“The Ideal Big Single” – KTM 690 Duke

Super Single: KTM 690 Duke “Road Sport” by 46works…

In 1969, a Norton Manx piloted by Godfrey Nash was the last single-cylinder machine to win a 500cc Grand Prix. Even as multi-cylinder machines came to dominate road racing tracks over the last 50 years, however, many racing organizations continued to run single-cylinder “Supermono” or “Singles” classes, typically featuring bikes up to 800cc.

The exotic 916-derived Ducati Supermono is the best-known machine to grow out of supermono racing — in fact, it’s become nearly synonymous with the term — but machines such as the MZ Skorpion, Yamaha 400/500 singles, and even the Suzuki Goose 350 have served as capable track mounts over the years.

What’s more, it seems that sporting singles may be making a comeback, with Ducati recently unveiling their new Superquadro Mono and Suzuki filing patents for a supermono engine. Anyone who’s ridden a big single in anger knows why. Twins have their heart-like syncopations and fours their furious howls, but there’s nothing quite like a single piston the size of a boxer’s fist punching up and down at WOT.

One man who’s long seen the sporting potential of single-cylinder machines is Shiro Nakajima of Japan’s 46works, who got his start on a Yamaha SR400 in the late 90s:

“It was the heyday of racer replicas, but I was riding around on that SR400, at full lean through the mountain passes. To me, a big single bike is not a nostalgic object, but a sport bike.”

Fast forward more than 30 years, and that guiding principle would lead to the machine you see here today. Says Nakajima-san:

“I have always wanted to create the ideal big single sport someday.”

His donor would be a 2017 KTM 690 Duke, packing one of the most rambunctious single-cylinder road-going engines on the planet: the LC4. KTM is duly proud of the fact that this engine has manage to transform the modern riding public’s conception of big singles:

“The LC4 has shaken off the stigma that large-capacity monos are too aggressive in their delivery and vibrate too much to be practical. The latest generation LC4-powered machines offer versatility with a truly unique riding experience…” –KTM

In this incarnation, KTM’s LC4 has a cylinder bore of 10.5 cm (4.13″) and maximum power output of 72 bhp at 8500 rpm. Matched with WP suspension and a weight of just 148.5 kg (327 lbs), the 690 Duke was a hooligan sport rider’s dream.

“It will turn with very little effort and will drop to toe scraping angles of lean with ease. You don’t really need to hang off or manhandle it, simply look where you want to be and you’re there.” –MCN

Nakajima-san, who has a reputation for building race-bred customs, fully tested his 690 Duke in stock trim before beginning his transformation. His focus was to transform the bike into a “road sport” without disrupting the engineering, ergonomics, and overall performance of what was already a highly capable machine.

“The stock Duke has the waist-high styling of an off-road bike, but I thoughtfully designed it to express low, compact road sport styling — without lowering the suspension or riding position… Lowering is one of the easiest ways to make a bike look cool, but I am always thinking about making a cool bike without doing so.”

The fuel tank, seat cowl, truss subframe, fenders, airbox, and electrical box are all one-off pieces shaped from aluminum, while the slip-on exhaust is titanium.

The top yoke is another one-off, machine to allow the use of clip-ons without altering the riding position too much. Shiro is especially proud of the mirrors, developed in collaboration with Japanese company TANAX and available for purchase next year.

Then there’s the paint laid down by Drops Design Works: a lime-green scheme that recalls that of the early Dukes, boldly eschewing the earth-tone palettes so popular today.

“This is the antithesis of those colors. Doing something unusual can cause rejection, but I don’t mind and move on.”

Indeed. It takes the vision and perseverance of a true artist to push against the grain, and Nakajima-san has succeeded in creating another work of art in radiant, roaring motion. We can’t wait to watch the master carve his new KTM through those mountain passes of his youth!

In the Builder’s Words…

In the late 1990s, the first motorcycle I acquired was a Yamaha SR400. It was the heyday of racer replicas, but I was riding around on that SR400, at full lean through the mountain passes. To me, a big single bike is not a nostalgic object, but a sport bike.

At the time, it was popular in Japan for some enthusiasts to race single-cylinder bikes, and the races were so exciting that some failed to qualify. The majority were SR and SRX tuned bikes, and in later years the Suzuki Goose also participated.

Over the next 30 years, several big single sportbikes were launched, but they were produced in small quantities or were expensive. So I have always wanted to create the ideal big single sport someday.

About 15 years ago, I rode a KTM Duke for a test ride for a magazine and was very impressed with the LC4 engine, which felt like a tuned single racer. With this engine I decided to build a single sportbike.

When this project, “Building the Ideal Big Single Sport” began, I tested the 2017 KTM 690 Duke I had purchased in its fully stock condition. I test-rode on city streets and mountain passes, and I also tested the racetrack at full throttle. As a result, I preferred the more flexible handling using the full suspension stroke, so I decided to create a road sport without changing the body posture, ride height, or suspension stroke.

The stock Duke has the waist-high styling of an off-road bike, but I thoughtfully designed it to express low, compact road sport styling — without lowering the suspension or riding position. I do not see anything good about lowering a bike, except for the footing aspect, in my opinion. The lower you make it, the more boring handling the bike becomes. So on every bike I have ever built, I have not done any custom lowering. Lowering is one of the easiest ways to make a bike look cool, but I am always thinking about making a cool bike without doing so. I am satisfied that KTM has succeeded in doing so this time as well.

The candy green coloring was said by many in the audience to be unexpected. But in my mind, it is one of the ideas I had saved up. Early models of Duke existed in a lime green color.

Especially in Japan today, earth colors and old-looking solid colors are in vogue, and such colors are often used in new models released by automobile manufacturers. This is the antithesis of those colors. Doing something unusual can cause rejection, but I don’t mind and move on.

This time I made the top bridge (triple tree) with a general purpose milling machine. That is because the clip-on handles are mounted on the top bridge without lowering the ride height,
for both styling and an easy position. This is also to mount the stock meter in a compact manner.

The aluminum box under the seat is an air box that uses the factory air cleaner element and also serves as a mount for electrical components and the battery. Although not visible in the photo, the air intake is located behind the rear suspension and is funnel-shaped. All factory functions such as ABS and traction control are movable.

Finally, about rear-view mirrors. When a custom bike is built and mirrors are installed at the end, the bike often looks instantly uncool. To avoid this, until now I have often made one-off mirrors.

There were many requests for the commercialization of this product, and it was jointly developed with TANAX, one of Japan’s leading mirror manufacturers, which will be commercially available in the spring of next year. I installed a mass production prototype of it on this vehicle.

Build Sheet

2017 KTM690DUKE custom

One-off Aluminum fuel tank
One-off Aluminum seat cowl
One-off Aluminum seat rail (truss frame)
One-off Aluminum Air cleaner box & electrical box (Can use stock air cleaner element)
One-off Aluminum fenders
One-off footrest
One-off seat (Urethane and surface skin by Razzle Dazzle)
Front mini-fairing with extensive modification of general-purpose products
One-off triple-tree (top bridge)
Clip-on Handle (Battle Factory)
KIJIMA Turn Signals
One-off Titanium slip-on exhaust
General-purpose dry carbon undercowl (Future’s Craft)
Spoke wheels for other KTM models
Painted by Drops Design Works
Etc.