KENICHI YAMAMOTO AND THE CHATTER MARKS FROM HELL: THE MAZDA ROTARY ENGINE

As elegant and straightforward as it seemed on paper, Toyo Kogyo engineers quickly discovered that the rotary engine had many serious problems. At the time the license agreement was approved, even NSU had yet to build a truly production-ready engine, and the early single-rotor prototypes suffered a very rough idle and prodigious oil consumption. Cooling was also problematic and the gap in the water jacket around each spark plug housing produced thermal stresses that would eventually crack the rotor housing.

The biggest problems, however, were with the complex apex and corner seals at each rotor tip. Those seals were responsible for maintaining compression and segregating exhaust gases from the intake charge, but they experienced considerable stress from the combustion process, limiting their useful life. When the seals wore out, the engine suffered dramatic power loss. Few of the early tip seals had anything approaching an acceptable lifespan, usually failing after less than 200 hours of operation. Harder materials lasted longer, but exacerbated another problem: the tendency of the apex seals to leave vicious “chatter marks” on the inner surface of the rotor housing. During the first two years of development, Toyo Kogyo reportedly scrapped hundreds if not thousands of ruined test engines.

Although the Japanese engineers were progressing more quickly than their NSU counterparts were in some areas, the development process was undoubtedly expensive, and Toyo Kogyo might well have given up had it not been for the determination of Tsuneji Matsuda. The story among company employees was that the normally implacable Matsuda had actually kowtowed before Toyo Kogyo’s principal financiers while pleading for the resources to continue the rotary project. Whether or not that was true, Matsuda made it clear that he considered the rotary the key to the company’s survival — a commitment that eventually won over even one of the engine’s harshest internal critics, engineer Kenichi Yamamoto.

Yamamoto, born in Kumamoto in September 1922, had received a degree in mechanical engineering in 1944 from the prestigious Imperial University in Tokyo. Conscripted after graduation, he had been commissioned as a naval lieutenant and sent to work with Kawanishi Aircraft at the firm’s naval works in Tsuchiura, where he was eventually assigned to work on kamikaze aircraft. When the war ended, jobs for skilled engineers were scarce, so Yamamoto ended up as an assembly line worker at the Mazda plant in Hiroshima, which had only recently reopened after being damaged in the American atomic attack. Yamamoto’s articulateness and technical drawing skills (which he had continued to practice) did not go unnoticed, however, so a few years later he was transferred him to engine development, working on the design of Toyo Kogyo’s first OHV engine.

An early rotary engine, possibly a single-rotor NSU engine. In this view, the rotary’s compact dimensions are readily apparent. The engine itself is dwarfed by its air cleaner and carburetor, gearbox, and accessories. (Photo circa early 1960s, copyright and courtesy Mazda)

By his own account, Yamamoto was not pleased when the company licensed the rotary engine in 1961. He considered the rotary conceptually sound, but he was all too aware of the many pitfalls facing any new engine design and saw the whole project as a boondoggle and a waste of resources. Given those doubts, one can imagine his reaction when he learned in April 1963 that he had been reassigned to lead the new Rotary Engine Research Department.

Yamamoto’s first six months in his new job did little to assuage his doubts. Despite the dedication of his hand-picked engineering team, known internally as the “47 Ronin” (in reference to the famous group of masterless samurai whose quest to avenge their fallen lord in the early 1700s is popularly regarded in Japan as the epitome of honor, loyalty, and duty), the rotary engine’s major problems seemed intractable — particular the chatter marks, whose cause was initially elusive. Nonetheless, Yamamoto resolved to give it his best effort, particularly after he heard Matsuda deliver a speech to Toyo Kogyo suppliers that June, outlining the existential threat posed by MITI’s consolidation plans.

By the time Toyo Kogyo exhibited prototypes of the new rotary at the Tokyo Auto Show in October, Yamamoto had become so frustrated and discouraged that he told Matsuda he wanted to resign. Matsuda persuaded him to stay by appealing not only to Yamamoto’s company loyalty, but also to the memory of the siblings they had both lost in the bombing of Hiroshima.

Matsuda rewarded Yamamoto’s perseverance with an infusion of new resources. In 1964, Toyo Kogyo set up a state-of-the-art rotary engine lab with 30 test cells and computers to process the test data, still a novelty in the mid-sixties. Over the next three years, the company would quadruple the size of its rotary engineering staff.

Gradually, Yamamoto and his team came to grips with the rotary’s major flaws. The chatter marks were eventually traced to the apex seals hitting their resonant frequency within the engine’s operating range, which was addressed with changes to the seal design and materials. The apex seals of Mazda’s early production rotaries were self-lubricating pyrographite, impregnated with aluminum for greater strength, which eliminated the chatter marks and provided a useful life of at least 60,000 miles (100,000 km). Meanwhile, better oil seals, developed in partnership with Nippon Oil Seal Co. and Nippon Piston Ring Co., finally reduced oil consumption to a manageable level. By 1967, Toyo Kogyo was finally ready to launch its first rotary-engine production car.

MAZDA COSMO SPORT

To showcase its new engine, Toyo Kogyo decided to develop an entirely new car not based on any existing model. Known internally as Project L402A and later christened Mazda Cosmo Sport, it was the first Mazda sports car: a low-slung monocoque coupe with a very low hood line that took full advantage of the rotary’s compact dimensions.

Although Toyo Kogyo had gone to Italy for some past design work, the Cosmo Sport was styled in-house, looking rather like the bonsai offspring of a 1961 Ford Thunderbird and the 1963 Chrysler turbine car. Unlike Mazda’s early kei cars, the Cosmo Sport had a front engine and rear-wheel drive. Front disc brakes were standard and the sole transmission was a four-speed manual gearbox.

