Great news!"

[flynrider]

Please tell me there is an annoy buzz right at your favorite cruising speed......

Chief, it's a parallel twin with a 360° firing order. Are you new to motorcycling?

"...annoy buzz..."? That's a rather subjective characterization. It's only annoying if you despise torque and horsepower on tap in virtually every gear at virtually every speed and don't like the inherent visceral mechanical nature of motorcycles.

I'm new to motorcycling. What's a 360° firing order? Does it mean a cylinder goes <BANG> every time the crankshaft goes around?

I also like the dealer's sticker in one of the early pictures that says "Sold. Sorry."

Sorry? I'll bet they're not. Why doesn't it say "Sold. Great news!"

Pretty much. From a vibration aspect having a cylinder fire on each revolution also means that they are both traveling up and down in unison. When one is firing, the other is on the intake stroke, but they're both moving up and down together which leads to a primary vibration. I've ridden parallel twins that had counter balancers that supposedly offset this vibration, but they tended to have minimal effect.

[Django]

I rode both, a co-rotating Yamaha XS650 and a counter-rotating Honda CB500T.

Caused by the asymetric firing of the counter-rotating twin, the CB500T had a really great sound: wrooom!

Co-rotating twins sound rather boring: r-r-r-r-r-r-r-r-r-r

[Cormanus]

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?

[Stichill_imp]

Husqvarna took the same parallel twin engine and put it in their Nuda, but with an offset the crank of -45 deg (315 deg). This gives it the same cadence as a Harley.

[rboe]

I'd feel better if there was a something annoying about the bike.

[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.

[Cormanus]

Thanks again, Flyn. I know more tonight than I did this morning.

[JF Coastal_imp]

Congratulations Stichill. ! That's a great looking bike, have fun with it. Hope to see some ride reports

[the Ferret]

Cylinders can be made to fire anywhere in the rotataion according to ignition timimg. Check out the firing order on the Yamaha Cross plane "big bang" engines sometime

http://en.wikipedia.org/wiki/Big-bang_firing_order

I had 3 Yamaha XS 650 twins 73, 79 and 81 and they were indeed shakers. You could walk them across the garage floor by revving them up on the centerstand. Loved them though. I never saw the Yamahas crack fenders or lic plate brackets or loosen and have parts fall off like I did the British twins though.

I also had 160, 305, 350 and 450 Honda twins and a 03 Triumph Bonneville twin. The Triumph with the counter balancer was amazingly smooth. Smoother than my V65 longitudinal V4 Honda and my V4 transverse ST Honda.