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bike engines

06/16/2008 3:30 AM

why some bikes have horizontal engines, and some have vertical engines,

how does it effects the working

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#1

Re: bike engines

06/16/2008 9:35 AM

think center of gravity next time you look at a bike or car.

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#5
In reply to #1

Re: bike engines

06/17/2008 6:14 AM

I believe that you can get too low, on a cycle.

Balance is achieved by keeping the CG inline w/ the vector-sum of forces from tire; if the moment is too short, steering corrections can't produce enough effect to move the polar bike.

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#2

Re: bike engines

06/16/2008 11:33 PM

In the end, the desired result is the same-to move the motorbike efficiently. It is most important that a motorbike has a low centre of gravity, and different makers achieve this in different ways.

Some engine designs reflect a certain "heritage" as well. Look at BMW-the boxer design is still prevalent there. Look at Moto-Guzzi-the inline crank V-twin is still prevalent there. Look at Triumph-the parallel in-line is still prevalent there. Look at Harley-Davidson-the conventional V-twin design is prevalent there.

What does the maker desire for his motorbike to accomplish? What does the rider want? Fast acceleration but a lot of gear change required, or mild acceleration with little gear change required? Quick handling and response, or just lazy and comfortable cruising without any drama? In the end, it is the desire of the rider (end user) that motivates the builder to make the bike just so.

Which design is better? I don't know. Personally I like V-twins and boxers because of their simplicity, but they tend to not be not smooth engines. It is really a matter of personal taste.

Does any particular engine design make a motorbike more stable, and hence, safer? I cannot answer that one, as the type of engine design is a critical piece of the particular motorbike. I've owned all types, and I really do not remember any serious pros and cons with any design, as far as safety and rideability.

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Ing. Robert Forbus

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#3
In reply to #2

Re: bike engines

06/17/2008 5:19 AM

Air cooled engines must also be arranged to cool properly. The cylinders must catch enough cooling air so that the lubricity of the oil film on the cylinder walls isn't compromised and the bore doesn't distort. The cooling problem with the rear cylinders of the early Ariel Square Four comes to mind.

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#4
In reply to #3

Re: bike engines

06/17/2008 6:08 AM

Circumferential finning tends to expand more evenly, & offer better structure than axial finning; seems to work better.

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#6

Re: bike engines

06/17/2008 6:40 AM

The cylinder arrangement is often made in a particular way to suit the method of driving the rear wheel, some use a chain or belt, some use a drive shaft.

Naturally one could design a gearbox to make either engine drive either drive, but in my (very limited) experience, that happens seldom.

But again, what do I know, I am not a biker anymore for about the last 40 years!!!!

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#7
In reply to #6

Re: bike engines

06/17/2008 7:06 AM

Have seen a few 'double right angle' drives; transverse engine to long't'dnal shaft, tocrownwheel @ axle.

Seems more marketing, than engineering!

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#8
In reply to #7

Re: bike engines

06/17/2008 7:39 AM

You're damn right!!!

The power loss must be fairly high as well as wear and tear on the gears and of course (many forget!) the gearbox oil!!!

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#11
In reply to #8

Re: bike engines

06/17/2008 5:32 PM

Then, again...

Knowing the "care" most modern bikers take of their chain; maybe enclosed 'boxes are better.

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#9

Re: bike engines

06/17/2008 8:59 AM

There is a gyroscope effect of verticals and horizontals. The theory being horizontals do not fight the turn as do verticals.

I've never tested this as when I raced motorcycles (motorbikes to Dell) I learned that my guyroscope (me) fought the turns more than the engine configuration. I spent more time on my head than on the seat. I could pass any competitor in the turns ! And a split second later so did my bike.

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#10
In reply to #9

Re: bike engines

06/17/2008 5:28 PM

"There is a gyroscope effect of verticals and horizontals. The theory being horizontals do not fight the turn as do verticals."

believe you are thinking "polar moment" about roll axis, rather than any gyro effect, as the rotating bits are in similar orientation to bike.

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#14
In reply to #10

Re: bike engines

06/18/2008 5:50 AM

I do believe that the effects in question that he may have wanted to talk about are "Torque" effects.

I have heard over the years that Bikes with a drive shaft (without a chain), do show some side to side torque effects, especially those with relatively powerful engines.

I have never driven a drive shaft bike, so really I cannot comment!!

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#15
In reply to #14

Re: bike engines

06/18/2008 6:00 AM

When the term 'horizontal' is used alone i picture a piston(s) recip fore/aft; Aermacci, Honda 50, AJS "Porcupine" come to mind

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#12

Re: bike engines

06/17/2008 10:26 PM

1. Lowers the C.G. considerably.

2. Boxer types - far less vibration, (some torque reation)

- better air cooling - easier maintenance

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#13
In reply to #12

Re: bike engines

06/18/2008 5:27 AM

Is 'low CG' really desireable in a cycle?

There is no overturning moment, as in a 4 wheeled vehicle; we lean in, instead.

Try the age old trick of balancing an upright broom in your hand, both with the head up (high CG), & with it down (low CG). Which is the easier task?

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#16
In reply to #13

Re: bike engines

09/23/2008 10:52 PM

Low cg is desirable in a sport bike because it lowers the polar moment in roll. The bike must roll around an axis from the front tire contact patch to the rear tire contact patch (unless the front wheel is airborne). Notice how Buell sport bikes place the muffler under the bike between the wheels to reduce polar moment of inertia. In a cruiser, the higher cg slows the reactions and allows lazier steering inputs (broomstick head up). The smaller the polar moment, the faster the bike can be leaned from scraping the right peg to scraping the left peg.

And yes Andy, engines with the shaft running fore-aft cause the bike to roll in reaction to throttle inputs. This was quite a shock to me the first time I rode a BMW Boxer twin (R1150 RT) and blipped the throttle to downshift. Conservation of momentum kicked in and caused the bike to roll (right I think) as the engine revs came up. My old Honda Nighthawk didn't do that because the crankshaft was arranged left-to-right. Both were shaft drive.

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Users who posted comments:

Andy Germany (3); Anonymous Poster (2); bubbapebi (1); Ing. Robert Forbus (1); PetroPower (1); sidevalveguru (7); vicini (1)

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