Details: 2009 Yamaha R1 crossplane crankshaft

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crossplane_crankshaft.jpgAcknowledging that, deep down, every motorcycle fan has the intellect of a seven-year-old, Yamaha has come up with a nifty song to help us understand how the 2009 Yamaha R1‘s crossplane crankshaft engine works. The secret’s in the firing order. Whereas a traditional inline-four goes: one, two, three, four, combusting on each number, the crossplane crankshaft engine goes: one, two, three, one, two, one, one, two, combusting on the ones. Try singing it with a drum set keeping a beat, or just watch this video.
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Basically that means two cylinders fire with the normal degree of
separation before two cylinders fire one after the other, creating a
long bang. It’s this long bang that gives the engine its unique
character, sending large pulse of torque to the rear wheel, then giving
the tire plenty of time to regain traction before the next one comes
around.

This differs from a big bang engine in that it doesn’t fire two-by-two.
That arrangement creates huge levels of vibration (also a problem on a
long bang engine, they’ve fixed it with a counter-rotating balancer)
that would impact engine longevity in a production application.

This arrangement is given the confusing “crossplane crankshaft” moniker
due to the lobes for the outer cylinders being pointed in the same direction,
then the inner cylinder lobes being horizontally opposed, 90 degrees of rotation from the outers.

This was all a lot simpler than we thought it was, but we feel
strangely satisfied, in an elementary school kind of way, for having
learned something new thanks to mnemonics.

Thanks for the tip, Sean.

  • Charles

    Huh, makes sense I guess.

    I would assume then that the R1 won’t have the smooth and balanced idle that I normally associate with an inline-4?

    • Marty T

      Why would you ASSume that?

  • http://hellforleathermagazine.com Wes

    You can hear it run in the video. I think it’ll idle fairly smoothly, maybe a bit like a cross between a v-twin and an inline-four. Basically, it’s delivering the out-of-corner drive of a v-twin with four-cylinder power.

  • Kevin White

    Why is this better than having two cylinders fire at the same time? Or having three fire at the same time? Or all four in quick succession? Or all four at the same time?

  • Kevin White

    Also, this is interesting. Can anyone describe the difference between the VF Interceptors and the VFRs? I had a VF700 with the droney engine note. The VFRs have the more soulful engine note. How does that relate to the firing order/crankshaft?

  • SDMike

    The VF and ST series engines (along with the RC30 and RC45) use a 360 degree crank. The VFR series uses a 180 degree crank. This refers to the spacing between adjacent cylinders. In a 360, the rear bank rises and falls together. In a 180, one is at the top while the other is at the bottom. Note that this doesn’t mean that they fire together in a 360. For reference, a VFR firing sequence is 1-3-2-4, timed at 180-270-180-90.

  • Kevin White

    Thanks. I suppose the 360 degree crank had some type of advantage in the power delivery, but the 180 won out for road use (and not just because of the engine note that is considered more appealing).

    This firing order stuff would probably be easier to understand if they were all two strokes…

  • http://ridethetorquecurve.blogspot.com hoyt

    Kevin – to answer your question about why is it better than 2 cylinders firing at the same time… I believe it is due to longevity of the engine and less vibration.

    Hopefully this Yamaha technology will have more of a lasting impact than their 5-valve head

  • Doug

    As I understood it, the RC30, RC45, NC30 and NC35 all used the so called Big Bang type ignition. This was for better drive out of the corners. It was 360 deg but I’m not sure if the VF and ST were too?

  • http://www.biotivia.com/ James

    This differs from a big bang engine in that it doesn’t fire two-by-two. That arrangement creates huge levels of vibration (also a problem on a long bang engine, they’ve fixed it with a counter-rotating balancer) that would impact engine longevity in a production application.

  • MikeH

    I don’t get this, I thought rotational inertia of the crank tended to keep angular speed constant. If the mass of the crank remains the same, why does the momentum change?. I would have thought that irregular firing would exacerbate the change in rotational speed, not improve it. How does a rear tyre behave better with three close power impulses followed by a gap, rather than four smaller, even spaced ones. Seems counter intuitive to me.

  • Matti

    The rotational inertia thing is mostly marketing bullshit. However, the crossplane crankshaft should have less of the high-frequency vibration associated with inline-4′s because something you can see on the video. In conventional ‘flat plane’ crankshaft all the pistons slow down at the same time twice per a rotation shifting their kinetic energy to the crankshaft accelerating it. When they start moving again, they soak up the kinetic energy of the crank. This is shown as the sinusoidal torque seen at the crankshaft but it’s frequency is so high that it is not felt at the rear wheel anymore.
    In the crossplane version the sum of the kinetic energy of the pistons is almost constant and so the inertia of the pistons exerts little torque to the crank. I think this should be felt as smoother running engine which means less vibration.
    The benefit of the (inline-4) flat plane crank is that the momentum of the two middle pistons compensate the opposite momentum of the side pistons, which doesn’t happen with the flat plane crankshaft. This requires a balance shaft to be used with the yamaha crankshaft.
    The uneven firing order seems to produce a nicer exhaust note also, which I think is the other benefit of this rather exotic crankshaft design.

