This motorcycle is a one off custom build by Cohn Racers, a company widely known for its Muscle R2 projects and high end engineering focused motorcycles. While most of our work centers around those builds, from time to time we take on something completely different, purely for the challenge, creativity, and enjoyment of building something unique. This Honda Grom project was exactly that, a fun but highly engineered departure from our usual work, executed with the same attention to detail and standards that define all Cohn Racers builds.
The project began with a zero mile 2018 Honda Grom chassis. From the start, the goal was to create a compact motorcycle with real race bike character while maintaining balance, rideability, and durability. We had seen multiple Grom builds fitted with 250cc engines and even larger powerplants, but many of those setups felt excessive for the chassis and often compromised handling, reliability, or overall enjoyment. After careful consideration, we determined that a 125cc two stroke engine would be the ideal choice. It delivers strong, exciting performance without overpowering the platform, keeping the bike agile, controllable, and genuinely fun to ride.
For the engine, we sourced a Yz 125 from a 2016 bike, a brand new unit. The chassis was modified to accept the two stroke engine, and one of the most critical and challenging aspects of the build was addressing vibration. Two stroke engines are known for harsh vibration, especially when installed in lightweight frames. To solve this properly, we engineered a fully rubber mounted engine setup. Several custom components were machined specifically for this purpose, allowing the engine to be isolated from the frame while maintaining rigidity and alignment. This solution dramatically reduced vibration and transformed the riding experience, making the bike far more refined and enjoyable than a typical engine swap.
A Pro Circuit exhaust system was used, with only minimal modification required. The goal was to preserve the original exhaust ratios and performance characteristics while adapting it cleanly to the Grom chassis. Cooling was also carefully considered. The water cooling system was positioned at the front of the motorcycle to take full advantage of direct airflow. This layout works in conjunction with the front air intake, ensuring consistent cooling and reliable performance even during aggressive riding.
To make the motorcycle fully functional for street use, the stator was modified to generate electrical power. This allows the bike to run a headlight, brake light, turn signals, and a speedometer, making it a true street motorcycle rather than a track only build. From the beginning, this bike was designed to be ridden on the road, not just admired.
Structurally and dynamically, the bike received significant upgrades. An aluminum swingarm was installed to add rigidity and improve rear end stability. Suspension was handled by Öhlins front and rear, including Öhlins internals, giving the bike excellent control, confidence under braking, and composure at speed. Braking performance matches the engine and suspension upgrades, with Brembo brakes, super enlarged front rotors, a larger rear rotor, and fully custom brake lines throughout the bike.
The bodywork is a full fiberglass race style kit that gives the motorcycle the look and presence of a true race bike. This bodywork was sourced from a specialized manufacturer in Asia and then custom painted. Just like the engine, the bodywork is also mounted on rubber, a detail that required careful planning and fabrication. This approach reduces vibration transfer, improves durability, and gives the bike a much more refined feel than most custom builds in this category.
Attention to detail is evident throughout the motorcycle. The frame was fully powder coated prior to final assembly. The wheels are fitted with ceramic bearings. Carbon fiber protectors and accent components are used across multiple areas of the bike, including the rear sets and other high wear sections. Custom clip ons were fabricated, and every component was assembled with consistency, fitment, and finish in mind. The seat is upholstered in Alcantara, adding both comfort and a premium touch. The bike runs soft slick tires, which perform exceptionally well on the street and complement the aggressive nature of the build.
On the road, the bike is an absolute rocket. The combination of low weight, sharp power delivery, proper suspension, and serious brakes makes it incredibly exciting to ride. It has the raw character of a two stroke but with a level of refinement that is rarely achieved in custom engine swap projects. Every ride feels special, engaging, and purposeful.