(03-14-2014, 07:02 PM)Flynrider_imp Wrote: I was cruising down the freeway last Sunday when I noticed I hadn't bothered to shift into 5th (as usual). I was turning 5K rpm in 4th and that feels normal to me, since that's what the CB750 does in 5th at 75 mph. When I shifted into 5th and the rpm dropped to 4200, I noticed that I actually felt more vibes in the bars than I had at 5K. I thought it was a bit strange, so I shifted back and forth and it definitely seemed shakier at the lower rpm. Maybe that's why my brain so often forgets to shift up from 4th gear.

I used to own a lot of twins with 360 cranks, so vibration was just a normal part of motorcycling. When I took my first ride on an I-4 bike ( a Kaw Z-1) I was stunned. I never knew a motorcycle could be so smooth. In fact after I started it, I had to double check the tach to verify that the engine was running. I don't think I'll ever go back.

BTW, the shakiest bike I've ever ridden was a Yammie XS650 twin that was converted to a "twingle". The cam was modified so that both cylinders would fire simultaneously. Interesting bike, but it couldn't be kick started by anyone under 250 lbs. and the electric start would only work if you hooked a car battery to it. The guy that modified it didn't think of adding a compression release

(03-15-2014, 01:21 AM)Scoobynut_imp Wrote:

(03-14-2014, 07:02 PM)Flynrider_imp Wrote: I was cruising down the freeway last Sunday when I noticed I hadn't bothered to shift into 5th (as usual). I was turning 5K rpm in 4th and that feels normal to me, since that's what the CB750 does in 5th at 75 mph. When I shifted into 5th and the rpm dropped to 4200, I noticed that I actually felt more vibes in the bars than I had at 5K. I thought it was a bit strange, so I shifted back and forth and it definitely seemed shakier at the lower rpm. Maybe that's why my brain so often forgets to shift up from 4th gear.

I used to own a lot of twins with 360 cranks, so vibration was just a normal part of motorcycling. When I took my first ride on an I-4 bike ( a Kaw Z-1) I was stunned. I never knew a motorcycle could be so smooth. In fact after I started it, I had to double check the tach to verify that the engine was running. I don't think I'll ever go back.

BTW, the shakiest bike I've ever ridden was a Yammie XS650 twin that was converted to a "twingle". The cam was modified so that both cylinders would fire simultaneously. Interesting bike, but it couldn't be kick started by anyone under 250 lbs. and the electric start would only work if you hooked a car battery to it. The guy that modified it didn't think of adding a compression release

That's an interesting observation which I concur with. I've found when I rev my bike beyond 5k rpm up toward 7.5k rpm the motor definitely passes out of the 'vibe' range and smooths out again at those higher rpms. You might call me crazy, but I think a freer-breathing exhaust helps a motor run smoother at higher rpms. I have a staintune on my bike, but then again I didn't really rev the bike high when it had the stock exhaust. The reason I say this is that I had a Subaru that got very vibey above 5k with stock exhaust, but once I installed a free-flowing exhaust it was smooth as glass all the way to redline, as if the stock exhaust choked the motor up and caused vibes at higher rpms. In any case, that was my experience with that car.

(03-15-2014, 02:09 PM)Red Mist_imp Wrote:

(03-15-2014, 01:21 AM)Scoobynut_imp Wrote:

(03-14-2014, 07:02 PM)Flynrider_imp Wrote: I was cruising down the freeway last Sunday when I noticed I hadn't bothered to shift into 5th (as usual). I was turning 5K rpm in 4th and that feels normal to me, since that's what the CB750 does in 5th at 75 mph. When I shifted into 5th and the rpm dropped to 4200, I noticed that I actually felt more vibes in the bars than I had at 5K. I thought it was a bit strange, so I shifted back and forth and it definitely seemed shakier at the lower rpm. Maybe that's why my brain so often forgets to shift up from 4th gear.

I used to own a lot of twins with 360 cranks, so vibration was just a normal part of motorcycling. When I took my first ride on an I-4 bike ( a Kaw Z-1) I was stunned. I never knew a motorcycle could be so smooth. In fact after I started it, I had to double check the tach to verify that the engine was running. I don't think I'll ever go back.

BTW, the shakiest bike I've ever ridden was a Yammie XS650 twin that was converted to a "twingle". The cam was modified so that both cylinders would fire simultaneously. Interesting bike, but it couldn't be kick started by anyone under 250 lbs. and the electric start would only work if you hooked a car battery to it. The guy that modified it didn't think of adding a compression release

That's an interesting observation which I concur with. I've found when I rev my bike beyond 5k rpm up toward 7.5k rpm the motor definitely passes out of the 'vibe' range and smooths out again at those higher rpms. You might call me crazy, but I think a freer-breathing exhaust helps a motor run smoother at higher rpms. I have a staintune on my bike, but then again I didn't really rev the bike high when it had the stock exhaust. The reason I say this is that I had a Subaru that got very vibey above 5k with stock exhaust, but once I installed a free-flowing exhaust it was smooth as glass all the way to redline, as if the stock exhaust choked the motor up and caused vibes at higher rpms. In any case, that was my experience with that car.