  • MikeH

    So the advantage of the crossplane crank is that the sum of all piston inertia is close to zero, the irregular,”long bang” firing sequence is an unfortunate by -product, it produces vibration that requires an additional balancer shaft to iron out.

  • Wallie du Toit

    Even the works Yamaha rider Ben Spies (Elbowz) refers to big bang all the time after the Kyalami test session. “Long Bang” is definitely technically correct.

  • touristguy87

    “Why is this better than having two cylinders fire at the same time? Or having three fire at the same time? Or all four in quick succession? Or all four at the same time?”

    They just explained it to you in the video. IMO 90% of that video was hokey, except for maybe getting to watch the R1 run around and the exploded view of the bike. The meat of it is the simple explanation of the inertial nonuniformity with rotation of the crank-piston combination. Essentially the engine produces power in uneven pulses from ignition which occurs only during the ignition stroke (of a 4-stroke engine). So sure, one approach would be to have different pistons fire in succession, which I guess is the traditional approach. So ok, which pistons do you have fire in which order? 1-2-3-4, 1-3-2-4, 1-4-2-3…1&4 than 2&3? All valid approaches to the question, ignoring other factors like…harmonics (resulting from the power-pulses of the ignition stroke) and variations in the angular velocity (and by extension the angular momentum) of the crankshaft. The crossplane crank attempts to smooth-out variations in the latter by putting the pistons 90deg out of phase, first and foremost, in an attempt to keep the angular velocity constant. The rest just comes out of getting the cylinders to fire with the minimum vibration as a result.

    The big point that comes out of this to me is that vibration is the big problem. Frankly I don’t see a difference in control or power-smoothness when the engine is spinning at 5000rpm, where an 18″ wheel at 60mph is turning about 10rpm. All the problems with “inertial fluctuation” is lost in the gearing (obviously, or we couldn’t ride much less accelerate “traditional” bikes through corners). If it was that big of a difference I’m sure that someone would have pointed it out long ago and that such a design would be the norm. But obviously keeping the engines’ angular momentum constant means that it cannot accelerate. You want to smooth-out harmonics, increase the angular momentum of the crankshaft, but that will make it much harder to accelerate. The fundamental problem is to reduce the inherent vibration of the engine and if there is any benefit in this design, that’s where it is. That will lead to lighter, faster & more robust bikes that are more fun to ride.

    Though not necessarily “cheaper” :)

  • touristguy87

    “Frankly I don’t see a difference in control or power-smoothness when the engine is spinning at 5000rpm, where an 18″ wheel at 60mph is turning about 10rpm”

    er, 10rps :)

  • touristguy87

    Really reading this raises questions about scope as one begins to wonder why not ABS, why not V4′s or even V8s…why not bring in all sorts of technologies to eliminate vibration and to make the bike easier to ride in and out of corners? Why just play with the crank?

    Why not variable-lift/variable timing cams?

    Take us back to the logic of going from an 18″ front to a 16″ on the FJ1100 and then to a 17″ on the FJ1200 and the original YZF-1000…why not just restrict the throttle when the bike is leaned over? There are all kinds of games that Yamaha could play here, playing with the crank is trivial unless they can drop the weight of the bike by 10% or more as a result, like Honda has done with the CBR, or boost power by 10%, like Kawasaki has done.

  • http://DANY Dupuys Daniel

    Yamaha has made a copy of a V4 without the risqs of a completely new design (see Suzuki results in motoGP race).The crossplane timing fire is 270/180/90/180;the Honda VFR one and DUCATI is:180/270/180/90°(it’s the same according where is the Nb 1 ref.cylinder).This to allow longer times between firings(amount of torque) to the rear tire when used at the limits in motoGp race and to increase the grip. This was used in the past with the 2 strokes BIG BANG engines.
    It’s probably a good solution regarding the Yamaha results!
    DANY

  • http://robbyshiddenthoughts.sinau.org/ Graham Tomory

    Which is an excellent piece, usually good to understand a lot more about aviation.

  • fastfitter

    “every motorcycle fan has the intellect of a seven-year-old”

    “a traditional inline-four goes: one, two, three, four”

    Looks like ‘jounalists’ aren’t much better :-))