The early L10 Cosmo Sport was 163 inches (4,140 mm) long on an 86.6-inch (2,200mm) wheelbase, standing only 45.9 inches (1,165 mm) high. Curb weight was quoted at 2,024 lb (918 kg). The Cosmo Sport had quick rack-and-pinion steering, but some reviewers criticized it for being numb on center and complained that crosswinds response was less than reassuring. (author photo)

The earliest Cosmo Sport prototypes had a two-rotor engine known as the L8A, with a total swept volume of 798 cc (49 cu. in.). (Unlike NSU, Toyo Kogyo engineers had largely abandoned single-rotor engines, concluding that multiple rotors provided better low-end torque and idle quality. Mazda would briefly explore a return to the single-rotor concept in the 1970s in search of greater fuel economy, although they never offered a single-rotor engine in any production car.) To improve low-speed performance, the L8A had two spark plugs for each rotor, one firing 5 degrees after the other. To manage the separate advance curves for the twin plugs, there were two complete ignition systems, including twin distributors.

The first two running prototypes of the new car were finished by October 1963, and Matsuda actually drove one to the Tokyo Auto Show later that month. However, Toyo Kogyo displayed only the engines at that show, delaying the Cosmo Sport’s public debut until September 1964. According to some accounts, Matsuda opted to wait as a show of respect to NSU, whose first Wankel Spider had debuted in Frankfurt only a few weeks before the 1963 Tokyo show. According to others, NSU pressured Toyo Kogyo to delay the launch and discouraged plans to show the Cosmo Sport overseas, lest it steal the Spider’s thunder.

The Mazda Cosmo Sport had double wishbone front suspension with coil springs, but the rear was a de Dion layout with a fixed differential and a beam axle on semi-elliptical leaf springs, located by trailing links. The unassisted disc/drum brakes were adequate for the Cosmo Sport’s weight, but feel and pedal effort drew some criticism. In response, the L10B cars added a standard vacuum servo. (author photo)

Initially, the L8A had peripheral exhaust ports and a combination of side and peripheral intake ports, which linked to the primary and secondary barrels of the standard four-barrel carburetor. While the additional peripheral intake ports improved high-end power, Yamamoto’s team found them detrimental to low-speed response and idle quality and finally decided to delete them, leaving only the side intakes. That change left the L8A somewhat underpowered, so the engineers increased the rotor diameter, raising total swept volume to 982 cc (60 cu. in.). With a single Zenith-Hitachi four-barrel carburetor, the revised L10A engine was rated at 110 PS (108 hp, 81 kW) at 7,000 rpm, with a maximum of 96 lb-ft (130 N-m) of torque at 3,500 rpm.

Toyo Kogyo built about 60 preproduction cars for evaluation in 1965 and 1966, but the Cosmo Sport didn’t actually go on sale until May 30, 1967. It was not only the first production Mazda with a rotary engine; it was the world’s first two-rotor production car, debuting more than four months before NSU’s Ro80 sedan. (Curtiss-Wright had previously tested its two-rotor RC2-60 U5 engine in a modified Ford Mustang, but that engine was never offered for public sale.) Since Toyo Kogyo had only recently revised its license agreement to allow sales of the rotary engine outside Japan, the Cosmo Sport was initially offered only in the home market, with a starting price of ¥1,480,000 (around $4,100). Only a few cars ended up overseas, many of them purchased by other automakers or rotary licensees like Curtiss-Wright, who were eager to figure out what made the Cosmo tick.

The yellow, single-snorkel air cleaner marks this as a 110 PS (81 kW) L10A Cosmo Sport; the more powerful L10B had a blue air cleaner with twin snorkels. In either form, the 982 cc (60 cu. in.) engine was very compact and the use of cast aluminum for both the rotor housing and side housings kept dry weight to only 225 lb (102 kg), a full 90 lb (41 kg) lighter than Volvo’s comparably powerful B18 four. Note the twin distributors and ignition coils, common to most Mazda rotaries until 1974. (author photo)

The curious foreign journalists who had the opportunity to test the Cosmo Sport were mostly impressed. It handled well, with quick steering and basically neutral balance, but the real star was the engine. The L10A was not especially quiet (although some reviewers found its exhaust note quite charming), but it was exceptionally smooth and would rev to 8,000 rpm with an alacrity and enthusiasm alien to most contemporary reciprocating engines. Low-end torque was not abundant, but as engine speeds increased, performance brightened considerably. Reaching 60 mph (97 km/h) took less than 9 seconds and advertised top speed was 115 mph (185 km/h), impressive for a small sports car of the era, and faster than many V8-powered American sedans.

The Cosmo Sport was not sold in large numbers — only 343 were built between May 1967 and September 1968 — nor was it intended to be. Its construction involved a great deal of hand labor, and it’s hard to imagine Toyo Kogyo made any money on it. If the little Mazda coupe was not a profitable exercise, however, it was an effective proof of concept that drew attention from around the world, including many markets the company had yet to enter.

Even more attention came in August 1968, when Toyo Kogyo entered two Cosmo Sports in the Marathon de la Route endurance race at the Nürburgring. The Nürburgring cars had various engine modifications, including the restoration of the L8A’s auxiliary peripheral intake ports, but were otherwise close to stock. One car was felled by a broken axle during the race, but the other took fourth place, the first flush of a long and often illustrious competition career for Mazda rotaries.