Exhaust design absolutely can contribute to perceptible vibration. That's what an exhaust muffler is, it resonates in sympathetic frequency (sound cancellation) as well as changes the direction of the sound the engine makes. Some bikes, first generation FZ1, for example, actually have a weight added to the pipe mount to absorb vibes.

You put on a straight pipe and the shakes will go away cuz the gases have a clear path, unobstructed.

(02-12-2014, 07:02 AM)calamarichris_imp Wrote:

(02-11-2014, 09:19 PM)Cormanus_imp Wrote: It's a lovely thing. Thanks for posting that photo, Chris. You know f*$k all about beer.

Haha--I might surprise you Pal. I raced bicycles in Limburg and lived there for 3 years--down in the little geographical Dutch nutsack dangling between Germany (West Germany back then), and Belgium. Was just about 70km from Cologne/Koln, and I was a regular at all the best Kolsch breweries. After visiting me, my father started brewing his own microbrews and won many awards; (this was back in the dark days of Coors & Budweiser, before microbrews caught on in the US.)
And now I live about 4 miles from ground-zero of San Diego's microbrew big bang. I have growlers from 8 of the ~20 different breweries here (though most of them are obsessed with this IPA fad right now, which doesn't make much sense to me in a time of refrigeration and sanitation.)

I was a little tipsy on the pilsner last night, and was just joshing about Aussie beer. Cheers mate! If you ever make it to the upper half of the world, bring your boots & helmet. We've got some terrific breweries here, and even better silly-string roads.

(02-11-2014, 02:15 AM)DAC_imp Wrote: The only disadvantages for an I4 that I know of came from reading Kevin Cameron (Cycle World.) He puts some people to sleep but he did one article comparing I4s to V4s, mainly in racing applications, and since I own a V4 Interceptor I was able to stay awake for that one.

First, an I4 with a 180* crankshaft has a dead inertial moment twice every rotation as the pistons bottom out/top out at the same time. IIRC, this creates a need for beefier counterweights on the crank. Racing engines where the counterweights were lightened up too much resulted in "shuddering" at corner exit as power was applied at lower RPMs. In the V4, when two pistons are at the top/bottom of their stroke, the other two are in the middle of a stroke, resulting in continuing inertia, and the ability to use lighter counterweights.

With the heavier counterweights and a generally longer unit, the crank has much more of a gyroscopic effect, resisting turn in, and making the bike feel heavier. Again, V4s by nature have a narrower crank and produce less such turning resistance.

As Ferret mentions, the engine is wider in an I4 and can create a teeter totter effect compared to an V4, which is more centralized in the bike like a bowling ball.

Another difference between these two isn't an advantage/disadvantage, just a difference. The I4 makes its power fairly evenly with power pulses like x-o-x-o-x-o-x-o. That's a gross oversimplification, I think, but you get the idea. The V4 is more like x-x-o-o-x-x-o-o. That is also an oversimplification. In racing, the V4's gap in power pulses aided corner exit by acting like a kind of traction control as the "rests" helped the tire reconnect in moments of too much throttle while the bike is leaned over. However, in a street riding application, this has little utility.

Finally, there's the sound. An I4 can have that angry-hornet-riding-a-jet-turbine sound while a V4 has a distinctive growl often described as half of a small block Chevy. Both, frankly, are music to my ears.

(12-13-2015, 11:13 AM)thessler3_imp Wrote: I see a lot of mis-truths posted in this article about inline 4 cylinder vibration. Inline fours with 180 degree cranks have very good primary balance and very poor secondary balance. Primary vibration is at crankshaft RPM. Secondary is at twice engine RPM. Most inline fours have balance shafts. The CB1100 and ZX-9 and most other fours have a single balance shaft that turns at twice engine RPM. Some bikes, like the Blackbird have two shafts that turn in opposite directions. In either case, the shafts help, but rotating weights are a compromise when trying to cancel reciprocating motion. Balance shafts were first invented and patented by British engineer Frederick W. Lanchester in 1904. Most 4 cylinder cars have balancer shafts and rubber mounts. Think of it as belt and suspenders. CB1100 does have one rubber mount at rear. Nearly every engine configuration on motorcycles has inherent vibration of some sort. Exceptions are the sixes - CBX and Gold Wing are quite smooth and need no balancer shafts. 90 degree V-twins are smooth in moderate displacements, but have some secondary vibrations. I have a classic Ducati 750GT that is pretty smooth. I am sensitive to vibration in my hands after riding for more than 50 years and I have studied the subject extensively.