The one thing that's considered a significant problem in motorcycles is also Harley-Davidson's greatest strength: vibrations. It's taboo in modern motorcycles, but when it comes to the American bikemaker, this trait becomes a character deeply ingrained in its DNA. Harley-Davidson motorcycles go beyond mere vibrations. They shake. It's a special kind of shake that Harley purists love. They are so important that even Harley's electric LiveWire has it! In fact, when Harley-Davidson made a motorcycle called the V-Rod with an all-new liquid-cooled engine, Harlistas hated it for its lack of vibration. So what makes the Harley Shake special?
It has a lot to do with Harley-Davidson's V-twin engine design. There are two primary reasons behind their vibrations. It is the engine's traditional 45-degree bank angle between the two cylinders and its uneven firing order. It is this uncharacteristic motor which also gives Harley-Davidson its signature 'potato-potato' exhaust note. So the next time you swing a leg over an old-school Harley, think about why it shakes the way it does.
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When it comes to V-twins, 90-degree configurations are preferred for their relative smoothness. Ducati and Suzuki used them with varying degrees of success. But not Harley-Davidson. For most of its storied history, Harley-Davidson motorcycles have used a 45-degree bank angle. Why? Because it is a more compact engine, with the two cylinder banks sitting closer to each other. A compact engine is easier to package, especially in a motorcycle where space comes at a premium. A 45-degree V-twin is inherently imbalanced, which causes vibrations. Adding to this is Harley's firing order, which also gives it its signature 'potato-potato' exhaust note.
In a traditional twin-cylinder engine, the connecting rods (connected to a piston at one end) sit on two separate crank pins of the crankshaft at a space of 180 degrees or at opposing ends. This allows one of the two pistons to fire every revolution of the crankshaft (360 degrees), which balances out the engine. In the case of Harley's 45-degree V-twins, both connecting rods sit on the same crank pin. Also, the firing order is set at a 45-degree offset. Which means, instead of firing at 360-degree intervals, two pistons fire at 315-degree intervals. Post that, there is a long, 405-degree gap before the next piston fires. That means the firing sequence is: Piston 1 fire – piston 2 fire at 305 degrees – 405 degree gap – piston 1 fire – cycle repeat.
This gives Harley-Davidson its signature uneven firing order. The combination of two connecting rods, one crank pin, and an uneven firing order results in an imbalanced engine, causing heavy vibrations. Many Harley-Davidson motorcycles came with the engines solidly mounted to the frame, leading to engine vibrations being transferred to the rider. As much as Harley riders love their thump, some riders seek ways to reduce motorcycle vibrations.
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While Harley-Davidson went with the flow, creating inherently imbalanced engines on public demand, it did take steps to curb excessive vibrations. This was done by adding rubber mounts and counterbalancers. A counterbalancer is a weight that rotates on a shaft in the opposite direction to the engine's rotation. This opposite movement created inertial forces that cancel out vibrations produced by the engine.
Harley-Davidson did try new engines, like the unsuccessful liquid-cooled Revolution 60-degree V-twin in the 2002 VRSC V-Rod. It now uses a modern liquid-cooled Revolution Max 60-degree V-twin seen in current Harley-Davidson models like the Pan-America 1250, Nightster, and Sportster S.
In 2016, Harley-Davidson showcased its new Milwaukee-Eight engine, which went on to power almost its entire lineup. The Milwaukee-Eight is so good, it'll make you lose your pants. The V-twin features a single, large counter balancer that Harley claims cancels out 75 percent of the engine's vibrations. Of course, it still retains that characteristic 45-degree bank angle and 'potato-potato' exhaust note, along with a degree of vibration that's enough to keep loyal customers in the fold, while not excessive enough to dissuade newer buyers.
