Touring: CB1100 vs. F800GT

[emptysea]

Love the new bike....I will keep an eye out for it in the Ozarks. Just a few weeks away

[Lord Popgun]

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?

Cormanus, I found this on another site. I didn't google it, someone else did.
Ask and Wikipedia comes to the rescue:
Most British four-stroke cycle parallel twins engines had a crank angle of 360°, which means that both pistons are always in the same position as each other and move in same direction. This leads to a working cycle every 360°. The mechanical balance of this design is no better than that of a similar displacement single-cylinder engine, because the forces of both cylinders are compounded; however, the advantage is that the firing is regular, with one cylinder firing each revolution of the crankshaft rather than every second revolution.

Japanese manufacturers have made four-stroke engines in both the 360° and 180° designs. The 180° crankshaft has superior primary balance at the cost of a rocking couple. Also, the 180° design has uneven firing, resulting in these engines having a distinctive exhaust note similar to 45° v-twin harleys (differences in pitch due to significantly different capacities notwithstanding) . In such an engine, the left cylinder fires, then 180° later the right cylinder fires, then the engine rotates 540° before the left cylinder again fires.

An advantage of 360° engines, given their even firing order with corresponding even pulses in the intake tract, is their suitability to a single carburetor. This fact was exploited by Triumph, BSA, and Honda in the CA series. ( also a 360 crank can use a single set of points with a dual output coil)

Many small motorcycles of less than 250cc use the 360° crankshaft, examples being the Honda CB92, the Honda CB160 and its many derivatives, and the more recent Honda CM185 and its derivatives. Likewise, the Honda CA72 and CA77 models used 360° crankshafts.

Larger parallel twins, over 500cc, also use 360° crankshafts. Yamaha, in particular, has numerous models with this configuration, the XS650 and TX650 of 1970-1983 being well-known examples. Most parallel twins greater than 500cc designed after 1973 featured balance shafts, the Yamaha TX750 being an early example.

Honda models in the 250cc to 500cc range, very common in the 1960s and 1970s, used 180° crankshafts. Examples of such engines are found in the CB72 and CB77, CB250 and CB350, CB360, CB450 and CB500. The Yamaha TX500, introduced in 1973 also used a 180° crankshaft, although it featured a balance shaft. The Suzuki GS400, introduced in 1977, featured a 180° crankshaft and a balance shaft. However, the Kawasaki KZ400, introduced in 1974, featured a 360° crankshaft and a balance shaft.

In addition to reducing vibration (absent a balance shaft), the 180° crankshaft engine suffers fewer pumping losses, as displacement in the crankcase stays roughly constant. However, a 180° engine requires a separate ignition system, points or otherwise, for each cylinder. The 360° parallel twins usually have a single ignition system for both cylinders, with a wasted spark on each cylinder's exhaust stroke.

The parallel twin engine configuration is currently used by BMW Motorrad in its F800 series motorcycles. It uses a 360° firing order, which synchronizes combustion torque and inertial torque from the crankshaft, albeit with relatively long intervals between power strokes as compared to modern inline-four motorcycle engines. This configuration produces exceptional torque, but due to the inherent vibration of a parallel twin piston configuration, is limited to 9,000 rpm. BMW's solution to the vibration problem was to install a third "vestigial" conrod to act as a counterbalance. The sound of this engine is sometimes described as "agricultural" (probably due to the parallel twin configuration of tractor engines), but vibrates much less. Peak horsepower in this design is sacrificed for high torque levels; there are no comparable motorcycles in the marketplace at this time. The choice of the parallel twin engine was likely made to produce an engine note similar to the iconic boxer twin which is the signature BMW Motorrad engine - both engines are twins with 360° firing orders.

In two-stroke cycle engines, the crank angle is generally 180° with a working cycle every 180°. Such an engine will produce fewer vibrations. An exception is the Yankee which featured a 360° crankshaft. The Yankee's configuration, which featured separate combustion chambers for the two cylinders, should not be confused with that of a Twingle.

In four-stroke designs, the parallel twin is usually vertical or near vertical. An exception is the racing-only AJS Porcupine, which featured horizontal cylinders.

[Stichill_imp]

Had to go out of town for a week, only two days after I picked up the bike. I had only managed to put on (200) miles before I left home. Just got back late this afternoon and got another (100) miles on it.




The bike is really superb. Comparing it to the CBR250R, you're giving up nothing but that last increment of lightness and agility...and the excitement of the free-revving thumper. What you're adding is more comfort, much more torque, and smooth refinement. I am enjoying the small niceties like the heated grips, gear indicator, emergency flashers, flash-to-pass high beam, and ambient temperature thermometer. The brakes are extremely stout and the "Forget About It" belt drive is simply welcome. I will say that the CBR gauge concept is superior: large tach with digital speedo. The GT has a small tach on the bottom, and then a large analog speedo that goes up way too high...resulting in lack of readability and precision.

One of the greatest features is the ESA. It allows you to change rear rebound damping on-the-fly between Comfort, Normal, and Sport. Works quickly and very much allows you to adapt the bike to the riding conditions. I was on a road that I thought might call for Sport, but the surface was fairly poor so I changed it to Comfort and the bike settled down and became less nervous.

The transmission is really exceptional. It shifts quickly and with a very positive feel and perfect smoothness. There's a definite clunk from Neutral to First when stopped but it doesn't bother me in the least.

The hard bags are awesome. Don't know how I ever lived without them...never going back. The clutch and front brake lever are adjustable but I have not played around with that feature yet.

I ordered the optional LED taillight. It's extremely bright and I feel good enough about its visibility that I may not need to install Hyper-Lites. I also ordered the extended rear mud guard. Looks OK in my opinion and is very practical.

Besides the instruments, so far my only "recommendations for improvement" would be to direct engine heat somewhere other than the rider's inner legs, and to use firmer foam in the seat. I can see a [url=http://www.sargentcycle.com]Sargent seat in my future.

[Xyzzy_imp]

Fun reading WRT engine vibration and stuff: http://www.tonyfoale.com/Articles/Engine...alance.pdf

[Cormanus]

Thanks Popgun and Xyzzy!

Stichill, what can I say? Seems you've made a good choice. Enjoy.

[Stichill_imp]

Cormanus, I only wish it was "and" and not "or"!

I just wanted to stop back in with some impressions to wrap up this thread. It may become a good archive for people in the future thinking of either bike.

[Lord Popgun]

Xyzzy,

Thanks for that link. Its a LOT of reading so I save it to read later.