Video: A Primer on Crossplane Crankshafts

02/04/2013 @ 1:31 pm, by Jensen Beeler18 COMMENTS


Reading through the comments on the Attack Kawasaki CRT bike and its new crossplane crank, it is clear that the concept of what makes an engine have a crossplane configuration, like the one found in the current Yamaha YZF-R1, is still a bit of an enigma for some motorcyclists.

Referring to the way a crankshaft is built, with the four crank pinks at 90° from each other, an inline-four engine with a crossplane configuration fires its four pistons in a different order, and with different intervals between ignitions, than a normal engine with 180° pin positions.

A subject we’ll broach in greater detail at a later time, we thought this video from Yamaha would at least highlight some of the major differences and reasons for using a crossplane crank in a sport bike motor. Enjoy it after the jump.

Source: Yamaha EU

  • JohnEE

    I’m in the group that wanted to know more after the Kawi crt article. Thank you Jensen! Knowing is half the battle!

  • We’ve got a new column in the works that I think you’ll really enjoy John. ;)

  • motobell

    Thanks Jensen! for your upcoming column can you answer the following:

    1. It seems obvious when explained this way – but why has no one done this till recently – pure engineering challenge or other reasons (cons to this approach) – what is holding mass adoption across models and manufacturers
    2. Can you compare the engine characteristics of I4flat & crossplane to Twins (Ducatis), V4s(aprillia)
    3. What kind of bikes will best benefit – only sport or tour /street as well?

  • The first one is easy, this is not the first time a crossplane crank has been used. I saw Michael Czysz tweeting earlier about how the MotoCzysz C1 used a crossplane, and of course GP bikes in the two-stroke era played with crossplane configurations.

  • Paulo

    This is actually turning into an adult discussion………..and I like it! I too am interested in the answers to these questions as well, why only Yamaha, what are the cons? From a purely esthetic point of view………..the R1 sounds AWESOME!!!!!

  • John O

    I’m sorry, but after watching that video “explanation”, I’m convinced the official line of why cross plane is better… is just so much BS.

    At the end of the day we want our bikes’ motors to produce tractable power delivery.

    If it’s a continuous series of pulses, then the rear wheel will constantly be hooking up and breaking free with every power pulse.

    If the power comes in a shorter series of pulses, the motor has a chance to “overpower” the rear wheel but then has a longer period of time to hook up and regain traction.

    Until someone can present me with a non-bs filled video that doesn’t talk about “shifting the paradigm” I’m going to stick with my theory.

  • BBQdog

    This video was necessary Jensen, also for me, thanks.

  • sburns2421

    What the crossplane does (I assume Attack is similar to Yamaha) is allow the cylinder pairs to transfer their kinetic energy to one another (i.e. as one piston/rod assembly is slowing down, its neighbor is speeding up.)

    A typical inline four has all reciprocating mass at the same velocity for a given crank angle. Pistons reach max velocity at the same time and reach zero vertical velocity at the same time.

    The downside of the crossplane crank is a bit more difficult to manufacture (and maybe a bit heavier), and the engine should require a balance shaft or some other clever way of balancing the engine.

  • Shawn

    @John O

    What that video just explained was that the crossplane crank reduces the magnitude of the “power pulse” and increasing it’s frequency, smoothing the rotational velocity of the crank and creating a much smoother torque delivery. Which increases tractability. Just like they claim.

    Your idea of the flatplane crank allowing the tires to hook up better (at a rate 500 pulses/s for the flatplane at 15000 rpm) isn’t practical and can be tested by looking at an engine dyno chart.

  • Bruce J.

    sburns2421 explanation was better than the video.

  • CTK

    John O.,

    You are forgetting, those power pulses are happening hundreds of times a second. The smoother the power delivery, the more “smeared” the power, which enables a slide to be propagated for longer once its initiated. With the herky jerky power delivery of a crossplane crank, a slide is less likely to happen, as its harder to propagate.

    I am not sold on crossplanes though. As orgasmic as the R1 sounds, it’s significantly heavier and less powerful than its competition. Still really not of concern to me, as its still a 150WHP bike, but that speaks to the inferiority of the technology in the real world. The hideous face of it ices the cake.

    Kawi’s CRT bike is NOT a crossplane though. From its sound I am more inclined to believe it is a big bang in the vein of the 2005 ZX-RR. It sounds like a raspy parallel twin… which also makes sense, given the connection to its long standing line of Twinjas (250R, 300R, 500R, 650R etc). Def not a glamorous MotoGP sound, but if it doesn’t shake itself apart at 15000 RPM it should make for similar power with better delievery. I’m looking forward to it.

  • Paulo

    Hey John Oh……

    You don’t have to be sold on the R1; as you suggest “speaks to the inferiority of the technology in the real world”. My counter point. Why are we then talking about it? If you review Motorcycle USA article found here—> your points are not clearly valid. 1st, If you take the high and low weight of the bikes they compare the R1 is 11lbs within the mean not considering the Ducati. Factoring in the Ducati the R1 is within 15lbs of the average weight. I’m sure you’ll agree the MV Augusta is a beautiful bike (to die for some would say)…..well it’s 475lbs……11bls heavier then an R1. Also using this article if you look at superpole numbers the R1 is under 2seconds from the best lap time! Maybe it’s me but are you trying to impose an opinion or fact? I’m sorry man but talk to Josh Hayes and Josh Herrin about what goes around faster around a track in the AMA circuit. You may not like the bike or even the crossplane technology however your opinion doesn’t have merit.

  • jfc1

    …it fires 1-3-2-4 just like my car. What’s to it?

  • @Bruce J. +1

    It’s key to know that adjacent pairs’ pins are 90 from one another, not each consecutive pin.

    The music in the video comes across as improv jazz, i.e. all over the place, which is opposite to a “linear” explanation

  • Cpt.Slow

    This still needs explaining ?

  • John O

    The explanations offered here (smoother torque application, less likely to enter a slide, easier to control a slide) make far more sense than the marketing mumbo jumbo offered by that video.

    If it didn’t work… Why is MotoGP (or old-school 500 GP) using variants of this tech?

    More succinctly: I’m not claiming the crossplane doesn’t work. I’m just claiming Yamaha’s overly wordy explanation for how it works… doesn’t work ;)

  • Zato

    Kevin Ash’s explanation of this subject was very good I thought –

    Basically the crossplane configuration smooths out the inertial force of the crankshaft. Interestingly Kevin disputed the common explanation that it’s the firing order of big bang engines that produces better traction (as in each power ‘pulse’ being spaced further apart, giving the tire time to regain traction).

    Smoothing out the inertial torque of the crankshaft does smooth out power delivery however, so it could be said that the big bang firing order is more of a side effect to the actual aim of using a crossplane crank.

  • Forget the Crossplane… some here need to be put in the cross-hairs… :)

    It’s a great thing, for sound, if you have ridden one you’ll admit to the smoothness that the bike revs… almost rotary like… it feels wierd at first, but it’s very alluring in how it works. Faster, no, but 150 hp is cool for me.

    I think Yamaha said it best recently… out side of racing where you capatlize on strengths and cut the weaknesses; in the manufactured bike you have a little heavier motor and of course due to design, you have a much wider motor.
    For the common candidate… US; we would be fine and if you like it, you like it. I do agree with the ugly face syndrom, but the new one is much better IMHO.

    Ride one and take it for what it is… there is only one choice and it’s allowed Yamaha to compete pretty well in Moto GP and AMA and WSB and BSB…