Yamaha TZ

Yamaha TZ

Kenny Roberts 1974 Assen Yamaha TZEvery now and then a machine comes along that grabs the racing world by the scruff of its neck, and opens up a whole new range of possibilities for the private racer. Inconceivable in modern times, during the 70s, it was entirely possible to afford and buy a competitive machine from your local dealer and, with a little preparation, be the owner of a machine capable of winning a club race or grand prix alike. This machine was the Yamaha TZ twin, evolving from the air-cooled TD3/TR3, these buzzy two strokes turned out to be competitive, cheap to run and supremely reliable. The basic engineering involved meant the TZ was a doddle to work on too.

The TZ all but dominated the racing the globe over throughout the 70’s and very nearly lifted a few world titles too, keeping many other manufacturers honest as they did so. The crankcases and general layout of the TZ is very similar to those of an RD but that is just about where the bloodline ends. A six-speed close ratio gearbox forms the transmission and this was fed its vicious power via a large dry clutch and straight cut gears for extra energy transfer efficiency. The barrels are a one-piece liquid cooled affair allowing all of the tuning lessons learned during the sixties to be put into good use. The 250 was good for a reliable 50bhp in standard trim while the later versions of the 350 could put out well over 70bhp making them very handy tools to have around.

The TZ story begins for real in 1971 when air-cooled factory twins bikes first appeared with four lugs already mounted on the front down tubes, upon which the radiator could be mounted as and when required. By the end of that year the first prototype water-cooled top end was in existence ready for the start of the 1972 season. These were used to great effect by several favoured riders that season, but none more effectively than Jarno Saarinen, who clinched the 250cc championship that year, and finished a close second in the 350cc class behind Agostini and the MV Agusta.

Kenny Roberts Assen Special Yamaha TZBy the end of 1972 the Yamaha factory was ready to start production of the water-cooled production race machine, the TZ350 A. Based loosely upon the R5 roadster, no doubt to make it eligible for US competition, there was some notable differences, the primary gears provided the drive for the water pump, and the barrels were a one-piece design enabling the transfer ports to be larger than with separate cylinder castings.

Power output for the over-the-counter machine was a unprecedented 65bhp at 9,500 revs and it cost a very reasonable £1200.00. For this price you also got a comprehensive spares kit enabling a whole seasons racing without further expense, providing you stopped on it that is. This package, with no viable alternative, was enough to become the favourite mount for a multitude of riders from club level all the way though to GP’s. Once the power band was mastered the bikes were very easy to ride, the 350 being the more flexible than the 250. Saarinen gave the new water-cooled machine the perfect launch by taking one to the USA, beating the established Superbikes of the time to win the prestigious Daytona 200.

The 250cc version of the TZ followed the bigger machine into the dealer’s showrooms midway through 73 and was once again a great deal for the privateer. Many riders found that working on them was so easy they only had the one machine, choosing to change over the top ends between races, thus competing in both classes with little extra expense but with a potential increase in income should success be had in both races.

For the early TZ, the A/B, the chassis was lighter but virtually identical to the RD save for the necessary lugs etc used mount side stands and suchlike. The steel tubing of the TZ frame was much lighter, but even so the RD chassis made a good conversion into a pukka race machine. The Maxton range of TZ powered racers incorporated many of the road bike cycle parts, forks, discs etc in their TT and GP winning machines.

Kenny Roberts TZ YamahaYamaha placed great emphasis on their race successes with these RD based machines during the 70’s, but in reality they never did officially win the 250 championship as a factory effort. After the initial flurry following the bikes launch, Saarinen’s title in 72 and the one further privateer title in 73, when Dieter Braun took the overall victory, albeit with most points scored on his air-cooled TD3, the 250, TZ or OW never again clinched the crown. The TZ350 faired little better with one world title, when Jon Ekerold clinched victory with the Bimota framed, TZ powered, Solitude. In between those times only the factory 350cc OW machines ever won a world championship and these were wildly different from the customer version.

The OW 16 and, its smaller capacity sibling the OW17, first seen in 1973, looked exactly like the TZ from a distance, but keen eyed observers soon noticed the fairings were much shorter and higher off the ground; this was because the engine was a fraction of the size of the TZ. The OW racers where largely fabricated out of Magnesium and other lightweight materials so, at 29kgs (60lbs) lighter, they tipped the scales far lighter than any TZ. The crankshaft rotated backwards, enabling huge inlet ports without piston damage and the drive was then delivered to the clutch via a jackshaft taking its drive from the centre of the crank, in a similar way to the TZ500 and 750 fours. Power output was well into the high seventies and this was enough to give the Yamaha factory riders Agostini, and Johnny Cecotto, the title in 1974 and 75 respectively. They missed out on any title hope in 73 due to the untimely death of Jarno Saarinen and the subsequent withdrawal of the Yamaha team for the remainder of the season. The Monoshock frame was first seen on Agostini’s OW factory bikes towards the end of 1974 before becoming available to the public in 1976 with the TZ C model.

