Categories: Ask MO Anything

Ask MO Anything: Why are Yamaha the only ones to use a “Crossplane” crankshaft?


Dear Cranke,

Suzuki was hoping you’d ask. Here’s what they had to say in introducing the all-new GSX-R1000 last week, which uses the same 180-degree, or flat crank, it always has. Our lead photo shows the new GSX-R engine on the left and the outgoing one on the right; note that the baby bump on front of the old engine, where its small balance shaft used to live, is no more on the new engine.

Nearly all inline Fours use a flat crankshaft like this one (which doesn’t belong to the new GSX-R). Two pistons up + two pistons down = perfect primary balance.

“Suzuki engineers carefully considered using non-conventional, uneven-firing-order crankshaft phasing versus the GSX-R’s traditional even-firing-order crankshaft phasing.

“The theoretical advantages of uneven firing order can apply in MotoGP racing, where engine output exceeds 230 horsepower and the biggest obstacle to turning good lap times is cornering traction and the rider’s ability to feel how well the rear tire is hooked up at any given throttle opening. But there are very real inherent engineering challenges that must be overcome with an uneven firing order. It’s more difficult to produce strong power and torque with an uneven firing order, especially at low rpm and in the midrange. Vibration is increased, requiring much thicker and heavier crankcases and a counterbalancing shaft, and associated mechanical losses contribute to overheating.

Yamaha’s Crossplane crank needs to spin this large balance shaft (part #14 on BikeBandit’s fiche) to quell its vibes; Suzuki’s new GSX-R1000 does away with the small balance shaft it used last year, joining other balance-shaft-free inline Fours like the BMW S1000RR, Honda CBR1000RR and others.

“The big question Suzuki engineers faced was whether or not, for a production motorcycle, the theoretical advantages of an uneven firing order design outweighed the inherent complications. Including the fact that solving the problem of making strong power with an uneven firing order while controlling vibration, heat and weight gain would make the motorcycle more expensive, significantly increasing the retail price.

“With testing, the engineers found that they could enhance traction and feel with a superb chassis design and effective electronics. And they decided that the even-firing-order, screamer engine sounded better, too.”

Ouch.

There you have it. We love the texture of the R1 big-bang engine and how it sounds, but time will tell if its added complexity eventually might go the way of the five-valve head.


Direct your motorcycle-related questions to AskMoAnything@motorcycle.com, though some say we’re better at non-motorcycle-related ones…

John Burns

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