YAMAHA 250 ROAD RACER History of the Privateer's Best Friend*By Kevin Cameron
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YAMAHA 250 ROAD RACER History of the Privateer's Best Friend*By Kevin Cameron • In the years following World War II. you have no national motorcycle industry, cylinder to be sunk very deeply into the many riders in England and Europe you get a piece of someone else’s. By case, thus limiting fin area. The pistons learned roadracing on single cylinder license agreement and exchange of engi of the time were made, like car pistons, Manx Norton production racers. These neers, Europe’s motorcycle design tradi from a fairly soft, high-expansion alumi 500s and 350s were designed to be simple, tions were absorbed by the budding Japa num. These two facts made trouble for maintainable, and effective. Above all, nese manufacturers. About 1955, such an the racer. The gearbox held only four they were available. Those who didn’t race exchange took place between Yamaha and speeds, creating a further limitation. 30M and 40M Nortons very likely went the German Adler firm. Germany had Two stroke tuning in Europe was re to starting grids on AJS 7R and G-50 been the birthplace of effective two- ceiving a powerful impetus from the East Matchless models. Riders on their way up strokes with the prewar DKW machines, German MZ firm, which was building on were spared the tasks of engineer, ma and had continued to lead the world in the knowledge gained by DKW. Their chinist and financier, and were thus able two stroke design. The first Yamaha 1953 125cc racer gave a pitiful 9 bhp at to concentrate on riding. The British sin two stroke twins strongly resembled the 7800 rpm, well below the performance of gles gained a reputation as rugged, well- Adler. The carburetors were bolted to the contemporary four strokes. In the next engineered motorcycles. crankcases, feeding the cylinders through five years, they tried and discarded a fan A similar situation exists today, but the slots. The clutch was crankshaft-mounted. tastic array of strange designs, finally brand is different. Yamaha 250 production Rivalry among the new companies in emerging with what was to be the defini racers have been the standard mount for Japan was strong, and the leading race tive two stroke powerplant of the future. beginning roadracers for ten years now, of that time was the Mt. Asama cinder- This was the loop-scavenged, disc-valve- and they have dominated international track “roadrace.” Competing against such inlet engine, exhausting through a baffled 250 racing for five years. In any country now-defunct names as Tohatsu and Me- megaphone, or expansion chamber. The of the world where roadracing exists, you guro, the Yamaha company was deter 1960 version of this 125 single gave 22 will find most riders and tuners are thor mined to win this event, which took place bhp at 11,000 rpm, for a bmep (brake oughly familiar with these machines. in the shadow of Mt. Fuji. mean effective pressure) of 104 psi. The engines are derived from road This first Asama racer was the most Yamaha kept informed of trends in models, and at the present time, the distant forerunner of the production racers European design, and they too saw the frames, forks, and other important parts of today. The first machines were made advantages of this layout. They began are shared with the street-going counter with two different bore/stroke ratios, the their own work with this type, and brought parts as well. P model having the dimensions 54 x their first rotary valve racer to Europe in How has this situation come about? 54mm, and the PQ measuring 56 x 50. 1961. This 250 RD-48 model gave 35 bhp What combination of circumstances has In 1956, Fumio Itoh succeeded in win at 10,000 rpm, 94-psi bmep. The engine led this company to produce hundreds of ning the Mt. Asama event for Yamaha, was air-cooled, pump and gas/oil lubri basically simple machines that win both which increased the determination of the cated, and housed in an open-loop frame club events and international races? management to seek further successes. much like that of the G-50 Matchless. It Many companies in postwar Japan saw The Honda Motor Company could only was no match for the championship-win diversification as a key to economic sur look on enviously at this time, but later ning Honda of that year, but it added vival. Cheap transportation was needed, the two firms would meet in competition greatly to Yamaha’s growing knowledge of and motorcycles were a good answer. Ya on the Asama course, a foretaste of the racing two strokes. maha made the improbable jump from great European GP struggles they were While this European effort was getting pianos to motorcycles. The early machines to fight out years later. under way, management looked into ex closely resembled European models. If The design of the P model required the porting road machines to the United AUGUST 1974 77 M '**r *:•*,.