Yamaha RD350

Giant killer

| January/February 2010

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    The Yamaha RD350.
    Photo by Robert Smith
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    The Yamaha RD350.
    Photo by Robert Smith
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    The Yamaha RD350.
    Photo by Robert Smith
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    The Yamaha RD350.
    Photo by Robert Smith
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    Salvage yard reject: Hard as it is to believe, this carcass of a Yamaha RD350 is what Ian started with.
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    The detail work on Ian Swift's Yamaha RD350 is nothing short of amazing. Plastic film on the left engine cover protects it from scratches.
    Photo by Robert Smith
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    Ian's Yamaha RD350 may be almost perfect, but that doesn't keep him from firing it up for a quick run.
    Photo by Robert Smith
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    The Yamaha RD350.
    Photo by Robert Smith

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Yamaha RD350
Years produced:
 1973-1975
Claimed power: 39hp @ 7,500rpm (claimed)
Top speed: 95mph (period test)
Engine type: 347cc air-cooled, 2-stroke parallel twin
Weight: (wet) 352lb (160kg)
Price then: $1,071 (1975)
Price now: $1,500-$4,000
MPG: 35-40

Contrary to popular opinion, there’s no evidence supporting the idea that the “RD” in the Yamaha RD350 model designation stands for “Race Derived” — but race derived it certainly was.

Yamaha jumped into racing in Japan as soon as its first motorcycle, the 1955 125cc YA-1 “Red Dragon,” was launched. Early ventures into the U.S. racing scene were successful enough to encourage the company to widen its horizons. Yamaha factory rider Fumio Ito might have won the 1963 Isle of Man TT aboard the 250cc Yamaha RD56 if it hadn’t been for a bungled 50-second fuel stop. And when Ito was sidelined by a crash in 1964, Phil Read went on to take the 250cc Grand Prix world title. Yamaha factory teams continued to dominate the 125 and 250 classes at world level until 1968.

350cc or bust

Despite the early racing success of Yamaha motorcycles, it took a privateer team to crack open the 350cc class. In 1967, Canadian Yamaha importer Trev Deeley modified two 250cc Yamahas, punching them out to 350cc, and entered the U.S. racing scene with riders Yvon DuHamel and Mike Duff. DuHamel led the Indy National briefly that year before crossing the line just behind Cal Rayborn riding a Harley-Davidson 750, while Duff qualified second fastest at the 1968 Daytona 200, which Rayborn also won. The giant-killing era of the nimble 350cc 2-stroke was underway.



In 1967, Yamaha launched its first 350cc street bike, the YR-1. As little more than a big-bore version of Yamaha’s 250cc twin, the YR-1 can trace its ancestry to the YD-1 of 1957, which Yamaha engineers designed after carefully studying the M250 and racing RS250 twins from Adler in Germany. By 1962, the 250 had evolved into the 19hp YD-3 roadster with a pressed-steel backbone frame and electric start, and it was joined in 1963 by the sporty (but kickstart-only) 25hp YDS-2.

The big development came in 1964 with the YDS-3. Until then, almost all 2-strokes were lubricated by mixing oil with the fuel, a tiring and haphazard process that also required always having a bottle of 2-stroke oil at hand. Yamaha’s innovation — called Autolube — was carrying engine oil in a separate tank, injecting it into the engine at the carburetor by way of a small oil pump driven by the transmission input shaft. The fuel/oil ratio was determined by engine speed and throttle opening.

samblust
5/31/2018 8:40:41 PM

Wrong again. Whoever wrote that the brakes on the RD were mediocre never rode one hard. In my opinion as an owner and road racer of tow RD's I know they were GREAT. My races were won on the front brake. The rear brake didn't matter because under racing braking the rear wheel got so light from weight transfer you needed barely a touch on the rear, if at all. If you had troubles with one of the recently rebuilt bikes I'm going to say it's the tires. I don't remember what tires I was running but non stock period tires stopped fine. When I switched to Dunlop road racing tires it got even better. I worked parts at Boston Cycles in '69 through '72. It was interesting watching Yamaha's progression at the time. BC had road racers working at the shop and provided assistance/sponsorship to several riders. Many of the parts from the road racing 250 and 350 were directly usable on the RD. My own RD crank is built with TR parts, and the heads are TR. In production class racing of the period the only bikes that could beat us on the RD's were the few reasonably agile big bore bikes, and there were only a small few of them. On courses that had longer straights we would run out of steam at about 100, 105 and they could continue to higher speeds. But we got them back in the turns.


samblust
5/31/2018 8:34:45 PM

By the way, "R" is Yamaha's designation letter for 350cc. "L" was 125, "D" was 250, "G" was 80, "M" was 305. That's about all I remember of that. For me it was over 40 years ago.


samblust
5/31/2018 8:34:44 PM

Wrong again. Whoever wrote that the brakes on the RD were mediocre never rode one hard. In my opinion as an owner and road racer of tow RD's I know they were GREAT. My races were won on the front brake. The rear brake didn't matter because under racing braking the rear wheel got so light from weight transfer you needed barely a touch on the rear, if at all. If you had troubles with one of the recently rebuilt bikes I'm going to say it's the tires. I don't remember what tires I was running but non stock period tires stopped fine. When I switched to Dunlop road racing tires it got even better. I worked parts at Boston Cycles in '69 through '72. It was interesting watching Yamaha's progression at the time. BC had road racers working at the shop and provided assistance/sponsorship to several riders. Many of the parts from the road racing 250 and 350 were directly usable on the RD. My own RD crank is built with TR parts, and the heads are TR. In production class racing of the period the only bikes that could beat us on the RD's were the few reasonably agile big bore bikes, and there were only a small few of them. On courses that had longer straights we would run out of steam at about 100, 105 and they could continue to higher speeds. But we got them back in the turns.







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