Arnas from Illinois has rebuilt a 1985 BMW K100RT into a custom café racer he calls Shadow. He kept the original frame lines but upgraded nearly every part of the bike. His goal was to create a clean, dark-themed motorcycle with modern features and strong performance.
The original K100RT was a touring motorcycle. It was made for long rides with comfort and reliability. Arnas chose it for its strong engine, durable build, and simple design. These features made it a good base for his custom project.
Shadow keeps the core of the K100RT but replaces its old parts with better, newer components. It blends original structure with new tools, finishes, and controls.
Base Bike Origins: The 1985 BMW K100RT
The BMW K100RT was first built for long-distance travel. It came with a full fairing, upright seating, and a strong inline-four engine. Riders liked it for its comfort, low vibration, and smooth power. Police and touring riders often used it for daily and highway use.
This model used a water-cooled engine. It gave stable performance in different conditions. The K100RT also had a shaft drive instead of a chain. This made it easy to maintain and more reliable over time. The frame was strong and carried the weight well.
Because of its simple and open layout, the K100RT became popular among custom builders. It offered space for changes and upgrades. Its clean engine lines and basic shape made it easy to restyle. Arnas chose this bike for its proven base and the chance to improve every part.
Builder’s Approach: Classic Shape, Modern Soul
Arnas built Shadow to look modern but still respect the original lines of the BMW K100RT. He did not want to fully change its identity. He kept the main shape but removed all extra parts that did not serve function or style. His goal was to create a clean, dark, and bold look using smart upgrades.
He used different shades of black to define the bike’s new visual tone. Matte, gloss, and satin finishes were chosen to create contrast without adding extra parts. He removed tank covers to show the metal body and highlight the factory shape. Every change was made to support the clean style.
Arnas also focused on visible details. He sanded the engine fins by hand to show the metal edges. This gives the bike a vintage look that matches older BMW styles. He used small and hidden lights to reduce clutter. Shadow stays low, simple, and tight. It shows a strong balance between old design and new function.
Engine & Mechanical Overhaul
Shadow uses the original engine, but almost every internal part was cleaned, restored, or replaced. The previous owner rebuilt the engine before Arnas started the project. New piston rings were installed to improve compression and extend engine life. The valves were cleaned and adjusted to factory specs for better airflow and smooth running.
All seals and O-rings inside the engine were replaced. This step prevents oil leaks and helps the engine work more efficiently. The oil and coolant pump was rebuilt using an upgrade kit from KPARTSHOLAND. This change supports better cooling and longer engine health.
The throttle bodies and alternator were both removed, cleaned, and coated with heat-resistant Cerakote. This not only protects them but also gives a clean, dark finish. Arnas made sure the engine looked neat on the outside and worked well inside. These updates make the bike more reliable and help it deliver better power with less risk of failure.
Custom Frame & Bodywork
Arnas modified the rear subframe by cutting, extending, and welding it to fit a slimmer shape. This gave the bike a lower rear profile. The new frame section supports a solo seat and matches the sharp look of the build. He used a seat cowl from Twisted Brothers, which fits tightly with the new frame.
The original gas tank was stripped to bare aluminum, cleaned, and painted. He chose to keep it uncovered to show the clean metal surface. This adds contrast to the dark body and highlights the center of the bike. A CNC-machined aluminum gas cap was added for a better finish.
Many metal parts were powder-coated. This includes the frame, swingarm, engine covers, and brackets. Powder coating protects the parts from rust and adds a smooth surface. Each part was blasted or cleaned before coating to remove old paint and dirt. This process gave Shadow a clean, strong structure with no weak spots.
Performance & Handling Upgrades
Shadow includes many changes that improve how the bike rides and responds. Arnas installed new clip-on handlebars from Protaper. These sit lower and give the rider a sport-style riding position. The new position brings more control during turns and faster movement.
He added CNC-machined levers for smoother clutch and brake feel. Rearsets were also installed to move the foot controls higher. This change improves ground clearance and gives the rider a more balanced body angle. The rear brake reservoir was relocated for a cleaner setup and better access.
A perforated rear brake disc replaced the stock unit. This upgrade helps with cooling and gives better brake performance. All brake lines were replaced to ensure safety and improve pressure. These changes help Shadow stay sharp and firm at both low and high speeds. Each upgrade supports handling and fits the bike’s clean design.
