Aeternum Blade: Rough Crafts Transforms the Harley-Davidson Street Bob Into a Modern Chopper

• Base: 2024 Harley-Davidson Street Bob with Milwaukee-Eight engine
• Displacement increased to 128 cubic inches (2,097 cc) via big-bore kit
• Fully custom girder fork with Öhlins damper, CNC-machined and partially 3D-printed

Winston Yeh from Taipei has completely transformed a 2024 Harley-Davidson Street Bob into a radical chopper. The “Aeternum Blade” combines classic chopper geometry with cutting-edge suspension components from Öhlins and Beringer. The engine was bored out to 2,097 cc and breathes through a carburetor instead of fuel injection.

Who Is Behind the Aeternum Blade Build?

The Aeternum Blade comes from the workshop of Winston Yeh, founder of Rough Crafts in Taipei, Taiwan. Yeh has built a reputation in the international custom scene over more than a decade and is considered one of the most prolific customizers in the industry. His trademark is dark, muscular motorcycles with an extremely high level of craftsmanship intended to rival factory quality.

What sets Rough Crafts apart from many other custom shops is the working method. Yeh’s workshop in Taipei’s Songshan district contains neither welding equipment nor milling machines nor a traditional mechanic’s garage. Yeh sees himself primarily as an industrial designer, not a mechanic. He completed his studies at the Art Center College of Design in Pasadena, California, where he earned a Master’s degree in Industrial Design. He then worked nine months at Roland Sands Design in the United States before founding Rough Crafts in 2009.

“My strength is with industrial design, so I will stick to design. As you see, my shop has no fabrication, no nothing. I have very limited tools… I don’t even trust myself to put bikes together. So I source experts in fabrication, assembly and paint.”

For each project, Yeh assembles a dedicated team of specialized suppliers. Depending on the requirements, CNC machinists, craftsmen, painters, and assemblers are brought in, each doing only what they do best. Yeh describes this approach as a deliberate choice: anyone who does everything themselves is limited to their own abilities. Those who delegate can push the boundaries of what is possible.

What Makes the Harley-Davidson Street Bob the Ideal Base?

The 2024 Harley-Davidson Street Bob belongs to the Softail family and is considered a stripped-down bobber focused on the essentials right from the factory. In stock configuration, the Milwaukee-Eight engine produces 94 hp (69.1 kW) and delivers 161.3 Nm of torque at 3,000 rpm. Standard equipment includes a 2-into-2 exhaust system, a chain primary drive, and twin-piston rear brake calipers.

It was precisely this simplicity that made the Street Bob the ideal starting point for Yeh. He describes the stock machine as a blank canvas that practically begged for a radical architectural transformation. He stated his goal clearly:

“The goal was clear: to recreate the essence of an old-school chopper, without sacrificing the precision and ride quality of today’s engineering.”

How Was the Street Bob Frame Modified?

The build began with the frame. The Rough Crafts team cut the steering head and repositioned it 6.35 cm (2.5 inches) upward and 1.27 cm (0.5 inches) forward. The original steering head angle of 30 degrees was retained. This modification creates a compact, forward-climbing silhouette characteristic of classic choppers. Unlike many traditional choppers with extremely long wheelbases, the Aeternum Blade remains compact and maneuverable.

This modified frame geometry formed the foundation for the most striking component of the entire motorcycle: a fully custom-developed girder fork.

What Is Behind the Custom Girder Fork?

The Aeternum Blade’s girder fork is a combination of three manufacturing methods. CNC-machined billet aluminum parts, 3D-printed components, and handcrafted elements were assembled into a skeletal fork construction. Inside the linkage, an Öhlins HD207 damper handles the suspension duties.

Girder forks are among the oldest suspended fork designs in motorcycle engineering and were widespread until the 1940s before being replaced by telescopic forks. In the custom scene, they have experienced a renaissance in recent years because they are visually striking and can be combined with modern dampers. Yeh has used girder forks in previous projects, such as his Sportster chopper “Mad Raider,” which also features a CAD-designed and CNC-machined girder fork with Öhlins damping. The experience from these projects likely influenced the Aeternum Blade’s construction.

At the rear, the original Softail swingarm was retained but upgraded with a fully adjustable Öhlins HD503 shock absorber. The combination of Öhlins components on both axles elevates the Aeternum Blade’s suspension well above the level of a typical show chopper.

