How Mazda Conquered the Devil’s Nails in the Mazda Cosmo Rotary Engine
- Candace Watkins
- 1 day ago
- 3 min read
In the early 1960s, Japan’s automakers were still known for tiny city cars and economy sedans. The country was rebuilding and learning fast but few outside Japan believed it could compete with Europe’s engineering or America’s horsepower. Then a small company from Hiroshima decided to gamble everything on an engine that most engineers considered impossible to tame. If Mazda could make the experimental rotary engine work, Japan would not just catch up. It would leap ahead. Mazda decided to try what no one else had managed.
The Rotary Engine That Nearly Failed Everywhere
The company licensed Felix Wankel’s experimental rotary engine from NSU in Germany. The design promised compact size, smooth operation, and surprising power. It should have been revolutionary. Instead it became a disaster for everyone who tried to build it. The apex seals at the tip of the triangular rotor would vibrate and carve damage into the housing, a rippled pattern engineers grimly nicknamed the Devil’s Nail Marks. Compression dropped, oil consumption soared, and the engines failed. NSU struggled with the problem in the Spider and Ro80. Other companies gave up entirely but Mazda did not.
Mazda’s Breakthrough That Saved the Rotary
Mazda established a dedicated rotary research division and pushed ahead when everyone else walked away. Engineers tested new materials, redesigned the seals, and experimented with advanced coatings for the housing. After years of trial and error they created a carbon aluminum apex seal that finally survived long term running without scarring the engine’s internal surfaces. Once the chatter marks stopped appearing, Mazda knew they had achieved something unique. They had made the rotary engine reliable.
Now the company needed a car bold enough to show the world what they had done.
The Birth of the Mazda Cosmo Sport 110S
The result was the Mazda Cosmo Sport 110S. First shown as a prototype at the 1963 Tokyo Motor Show and launched in 1967, it became Japan’s first rotary powered sports car and one of the world’s first twin rotor production models. Its styling was sleek and futuristic, with a low roofline, covered headlights, and an instrument panel that felt closer to an aircraft cockpit than a traditional coupe. Even the name Cosmo was chosen to capture the era’s fascination with space exploration.
Tadanori Yokoo and the Iconic Rotary Brochure
Mazda hired pop artist Tadanori Yokoo to create the Cosmo brochure. It exploded with psychedelic colors, comic book typography.
A Hand Built Halo Car With a Revolutionary Engine
Hand built at roughly one car per day, the Cosmo carried Mazda’s breakthrough 982 cc twin rotor engine. It revved smoothly to 7,000 rpm and produced power comparable to a much larger piston engine. In Japan, where taxes were based on displacement rather than output, the rotary offered strong performance with a lower annual tax cost.
Proving Rotary Reliability at the Nürburgring
To prove the technology under the harshest conditions, Mazda entered two Cosmos in the 1968 Marathon de la Route, an 84 hour endurance race at the Nürburgring. One car lasted 82 hours before suffering axle failure. The other completed the full 84 hours and finished fourth overall. That result demonstrated that the rotary engine Mazda had perfected could survive one of the toughest races in the world.
How the Cosmo Sport Shaped Mazda’s Future
The Cosmo Sport became the foundation of Mazda’s identity. It proved Japan could innovate rather than imitate, and it launched decades of rotary powered machines including the RX 2, RX 3, RX 7, RX 8, and eventually Mazda’s Le Mans winning 787B.
A small hand built coupe had defeated the Devil’s Nails and changed Mazda’s future forever.
See it at the Tampa Bay Automobile Museum.