Electronics & Lighting
Shadow includes a custom electronic system focused on both function and style. At the center is a 5-inch Deep Moto touchscreen speedometer. It shows speed, tilt angle, altitude, and other riding data. It also has built-in front and rear cameras that record while riding. The screen supports both Apple and Android phones.
Arnas moved the ignition key to a custom holder near the radiator. This clears space around the handlebar area. He also added a battery charging port under the seat for easy access. The battery itself was relocated under the rear seat cowl to keep the frame open.
All lights were replaced with small, modern LED units. A DOT-approved headlight was installed in the front. Slim turn signals were mounted on the forks as running light strips. Compact LED units handle brake and signal duties in the rear. CNC-machined control buttons were added to the handlebar. These give a clean look and simple control without extra switches.
Design & Paint: The Shadow Effect
Shadow follows a full blackout theme using only black finishes in different tones. Arnas used matte, satin, and gloss layers across the frame, tank, engine, and smaller parts. Each finish was selected to highlight the part’s shape without adding extra color.
The gas tank was first sanded to bare metal, then painted in jet black. This finish blends smoothly with the bike’s overall blackout style. It adds depth without drawing extra attention. The engine covers, swingarm, and rear frame were powder-coated in matching dark tones. These finishes protect the parts and give the bike a sharp, unified appearance.
Lights and controls were also finished in black. The mirrors, levers, grips, and buttons follow the same dark palette. Small details, like the diamond-stitched seat and matching grips, tie the design together. Arnas sanded the edges of the engine fins to expose bare metal. This adds contrast and brings a vintage touch to the modern finish. The result is a balanced mix of visual depth and mechanical focus.
Riding Style & Experience
Shadow is built for riders who prefer control and sharp response over comfort. The clip-on handlebars place the rider in a forward-leaning position. This makes the bike feel direct and sport-focused. It improves steering input but may feel aggressive for new riders.
The solo seat is thin and shaped for style. It matches the café racer look but offers limited padding. This makes short rides enjoyable but may not suit long trips. The rearsets also move the feet higher and farther back. This setup helps in fast turns but needs a balanced riding posture.
The engine pulls strong across gears. The upgraded injectors, air filter, and exhaust help it respond quickly. The deep sound from the custom 4-to-1 muffler adds to the feeling. Every movement feels connected. Shadow rides like a machine meant for serious road use, not for quiet travel. It gives full control to the rider at every speed.
Final Thoughts
Shadow is the second bike Arnas has built in this style. After the success of the first, he chose to take this one further. The goal was to keep the familiar café racer shape while improving every detail, both inside and out. The result is a cleaner, more advanced version that still respects the original lines of the BMW K100RT.
Every part was selected with purpose. The frame remains classic, but nearly everything else has been upgraded. Shadow now includes modern features like a touchscreen dash, front and rear cameras, LED lighting, and a fully rebuilt engine. These updates improve both performance and control without changing the bike’s original spirit.
The blackout theme defines its appearance. The gas tank, sanded to bare metal and then painted jet black, completes the bike’s dark and focused look. Nothing feels out of place. Every surface, control, and line fits the theme without distraction.
Shadow is not a copy of other builds. It reflects clear planning, hands-on work, and a strong vision. Built by one person with simple tools and a clear goal, this motorcycle is designed to ride, to perform, and to be seen.
About the Builder: Arnas (@nakromedia)
Arnas is a custom bike builder based in Illinois, USA. He has worked on many café racers and scramblers over the years, combining practical skills with a clear design approach. His passion for motorcycles began early, helping his father repair bikes and cars. That hands-on experience shaped his knowledge and love for mechanical work.
His interest in BMW customs began the day he saw his first café racer from the brand. That moment had a lasting impact and helped define the direction of his own builds. Since then, he has focused on mixing classic forms with modern upgrades.
Arnas is also a skilled photographer. He documents each project through high-quality photos that show both detail and design. For him, building and photographing bikes are part of the same creative process. Each build reflects his personal style and careful attention to balance, finish, and function.
Follow Arnas and see more of his work on Instagram at Nakro Murando.
Disclaimer
This article is based on information, build notes, and public statements provided by the original builder, Arnas. All technical details, modifications, and specifications are shared for editorial and enthusiast purposes only. I do not claim ownership of the motorcycle or direct involvement in its construction. Images, brand names, and parts mentioned are used to accurately describe the build and are the property of their respective owners. The goal of this article is to highlight the craftsmanship behind the project and to support the custom café racer community through detailed documentation.
