Uploaded October 2025 | Updated September 2026, 1 week ago
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BECOME A YOUTUBE MEMBER
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SOURCES
barchetta.co/rotary-engine-sources
TIMESTAMPS
0:00 INTRO
2:02 TOYO CORK KOGYO/PREWAR ACTIVITIES
7:24 EARLY SUCCESS
8:49 THREAT OF CONSOLIDATION
10:43 FELIX WANKEL
11:52 EARLY ROTARY ENGINE DEVELOPMENT
15:16 MAZDA DISCOVERS THE ROTARY
18:22 KENICHI YAMAMOTO
23:12 THE DEVIL'S NAIL MARKS
25:08 MORE ROTARY DEVELOPMENT
27:07 MAZDA COSMO DEVELOPMENT
32:51 MAZDA COSMO HISTORY
Mazda was not the only company interested in the technology. In The New Mazda RX-7 and Mazda Rotary Engine Sports Cars, author Jack Yamaguchi notes that over 100 firms sought a license, 34 of which were Japanese. Thankfully, NSU entertained Mada’s inquiry. Tsuneji and several other company representatives then visited its headquarters in Neckarsulm.
NSU granted Mazda a license on October 12, 1960, the 40th anniversary of the company’s founding. The deal wasn’t officially approved by the Japanese government until July 1961.
It cost the automaker 280,000,000, or $780,000, and allowed Mazda to use and sell rotary engines in Japan and Asia.
Soon after the agreement was finalized, the automaker formed the Rotary Engine Development Committee. This was a patchwork team comprised of members of the design, material research, production engineering, manufacturing, and test divisions. The deal also included some sample engines. Before these arrived in Hiroshima, engineers built test units based on the design of the KKM400. It was at this point that Mazda realized just how flawed the engine architecture truly was.
If Mazda wanted to make it a reality, then it needed to shore up its research efforts. The patchwork approach it had taken thus far had turned in disappointing results. Larger automakers with more resources could take that same approach and make more progress on their rotary programs. To keep pace with its contemporaries, Mazda needed to establish a department wholly dedicated to. It did just that in April of 1963, when it founded the Rotary Engine Development Division. To head it up, Mazda looked to a young, brilliant engineer.
Kenichi Yamamoto may have been born in the city of Kumamoto, but he had Hiroshima blood in his veins. His family moved there when he was a child. In 1944, Yamamoto graduated from the University of Tokyo with an engineering degree. This led to a job at the Kawanishi Aircraft Company in Ibaraki Prefecture, roughly 60 miles north of the nation’s capital. He returned to his hometown after the war ended and found it in ruins. His mother survived the bombing, though his sister perished.
Engineers primarily focused on improving engine durability. The rotor wore away at the inner surface of the housing, leaving behind ‘chatter marks’. They lowered compression and robbed the engine of power. The marks appeared after just 200 hours of testing. Both the NSU sample units and Mazda’s prototype motors suffered from the phenomenon. Employees became so annoyed by this issue that they began calling them ‘the devil’s nail marks’. The team found that they were caused by the apex seals vibrating against the housing. Some of the company’s research focused on reducing those unwanted vibrations. They subdued them by drilling horizontal and vertical holes in the apex seal. This significantly improved durability. Now, test engines could run for 300 hours before succumbing to the chatter market. While cross hollow apex seals wouldn’t be installed on production rotaries, the situation did inspire the engineers to think outside of the box.
BECOME A PATRON: patreon.com/BarchettaMedia
BECOME A YOUTUBE MEMBER
youtube.com/channel/UCZCB8ChAn8PQXzONCi193FQ/join
SOURCES
barchetta.co/rotary-engine-sources
TIMESTAMPS
0:00 INTRO
2:02 TOYO CORK KOGYO/PREWAR ACTIVITIES
7:24 EARLY SUCCESS
8:49 THREAT OF CONSOLIDATION
10:43 FELIX WANKEL
11:52 EARLY ROTARY ENGINE DEVELOPMENT
15:16 MAZDA DISCOVERS THE ROTARY
18:22 KENICHI YAMAMOTO
23:12 THE DEVIL'S NAIL MARKS
25:08 MORE ROTARY DEVELOPMENT
27:07 MAZDA COSMO DEVELOPMENT
32:51 MAZDA COSMO HISTORY
Mazda was not the only company interested in the technology. In The New Mazda RX-7 and Mazda Rotary Engine Sports Cars, author Jack Yamaguchi notes that over 100 firms sought a license, 34 of which were Japanese. Thankfully, NSU entertained Mada’s inquiry. Tsuneji and several other company representatives then visited its headquarters in Neckarsulm.
NSU granted Mazda a license on October 12, 1960, the 40th anniversary of the company’s founding. The deal wasn’t officially approved by the Japanese government until July 1961.
It cost the automaker 280,000,000, or $780,000, and allowed Mazda to use and sell rotary engines in Japan and Asia.
Soon after the agreement was finalized, the automaker formed the Rotary Engine Development Committee. This was a patchwork team comprised of members of the design, material research, production engineering, manufacturing, and test divisions. The deal also included some sample engines. Before these arrived in Hiroshima, engineers built test units based on the design of the KKM400. It was at this point that Mazda realized just how flawed the engine architecture truly was.
If Mazda wanted to make it a reality, then it needed to shore up its research efforts. The patchwork approach it had taken thus far had turned in disappointing results. Larger automakers with more resources could take that same approach and make more progress on their rotary programs. To keep pace with its contemporaries, Mazda needed to establish a department wholly dedicated to. It did just that in April of 1963, when it founded the Rotary Engine Development Division. To head it up, Mazda looked to a young, brilliant engineer.
Kenichi Yamamoto may have been born in the city of Kumamoto, but he had Hiroshima blood in his veins. His family moved there when he was a child. In 1944, Yamamoto graduated from the University of Tokyo with an engineering degree. This led to a job at the Kawanishi Aircraft Company in Ibaraki Prefecture, roughly 60 miles north of the nation’s capital. He returned to his hometown after the war ended and found it in ruins. His mother survived the bombing, though his sister perished.
Engineers primarily focused on improving engine durability. The rotor wore away at the inner surface of the housing, leaving behind ‘chatter marks’. They lowered compression and robbed the engine of power. The marks appeared after just 200 hours of testing. Both the NSU sample units and Mazda’s prototype motors suffered from the phenomenon. Employees became so annoyed by this issue that they began calling them ‘the devil’s nail marks’. The team found that they were caused by the apex seals vibrating against the housing. Some of the company’s research focused on reducing those unwanted vibrations. They subdued them by drilling horizontal and vertical holes in the apex seal. This significantly improved durability. Now, test engines could run for 300 hours before succumbing to the chatter market. While cross hollow apex seals wouldn’t be installed on production rotaries, the situation did inspire the engineers to think outside of the box.