How Was the Engine Upgraded to 2,097 Cubic Centimeters?

The stock Milwaukee-Eight engine was fitted with a 128-cubic-inch big-bore kit (equivalent to 2,097 cc). Specific power figures after the conversion have not been disclosed.

Perhaps the most unusual decision of the entire project concerns the fuel delivery. Instead of keeping the modern electronic fuel injection of the stock Street Bob, Yeh converted the engine to a classic S&S Cycle Super E carburetor. This analog conversion was made possible by an Altmann Carb Conversion System, which connects the carburetor via an Altmann intake manifold to a proprietary Rough Crafts air filter.

In an era when electronic engine management systems are the gold standard, reverting to a carburetor represents a deliberately purist decision. The S&S Cycle Super E is a butterfly valve carburetor that has been known in the Harley custom scene for decades as a straightforward and capable alternative to fuel injection.

The exhaust system is a one-off piece from Rough Crafts, fabricated from stainless steel. Unlike many current custom bikes where raw, colored stainless steel exhausts with visible pie-cut weld seams dominate, Yeh had all weld seams ground smooth and the stainless steel mirror-polished.

What Brakes and Wheels Does the Aeternum Blade Have?

The braking system comes entirely from Beringer, a French manufacturer that has been a staple in the Rough Crafts workshop for years. Up front, a 6-piston caliper works on a custom-machined disc carrier, while a 4-piston caliper at the rear sits on an individually fabricated bracket.

The wheels were supplied by Fatboy Design, an aftermarket wheel manufacturer. The “Kustom Snowflake” wheels measure 21 inches at the front and 18 inches at the rear, wrapped in Metzeler Cruistec tires. The combination of a large front wheel and smaller rear wheel follows the classic chopper proportion and further emphasizes the motorcycle’s stretched silhouette.

Why Does the Paint Scheme Deviate from the Typical Rough Crafts Style?

Black is the Rough Crafts trademark. The vast majority of Yeh’s builds are presented in various shades of black with contrasting details in carbon, brushed aluminum, or gold leaf. With the Aeternum Blade, Yeh deliberately departed from this formula.

He had the Frisco-mounted tank with deep contours and the matching rear fender painted in Nardo Grey by Rover Works Custom Paint in Taiwan, a color originally from the automotive industry known for its matte elegance. The grey finish was then adorned with hand-applied silver leaf in an engine-turned pattern and framed with precise pinstriping.

The grey color scheme extends across the stretched frame and the girder fork, creating a deliberate contrast to the mirror-polished metal surfaces on the engine. These include rocker covers and a camshaft cover from a collaboration between Rough Crafts and Arlen Ness, one of the best-known aftermarket manufacturers in the Harley scene. A mirror-polished transmission cover completes the look.

How Is the Aeternum Blade’s Cockpit Designed?

The cockpit follows the skeletal design language of the entire motorcycle. Minimalist mini ape hanger handlebars without risers and with little pullback float freely above the exposed joints of the girder fork. The absence of risers gives the handlebar area a clean appearance and underscores the reduced proportions.

A flat solo seat serves as the seating, handcrafted in collaboration between Rough Crafts and leather specialist Rich Phillips of Rich Phillips Seat Co.

What Role Does the Aeternum Blade Play in the Custom Scene?

Since its founding in 2009, Rough Crafts has completed commissioned builds for manufacturers such as BMW, Yamaha, MV Agusta, and Royal Enfield. What makes the Aeternum Blade particularly notable within the Rough Crafts portfolio is the combination of classic chopper architecture with modern manufacturing technologies such as CNC machining and 3D printing.

In interviews, Yeh has emphasized his desire to make custom culture more accessible. In 2023, he organized the “Speed and Crafts” show in Taipei featuring 50 custom bikes from Taiwanese builders and Japanese jurors. The event attracted approximately 5,000 visitors. His approach of using modern production motorcycles as a base pursues a specific goal: anyone who rides a stock model in daily life should be able to see themselves reflected in a custom build.

The Aeternum Blade fits into this concept. It uses a current production motorcycle as its base, which despite radical changes to the chassis and engine remains rideable and was not conceived as a pure show bike.

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