« ifcs mil * •■$• V*>^ Reaching predominance in 1965, the little twin-cylinder two-stroke has been at the very heart of motorcycle pavement racing competition ever since. Along the way it has taught tuners how to tune, riders how to ride and winners how to win. Robert Winters, John Buckner and Ralph White, The 1960 competition machines, re two-stroke design. MZ. while long on all on Yamahas, in 1966. Winters won a squeaker. ferred to only as “Yellow-tankers,” were talent, was short of development money. States. The new American organization essentially RD-48 frames, wheels, brakes, From the 35 bhp of the RD-48, power and tanks, with the new piston-port ano- rose in 1963 to 48 bhp. 115-psi bmep at also decided to use competitive success to further sales and reputation, so Fumio dized-cylinder engines fitted. This new 11.000 rpm, and on to the final 1965 form, engine shared the crankcase of the iron- the RD-56, giving 56 bhp. 135-psi bmep Itoh came to compete in the Catalina races here in 1958. cylinder road model YDS-2. Instead of at 11.000. New knowledge was accumu Getting away in 47th position. Itoh the two piston rings of earlier models, this lating fast in the Yamaha camp. racer used a single ring 1.5mm thick. It amazed the onlookers by passing all but Encouraged by results with the “Yel gave a better compromise between friction two of his competitors up the first straight, low,” President Kawakami and US Gen then by broadsliding even the paved turns loss and life in racing use. eral Manager Skip Clarke decided to pro The new pistons and cylinders worked feet-up. His P model suffered its tradi duce improved racing machines and sell tional piston problems, and Itoh dropped much better than the early hardware, but them to anyone with the money to buy back. The following year, similar ma continuing trouble with the anodized cyl one. Racing in the US was slanted towards chines were entered in the events at Dodge inder surface led four stroke fans to call the production racer concept by the AM A City, and this time it was Larry Beale who the new Yamaha the fastest way from the Class C rules, which required a large start to five laps from the finish. demonstrated the surprising power of the quantity of complete racing machines for new machine. Once again the Yamaha Research continued which was financed approval. Selling 200 racers would put a was stopped by problems. by the considerable commercial success of large number of Yamahas on the start line Unreliability usually means either in the company. The main thrust of compe of any AM A 250 race, and basing the racer tition development w'as by now directed competent design or a very rapid rate of on a road machine would make the cost development. In this case, certain aspects toward the European theater where acceptable. If the machines were success ful, it would be a great boost to sales and of the design outstripped the capabilities Honda was making a worldwide reputa tion. The RD-series of air-cooled twins public awareness of Yamaha. of the rest of the machine. Yamaha had found that traditional ideas of port timing elevated the horsepower in the 250 class They did it. Even though the piston-port were much too conservative, and that rapidly, making Yamaha for the first time TD1-A, as it was called, used a frame the world’s foremost practitioner of great power could be unlocked from small already discarded by the GP program, it cylinders by long exhaust and transfer was good enough for a production racer. timings, used with the correct exhaust The brakes, tank, seat and other running pipe. This produces high piston tempera gear of the obsolete RD-48 were used as tures. as early release of exhaust means well, effecting a further savings—plans higher exhaust gas temperature. and jigs for manufacture already existed. For 1960. the P and PQ models were The first sales of the TD1-A took place dropped, and a new engine emerged. It in late 1962. It inherited the 27mm pot- was a notable advance. The cylinders were metal carburetors of previous models, all aluminum, and the carburetors fed along with the MC-2RY magneto and them directly. Pistons of much higher wide-ratio five-speed gearbox. Again, silicon content ran directly on the alumi metallurgy problems stopped many fine rides, but the production racer started num cylinder wall, which had been hard ened by anodizing.