The MIGHTY TZ500

Honda’s exit from the GPs arguably did Yamaha a huge favour – at Grand Prix level it really didn’t have too much to worry about other than MV Agusta. And at privateer level it was essentially free to mop up whenever and wherever at 125, 250 and 350 events. It was only the premier blue-riband 500 level that Yamaha was lacking a creditable challenger… but plans were already afoot.

The year 1972 had seen the unveiling of a new road-going prototype – the GL750. A liquid-cooled four with fuel injection, the bike was aimed fair and square at Honda’s CB750/4 and Suzuki’s GT750/3… or was it? Many have suggested the GLs displayed were just mock up with many parts fabricated from wood and sprayed to look like aluminium. The very fact that Yamaha latterly rolled out the awesome TZ750 with a very similar engine design was hardly coincidence surely?

In reality the GL750 was partly a sabre-rattling exercise designed to wrong-foot the opposition. Yamaha had vowed to take on Honda in the sales rooms and the very notion of a four-cylinder two-stroke sold to the general public must have got The Big Aitch jiggy. And, of course, by adding fuel injection to a quartet of cylinders the Iwata factory was, in essence, sticking two fingers up at both Suzuki and Kawasaki by saying… ‘Look what we can do better than you!’ Ultimately the GL750 never made it to production due in no small part to the oil crisis of the early 1970s but, as a design exercise, the investment wasn’t wasted. The GL donated its DNA to the big TZ750 and, suitably shrunken, facilitated Yamaha’s entry into the world of half-litre Grand Prix racing.

Yamaha, the ever logical thinker, had spent the very early 1970s looking long and hard at its TD250 and TR350 race bikes. Both had begun life around the start of the 1960s as sporting developments of the firm’s road bikes. However, as the decade began to draw to a close it was apparent that performance gains were getting harder to attain. Even when fed the top racing oils of the day, seizures were still happening on occasion and the racing development team must have realised it had hit a glass ceiling. Knowing liquid cooling had been key to winning world titles with the breathtaking RA31A 125 and RD05A 250 V4s it was obvious where the future lay. Latterly limited by the FIM to just two cylinders at 125/250/350 levels, Yamaha took the TD and TR twins and gave them water jackets. Having already followed this approach with the 125cc racing twins campaigned so successfully by Kent Andersson, the new 250/350 duo was able to donate its cylinder and head architectures to both the TZ750 and the all-new TZ500. The latter was essentially a pair of TZ250s buckled together but on a single crankcase and the bike simply flew – often eclipsing the chassis in the process.

Developed in secret over 1972, the TZ500 aka OW20 was unveiled at the French Grand Prix with 250 world champion Jarno Saarinen on board. Already hugely successful on Yamaha’s 250/350 twins, the Finn had been persuaded at the eleventh hour not to sign up to ride the Italian Benelli 500/4 and it proved to be the correct decision. Saarinen took first place from Englishman Phil Read on an MV Augusta with Japanese teammate Hideo Kanaya third. Due notice had been served that Yamaha had arrived at the premier level!

WORDS: Steve Cooper, VJMC

PHOTO: Mortons Media Archive