Mazda had to tame the devil's fingernails before its rotary engine could work
When Mazda first tested a Wankel rotary in the early 1960s, the seals at the rotor tips vibrated so hard they gouged ripples into the housing. Engineers called the scars devil's fingernails. Solving them, along with a terrible thirst for oil, launched six decades of rotary cars from one stubborn company.
German engineer Felix Wankel invented the engine in the 1950s. Instead of pistons, a triangular rotor orbits inside a rounded housing, and Mazda's first prototype, the single-rotor 40A, closely resembled one built by NSU. It never went into production, but it exposed the two big flaws. The chatter marks came from tip seals vibrating at their natural frequency, and heat-resistant rubber seals on the rotor sides curbed the oil burning. Hollow cast-iron tip seals in the two-rotor L8A, shown at the 1963 Tokyo Motor Show, shifted that resonance and ended the scarring.
The first production rotary, the 10A, arrived in 1965 in the Cosmo. Its name hinted at its size: two chambers of 491 cc made about one litre. Later families followed the same logic, so the 12A displaced roughly 1.1 litres and the 13A about 1.3. Nearly all of them shared a rotor radius of 105 mm, the rare 13A being the exception. In 1974 a 12A became the first engine from outside western Europe or the United States to see the chequered flag at Le Mans after 24 hours, and in 1991 a four-rotor Mazda won the race outright.
Measuring these engines is oddly tricky. The output shaft spins three times for each turn of the rotor, so a full cycle takes 1080 degrees rather than the 720 of a four-stroke piston engine. Most racing bodies settled the argument by doubling a rotary's quoted displacement instead of asking everyone else to halve theirs.
Rotaries earned a name for being small and powerful but thirsty, which also made them favourites of kit-car builders and light-aircraft designers. After the RX-8 ended in 2012, Mazda built them only for a racing series until 2017. In 2023 the engine returned in a new role, as a generator in the MX-30 plug-in hybrid.
Source: Mazda Wankel engine
