The three-cylinder Yamahas

Last time we saw how Honda chose to potentially rewrite the rules for the 500GP class by offering an alternative engine layout. This time we’re looking at a maverick Yamaha 350 that had no official factory backing, but still delivered the goods. By the time of the mid-1970s more than a few riders were finding Yamaha’s TZ250/350s lacking for various reasons. Japanese rider Takazumi Katayama in particular was finding it tough going in his bid to be Japan’s first world champion; fortunately fate lent a hand.

Gifted eccentric Rudi Kurth had begun work of a 500cc Yamaha triple engine aimed at sidecar racing. The theory was three pots would provide more torque than the TZ750 four motors fitted with TZ250 cylinders that were then currently used in the outfits. By reducing the stroke, the unofficial half-litre Yamaha was something singularly unique. When ex-Yamaha racing engineer Ferry Brouwer heard of the engine he was intrigued by the concept and especially so now that he was working for Ton van Heugthen Motors. Contacting Minoru Tanaka, former head of Yamaha Racing, who offered support, spare parts and tuning data were supplied. It was while working on the half-litre triples that Brouwer came up with the idea of a 350 triple based around the TZ250’s barrels whilst using the splined crankshafts of the old, air-cooled, TD2 racers. Allegedly, Tanaka managed to liberate a significant number of these 50mm stroke crank assemblies which, when combined with the 54mm stroke of the TZ250s, gave a motor that was 343.3ccs in size.

Initial shakedowns and races for the new machine showed the cranks were weak so the team approached German specialists, Hoeckle, to build a ‘ground-up’ all new crank for the triple. Hoeckle had already gained a well-earned reputation for supplying aftermarket cranks for the conventional twins so the decision to outsource was hardly a gamble. By adding just 0.5mm to the crank’s throw the engine now came out a more conventional 346.8ccs.

Analogues of Kutrth’s half-litre triple did well in 1976 and this ‘proof of concept’ had convinced Takazumi Katayama to have a serious crack at the 1977 350 world title. Producing some 15bhp more than its twocylinder stepfather the bike, named Sankito, proved to be devastatingly effective. With Katayama and Giacomo Agostini riding the hybrid triple, it began to make serious inroads in the world championship. However, mid-season the Italian opted to revert to the twin, which he found was easier to ride on some of the tighter circuits and even Zooming Taxi, the nickname the Japanese rider had earned for himself, defaulted the more nimble twin on occasion.

A crash and fire at Chimay, Belgium, wiped out the original bike almost entirely so a Nikko Bakker frame was used for the subsequent races and at Imatra, Finland, Takazumi Katayama became Japan’s first official GP World Champion. That the triple wasn’t perfect was a given and, for some tracks, the more agile official 350 was the better bike. However, the team’s foresight and expertise had very effectively proved the concept. Further vindication of the idea came with the 500/3 which, when gifted a Spondon Engineering chassis, saw Kees van der Kruijis taking third place in the 1977 World Championships.

In an ideal world perhaps Yamaha themselves might have followed up on what was almost a private entry, but no. Triples were ultimately associated with rivals Kawasaki; no one at the Iwata R&D team had been involved (or ever considered the concept) and Yamaha had bigger fish to fry. The all-new RD350LC road bike was under development and the factory wanted

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it associated directly with the racing twins, not some apparently random three-pot wonder knocked up on a business park in Holland!

And so the bike that won Yamaha the 1977 350 crown was quietly mothballed and never spoken of again at HQ.

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