One of the members here has a nice avatar which is a .gif animation of the V-Twin engine. I have copied that animation and decomposed it into its individual frames.

Here is the animation...



Ok, so here is one of the frames. This frame shows that when the front cylinder is at the bottom of the intake stroke, the rear cylinder is at the bottom of its power stroke. Is that the way it actually is? I would not have thought that both pistons would be at the bottom of the cylinder at the same time. They must be connected to the flywheel at the same point???



I would have thought that when the piston of one cylinder was at TDC the piston in the other cylinder would be at or near BDC. But I really have no idea. This is new territory for me.

Here is a link to a simple description of how back and forth motion is converted into circular motion using a crank arm, connecting rod and flywheel.
https://mechanicalgifs.com/models/piston-and-flywheel/

 

yes this is accurate. The pistons aren't "One hundred and eighty off" for lack of a better term. If you look at the animation, both pistons are on the same crankpin, the piston fires, and the inertia spins the crank around untill the other piston hits TDC compression, and then it fires. I am sure someone else can explain it better...it has something to do with the degree of offset for the pistons to fire the way you describle.

 

With the two pistons sharing the same crank pin, they won't like up like that. I believe in order to line up like you stated, it would have to be staggered in 90 degree multiples. Of course that number is after you've subtracted (or added) the 45 degrees for the cylinder. If I'm not mistaken, the mid 80's Honda V-twins did it that way.

 

And then there's that dual fire thing.

 

But we still haven't really figured out this diagram yet......

 

I had a military instructor that used to say "don't ask why just know that this is the answer:...

 

Why is the sky blue, Bob?

 

I am noticing the arrows in the images. The arrows are showing the direction of motion.

I was wrong in my first post. The front cyclinder is not at BDC but the rear cylinder is at BDC.. The second frame shows the front cylinder is still going down and the rear cylinder starts going up. Does this mean that the rear cylinder ALWAYS reaches BDC before the front cylinder? (in this configuration)



As I think about this, they cannot both be at BDC (or TDC) at the same time because of the angle.

 

Whenever I get overwhelmed with the mechanical function of anything I always resort to this video and it always clears things up. Check it out and see what I mean.

 

Dual fire doesn't matter on this kind of engine. It's easier to have both fire at the same time than to do something like a distributor, like cars do. The firing only matters on the one cylinder that is ready for it at the time. I don't know if they've made it a selective fire on later models though.