bike engines

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

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.

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

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!!!!

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

Seems more marketing, than engineering!

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!!!

Then, again...

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

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.

"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.

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!!

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

1. Lowers the C.G. considerably.

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

- better air cooling - easier maintenance

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?

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.