‘The devil’s fingernail marks’
Evan Zabawski | TLT From the Editor November 2011
An elegant solution saved the rotary engine.
After five years of toil, the engine was finally ready for production.
My first car was a 1973 Mazda RX-2. That’s right, not an RX-8 but one of Mazda’s earlier rotary-powered vehicles. The tale of the RX, or Rotary Experimental, series from Mazda is one engine that almost wasn’t.
Mazda was originally a company in Hiroshima, Japan, called Toyo Kogyo, and before that fateful day on Aug. 6, 1945, they only produced three-wheeled industrial vehicles. Several months later, a young engineer named Kenichi Yamamoto, returning to his hometown to seek his family, joined the company. While the city rebuilt itself over the following years, Nissan and Toyota started producing automobiles on such a scale that the Japanese government chose to limit the number of automakers to three. Toyo Kogyo’s president, Tsuneji Matsuda, was determined to become one of Japan’s Big Three, and so he assigned Yamamoto to the head of development for a four-wheeled automobile.
Even though his efforts produced a mildly successful offering, Toyo Kogyo still faced being bought out. At this time Matsuda heard about a new type of engine conceived by Felix Wankel and was convinced this technology would save his company. In 1961 Matusda paid an exorbitant fee to license the rights to produce and further develop the Wankel engine, a task he assigned to an eager Yamamoto.
Yamamoto began testing the prototype, which he found belched thick, tarry exhaust. It was discovered that oil leaked through the face of the rotor into the combustion chamber. What was worse was that the engine simply stopped operating after only moderate use.
It seemed the apex seals on the rotor created grooves on the inner wall of the rotor housing, allowing gasoline to leak from the combustion chamber and ultimately flooding the engine. These grooves were referred to as “the devil’s fingernail marks,” and finding a material suitable for the apex seal would prove to be the greatest challenge of Yamamoto’s career.
After filling company storage rooms with failed prototypes, Yamamoto approached Matsuda apologetically asking to be removed from the assignment. Matsuda reassured Yamamoto that he felt he was the only one who could make the rotary engine work. Yamamoto then picked the best engineers in the company and rallied his team to sacrifice everything for the cause.
They managed to stop the oil leak with a rubber seal on the rotor, something that was never tried before for fear of melting, but it turned out the rotor ran cooler than expected. Over 500 materials were tried on the apex seal to banish the grooves. Some were too coarse and would scratch the inner walls, while others were too soft and caused excessive friction. One day, while doodling with his pencil, Yamamoto observed that his savior material was in his hands—graphite. Pencil lead resisted scratching but slid across paper remarkably well. The only issue was finding a way to make it hard enough to withstand the rigors of the spinning rotor.
Yamamoto asked his chief metallurgist, Jun Miyata, to come up with a solution. After many unsuccessful attempts, he was simply experimenting when he mixed it with a softer material, aluminum, and found his answer. A prototype was built and run on a test bench—no fingernail marks. It was installed in a test mule car that was run for 70,000 miles—still no fingernail marks. After five years of toil, the engine was finally ready for production.
The only hurdle left was proving to the world that this new technology could compete with pistons, and so it did in the 84-hour Marathon de la Route endurance race. Of the 26 of 51 cars that finished, Mazda placed fourth, proving the rotary engine was viable. Now entering its 45th year of production, you could say the rest is history.
Evan Zabawski, CLS, is the senior reliability specialist for Fluid Life in Edmonton, Alberta, Canada. You can reach him at evan.zabawski@fluidlife.com.