Rotary engine: The icon of Mazda- (2) The effort to improve rotary engine by Mazda

The new prototype

The first prototype of rotary had various advantages compared with traditional 4 stroke engine but it seemed not to be good for a production, which is because this engine should be disassembled when changing the spark plugs. In this reason, Wankel and NSU needed to improve the engine and developed new rotary engine called ‘KKM’ in 1958. In this engine, a water-cooled housing and an oil-cooled rotor were added and spark plugs are also set easily on the housing. It can say that current rotary engines have mainly been influenced from this KKM design. In November 1959, many auto companies were stimulated this rotary engine after official announcement of NSU and they tried to have its copyright for technical improvement. There were many the bidders including GM and Citroen, but among them, Mazda was especially zealous. Tsuneji Matsuda who was the president of Mazda could perceive its strong potential. Even he personally negotiated with NSU. Finally, Mazda could win the competition. They paid approximately 2.8billion in Japanese yen, which was excessive large sum of money for Mazda in fact –Some critics say that it was overmuch price compared with the rotary’s worth at that time.

matsuda ◀ Tsuneji Matsuda






Rotary engine has several advantages


In the rotary engine, the ignition is occurred three times per a cycle while the four-piston engine’s ignition is one time per a cycle. So it is more efficient even if the displacement is small.

In case of Mazda’s RX-8 which equipped rotary engine, for example, it has 1.3L engine but shows the performance of 232 horsepower and its torque is 22.4kg·m. Even it is possible to hit until about 9,000rpm.


Rotary engine spins in one direction unlike piston engine which operated by an up-and-down motion. This one direction spinning can make the vibrations decrease so help the engine being more balanced and less noisy.

Smaller and simpler

Compared with traditional engine, the rotary engine’s structure is simpler. In addition, the number of parts is smaller.

general engine

▲ Parts of traditional engine

rotary engine

▲ Parts of rotary engine





Begin of improvement

Mazda’s negotiation team came back with a brimming expectation and could obtain a single rotor of 400cc from NSU. Even Tsuenji Matsuda already organised a technical team for commercialisation of the rotary engine during negotiation. They were enthusiastic at the true that they can make an innovation soon. However, it was not easy. During researching of the rotary engine, they could discover fatal problems in terms of practical use. Representatively, there was the phenomenon called ‘chattered mark’. It indicates any of a series scratches or grooving trace on the surface. This chattered mark was arisen on the surface of housing, which means that the durability of the engine has critical problem –It was used to call that a nail mark of devil. Additionally, the leak of engine oil and fuel by the damaged housing from the chattered mark also gave the engineer of Mazda a hard time. For years, Mazda was struggling for discovering the cause and could find the reason. It was because of a part called Apex seal, which always made this problem and was worn out easily. To solve this problem, they developed ‘cross-hollow seal’ and equipped it a prototype, which could drive for 300 hours continuously at last.

14511_content ◀ Charttered mark

chattered mark

▲The housing damaged by chattered mark.







Mazda (n.d.). History of Rotary [online] available from <; [19 Dec 2013]

The Auto Channel (2004). The Wankel Engine History [online] available from <; [19 Dec 2013]

Autocar (2013). History of the Mazda rotary engine [online] <> %5B12 Dec 2013]

Autospeed (2008). The History of Mazda’s Rotary Engine [online] available from < > [19 Dec 2013]

Howstuffworks (n.d.). How Rotary Engines Work [online] available from < > [20 Dec 2013]





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