The Back Story of Motorcycling’s Greatest Innovation Takes a Wild Turn

Nowadays, the V-twin engine is ubiquitous in the motorcycle world. Powering everything from speedy sport bikes to massive touring machines — and even wedged sideways on some rides — the still-striking dual-cylinder motor is almost inescapable.

However, for those who care about moto history — and innovation — it’s important to remember that was not always the case. 

Harley-Davidson

The V-twin did not truly begin its takeover of the two-wheeled world until around 1907, when William Harley, chief engineer of Harley-Davidson, decided to power up the brand’s early bikes by doubling down on cylinders. 

What may be even lesser-known, however, is that a V-Twin-powered bike H-D actually wanted on the market did not appear until 1911. Here’s what happened in between.

Double trouble

First off, it’s worth noting that Harley was not the first motorcycle brand to employ a V-twin.

When motos began to emerge in the late 1890s, they were little more than bicycles with often clunky engines bolted on. 

But drawing inspiration from Gottlieb Daimler, who built a V-twin for boats and cars in 1889, a smattering of brands began experimenting with V-twins in the early 1900s.

These brands included the UK’s Princeps AutoCar Company and Eclipse Motor & Cycle Co, the USA’s Glenn Curtiss and Germany’s NSU Motorenwerke. 

Meanwhile, a V-twin made by French brand Peugeot powered a UK-made Norton motorcycle to victory at the first Isle of Man TT race in 1907. 

Still, what made the V-twin so legendary and widely adopted was what Harley-Davidson did with it. But not right away. 

Harley-Davidson

According to brand historians, Harley (the man) pretty quickly realized that early Harley-Davidson singles just could not make enough power to satisfy customer’s demand for stronger engines. (We’ve always wanted more power, haven’t we?)

Toward that end, he believed the solution was simply adding a second cylinder to the existing one.

Stories about an upcoming Harley-Davidson “double cylinder” began appearing in trade publications in 1907 — just four years after the brand’s founding — and a 1908 story even showed a twin-cylinder H-D moto that won a Chicago-area hill climb event.

The following year, the brand’s very first V-twin-equipped bike appeared — and here’s where things go a bit pear-shaped.

Rolling off the production line in 1909, the Renault Gray Model 5-D boasted Carmine pinstriping, a 49.48 cubic inch (~811cc) V-twin engine making 7 horsepower and a price tag of $325.

Harley-Davidson

The 5-D was the only V-twin with its magneto in front of the engine, and the drive system was similarly unique. The belt had a pulley with some sort of internal centrifugal clutch, rather than the idler pulley that took up slack and engaged the engine on later production models.

With a redesigned gas tank and the brand’s first rear center stand, the 5-D proudly canted its twin cylinders 45 degrees.

Now, at the time, single-cylinder motors used an atmospheric intake valve that was opened by the suction created by the falling piston — essentially sucking the valve open. 

However, when applied to Harley-Davidson’s original twin-cylinder set-up, the extra volume made the suction less effective, and ultimately the intake valves just didn’t work right.

When this shortcoming became apparent, Harley-Davidson not only pulled the 5-D from production but also recalled the reported 27 bikes that had already been built … and destroyed them. 

Two-pronged triumph

Despite this pretty substantial failure, Harley-Davidson did not give up on the V-twin. 

The brand’s engineers spent the next year-plus rebounding and retooling, aiming for a power plant that could measure up to their lofty performance standards — and those of H-D’s customers.

So it was that 1911 saw the release of the Double Cylinder Model 7-D, complete with a new 6.5 horsepower F-head engine featuring mechanical inlet-over-exhaust valves. 

Harley-Davidson

This engine, later increased to 61 cubic inches and then 74 cubic inches, was such a strong and sturdy success, it was used all the way up through 1929, when H-D replaced it with the Flathead, or sidevalve. 

The stage had been set for so many stupendous V-twin engines to follow, including the Knucklehead, Panhead, Shovelhead, Evolution, Twin Cam 88 and the Milwaukee-Eight.

The most recent iteration, the Revolution Max 1250, made its debut with the brand’s groundbreaking first adventure bike, the Pan America, in 2021.

Harley-Davidson

Those are just the Harley-Davidson engines, though. You’ll see the unmistakable V-twin design on loads of other brand’s bikes, from Ducati and Indian to Moto Guzzi and Yamaha and so many more throughout the moto industry.

And even though it was such a dud that Harley scrambled to erase it, at least one of the first V-twin bikes survived. The only known 1909 H-D V-twin can be found in the Harley-Davidson Archives in Milwaukee. 

Oh, and the engineers got at least one thing about the original design just right. Because for 93 years, until 2002, every single Harley-Davidson V-twin engine was canted 45 degrees.

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