In a parallel twin that has conventional crank spacing, there is a period of time where both pistons come to a stop at the same time, at top dead center and also bottom dead center, and that has an affect on crank rotation. By the law of conservation of momentum, when the pistons stop, their momentum cannot disappear. What happens when the pistons stop is that their momentum adds to the crank’s rotation speed. Then, as the pistons begin to accelerate again, the crank gives up the stored momentum back to the pistons and is hence slowed down. This constant interchange of momentum between the pistons and the crank shows up as a continuous speed up and slow down on the crankshaft that is a form of torque “noise”.

By quartering the engine as Yamaha have done, when one piston is stopped, the other is near its full speed. In this way, the pistons exchange momentum with each other instead of with the crank shaft. The crank shaft become free of this noise in its output so that the rider feels a more pure sensation of the engine’s true torque characteristic that comes about from combustion.

So it may sound like marketing speak, but there is a factual basis behind what they are saying.

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Now let’s consider the FACTS. The FACT is that Andy1300 wrote:

“I say Barber is just full of himself …”

Now you say that Andy1300 is expressing a sentiment that has as much legitimacy as anything that I have expressed. That’s just plain crap. By what stretch of the imagination does a comment directed at me personally, that denigrates me in an overt, direct, express manner, qualify as a legitimate comment? This is absurd on face value. You say that I denigrate other people. I do not. Andy1300 did however denigrate me in an overt, express manner, yet you overlook that and say that he was expressing a legitimate sentiment. Well, he did in fact express a legitimate sentiment, and if that was all he had done, then I would not have responded to what he wrote, and you would have had no reason to write what you wrote. But the facts are different, and they are right there in black and white. No one should be allowed to say something of the sort that he said about me. You should be ashamed for not saying that to him, and instead chastising me merely for defending myself. I will always defend myself whenever another person attacks me personally without my having given them reason to do so, and that is exactly what happened here.

I did at first merely make the point about the discrepancy on Yamaha’s web site. My reason at first was only because there were comments made here that did come across as technically correct to me, and I thought it would helpful to illuminate the thought process by which it is easily possible to deduce what the 90/270 crank does and does not imply for the timing intervals. I thought that rather than repeat whatever nonsense I picked up somewhere else in the manner that is common, that I would illuminate the matter, not saying that it is this or that, but rather explain how, merely by studying the situation, you can arrive at the true implication that this particular crank has for the timing interval. That was what I did, at first. But then when someone else comes along and writes something along the lines of, “I think Barber is just full of himself,” then I am certainly going to respond. I will also note that THE PEOPLE WHO ARE PRONE TO DO THAT SORT OF THING RARELY EVER USE THEIR REAL NAMES. I am one of the very few people who dares to use their real name, possibly the only one. I do that intentionally, because I TREAT PEOPLE EXACTLY THE SAME WAY THAT I WOULD IF I WERE SITTING DOWN AT A TABLE AND HAVING THE CONVERSATION PERSON TO PERSON. This is in stark contrast with what most people do. The comment that Andy1300, whoever in hades he happens to be, is sort of borderline. I can see where someone would make a comment of that sort in jest with a buddy. But I do not know Andy1300, and I have no reason to believe that the comment was in any way meant to be in jest. But if I did not him personally, and he made a comment of that sort while we were sitting and maybe drinking a beer or two, I would have responded exactly the way that I responded. I think my response was entirely appropriate. If you think differently, it probably has a whole lot to do with the fact that you are not the person to whom the comment was directed. He did not say, “I think that Edge is full of himself.”

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And you haven’t said anything remotely intelligent. For you to have said anything intelligent, you would have to have shown why something I said is incorrect. Nothing I said is at all incorrect. You don’t have to have any special knowledge of any sort to figure out that with the sort of crank that this bike uses, two distinct firing interval sequences are possible. If you simply sit and think it through, you will come to the realization that it can be either 270-450 (summing to 720), or else 90-630 (likewise summing to 720). This isn’t something that is especially difficult to figure out, and it is manifest that in one case the intervals are in the ratio of 3:5, and that in the other case they are in the ratio of 1:7. Anyone who stops and thinks it through should readily come to this same conclusion. Now, the only question is what Yamaha has claimed, and for that, all you need do is go to their web site, just like I did, and study it for a few minutes. I did not say anything that anyone who is willing to take a little time and look into it would not conclude just the same as I did. It is right there, for anyone who thinks that in circumstances where truth is at issue, that truth matters. You evidently believe that even though truth is at issue here, that truth does not matter.

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