Too often lost amongst all of that signature bright orange paint, is just how good KTM has been over the decades at building some of the best engines in their respective categories. Whether you like your strokes to come in lots of two or four, from big singles to fancy twins of all types and even a racing-winning MotoGP four. Some Thirty-five years ago, KTM engineers developed the brilliant LC4 engine, and having ridden one many moons ago, master builder Shiro Nakajima promised himself one day he would build a racer for the road based on that glorious platform. And today is the day he unveils his incredible creation, from his humble home in the small 46Works garage, comes his 2017 KTM 690 Duke, resplendent with its lime paintwork, super single performance and one hell of a sexy silhouette.

When it comes to the custom motorcycle world, Nakajima-san has literally done it all and has nothing to prove, other than to himself. A trained engineer of the highest of standards, he built a public profile as the head of Ritmo Sereno, where vintage racers and retro mods were built to perfection. Along the way, he has always been held in high esteem for his technical knowledge, riding skill and metalwork mastery, and as he retreated to the Yatsugatake Mountains to start a new chapter, with the small operation that is 46Works, he has sought to infuse all of these talents into one incredible build at a time.

Perhaps best known for his work with BMWs, it was 15 years ago when a major magazine asked him to test ride a KTM 690 single, and it instantly tugged at the heartstrings of his youth. Having owned and raced a Yamaha SR400, he never saw the single-cylinder bikes as a retro remake, but as a true sport bike with their own unique characteristics. So, having fallen in love on that test with the LC4 engine, it was in 2023 that he finally purchased a 690 Duke to serve as a donor for his latest project. But rather than just strip it down and begin building, he rode first it everywhere; from back hills to highways, rutted roads and onto the race track.

“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 and without lowering the riding position,” Nakajima-san tells us. His experience teaching him that the WP suspension was excellent as is, and it would destroy the scalpel-like handling to change it, even if that means fewer parts changed on the spec list for bragging rights; such things don’t bother a true master! He did however decide that reducing the unsprung mass would be of benefit, as it always is, so a set of spoked KTM wheels from another model bolt-on, wrapped in Pirelli rubber.

The roller was then stripped of all of its orange plastics, placed on the hoist and strapped down to undergo surgery. Pulling large sheets of aluminium from the shelf, Nakajima-san began the arduous task of shaping both a fuel cell and a cover to begin the bike’s transformation. The meditative and meticulous way he goes about this process can be enjoyed on the 46Works YouTube channel. Each piece offered up to the bike, hammered on the bag, rolled through the English Wheel and only when it’s perfect, neatly tacked into place. Small cutouts are made for clearance, a fuel pump mount has been machined on a lathe, and the function is as flawless as the form.

Before the rest of the bodywork could even be started, Nakajima-san first unbolted the stock subframe and commenced the process of building his own. The steel trellis design picks up its inspiration from the main frame and has a hint of ’80s Ducati in its style. But it’s also an entirely functional piece and not a simple support, as housed within its confines is a large one-off aluminium air and electrical box, with the single-cylinder requiring plenty of oxygen on demand, and is fed by a rear-facing funnel, with provisions made to utilise the factory air cleaner and also host all of the bike’s electrics, for an ultra neat finish.

Then the meticulous metal shaping could resume, with the seat pan supporting a full-length tail section, with the cowl picking up the lines of the fuel tank, before enveloping a round, vintage-style taillight. The underside of the piece is all shaped to serve as a working rear guard, but it’s the front guard that steals the show, its symmetry as flawless as anything you’d see on a high-end supercar.

The front mask with a conventional headlight was the final piece of metal work, and then it was over to Drops Design Works to lay down the lime green, heavily inspired by a long forgotten factory KTM colour. Sitting between the bodywork, the custom seat is by Razzle Dazzle and Future Craft produced the dry carbon belly pan, that helps to visually lower the ride.

Being a skilled racer and fabricator, the next move was to machine a custom upper clamp, which supports the factory dash but allows for the fitment of Battle Factory clip-on bars. To match, the rearsets are another entirely custom-made part, flawlessly executed, and not wanting to disturb the lines, tiny Kijima turn signals have been added. But the right mirror could not be found, so of course, one was jointly developed with TANAX and will be available to the public soon.

To complete his masterpiece and really let that single sing, a full titanium exhaust and handmade muffler make for a stunning final addition. Nakajima-san is without doubt one of the true ‘Old Masters’ of the craft and when it comes to super singles, he simply reigns supreme.

[ 46WorksInstagram ]