Cars, etc.

[Bob Zumbrunnen]

I thought the Harley sound was from the firing sequence...don't both cylinders fire at or almost at the same time?

I'm not sure. An educated guess would be "No". It'd be harder to get the shakes out of it if they fired at the same time and it'd take a really massive flywheel to spin them through two compression strokes happening at nearly the same time.

Unless they're using a pretty weird crank (possible, but not likely -- the design of it would probably make it comparatively fragile), I would guess that both connecting rods are on the same journal, which means that the pistons are only about a dozen degrees apart in their positioning, and would further guess that their power strokes are as close to 360 degrees apart as the cylinder angle will allow.

Edit: We're both right but you're more right than I am. They do fire real close to each other.

http://www.howstuffworks.com/question325.htm