TZ350ACecotto began his 74 championship season with a TZ, but around the midway point of the year, when it looked like he could take the crown, Yamaha provided him with factory support, and with it came the OW16. That was to be the last world championship for the factory twins, Takazumi Katayama did become champ in 77 but that was achieved largely using the European developed 350 triple, based on one and a half TZ250 engines utilising a shorter stroke via TD2 crankshafts, to achieve the 349cc capacity.

The TZ, although not as successful as our memories would like us to think, was the tool to have for the privateer, as with little or no modification it was good enough to grab the odd race win here and there and score heavily in the overall standings. Many a professional racer relied on the good old TZ to earn his keep, every machine in the top ten of the 350 championship of 1975 was a Yamaha twin, either factory or private, a testimony to the types ability. Everywhere the race spectator looked, whether it was at a club meeting, or international event, the Yamaha twins were prodigious. There was precious little you could do to tune them without seriously affecting the reliability, so riders knew that they stood an equal chance at whatever level of racing they participated.

The Yamaha engine was generally very tolerant of all kinds of abuse and many featured conversions enabling the use of the 350 in the 500 class where, in the absence of other commercially available machines, it was a force amongst the lower rankings during the early and mid seventies. The common mod was the fitting of an eccentric crank pin increasing the stroke by half a millimetre, and with it the capacity to 351cc, enough to let it into the premier GP class.

Kenny Roberts Assen TZ YamahaVery little was done to the TZ over the ten years of continued production, the single most drastic change came in 1976 when, to bring it in line with the 1975 factory bikes, the C was introduced with radical Monocross suspension and the single disc brakes used on both the front and rear wheels. This replaced the twin shock suspension and the massive four leading shoe brake arrangement of the previous models and at £1500 for the 250, was met with great enthusiasm by the racing fraternity. For the first two years of its life the TZ had been modified in such a way by a multitude of specials builders like Harris and Spondon so Yamaha were finally giving the public what it really needed.
Pretty soon every top racer in the UK had a C model, and the outdated drum braked bikes were either converted to a disc set up, using mainly RD parts, or consigned to club level.

The subsequent D and E models were little different from the C only minor internal modifications, like revised port timing, was deemed necessary. For the rider, the most important improvement would have been a new design of forks, the front end pattered under load but nothing much was ever done about by the factory, it being left to the suspension specialists to cure. The next, and final, transformation came about in 1979 when the F model was announced. This was a development of the machine that Kenny Roberts and his team had built in readiness for his assault on the 250 world title in 1978. Once again the Roberts machine bore little resemblance to the commercially available version with its extensive use of machined down components and trick parts.

Yamaha TZ350ARoberts had used a trick TZ in a GPs some four years before (Actually the yellow and black bike seen here) when he endured a one off ride at Assen, leading the race by a good margin before stepping off towards the end of the race and rejoining to finish 3rd. That race was also very nearly the end of the Californians GP hopes, Kenny recalls “luckily I remounted to finish third and as stood on the rostrum I just kicked off about the amount of money I had just won for a GP placing, and believe me it was a pitiful amount, I could easily have earned more in the US club racing! So when the man with the microphone came around and stuck it in front me, instead of praising my sponsors, I carried on with the rant about the clowns paying to work in the circus.”

It may well have been true, but it went down like the proverbial lead balloon with the organisers so much so that when Kenny and his team left that day, it was made quite clear, that it would be some time before he would be allowed back into the GP’s. Luckily he did return.

The overall design of the F “Lowboy” layout gave the impression of a shorter wheelbase, when in actual fact it was 5mm longer than the previous models, with the tank sat well into the frame tubes and much effort made to reduce weight. Manoeuvrability was addressed via a sharper head angle and, on paper at least, the bike had the makings of a winner. The F model was well received but it soon became apparent it was little better than the previous E version, the front end still pattered terribly and the headstock tubes cracked. This problem carried over into the G series and became so bad that Yamaha had to replace all of the TZ frames, most of them with English built Harris or Spondon replica items.

Yamaha TZ350The 350 F suffered incredible piston wear, thanks to an increase in inlet port area, while the 250 was a poor performer against the latest Rotax powered machines that were starting to be developed to great effect. Yamaha’s immediate answer was the TZ250G, this featured an increase in bore size giving a capacity of 249cc, and whopping 8mm removed from the rear of the piston skirt, saw the power up by 4bhp.

To calm down the rush of power the power jet carburettors from the 350F were used to boost midrange. By now the price of a new TZ had doubled over the price of the 1976 C model and with little improvement was becoming not such a good proposition. The forks stanchions were made thicker, and were re-valved internally, in an attempt to stop the patter, but in reality this never worked and the bike disappeared almost without trace into a sea of Rotax powered inline twins.

The following year, 1981, and for the quarter litre class anyway, the original TZ story was over. Yamaha had the all-new TZ250 H, complete with a price increase to £4500 but it really was half of the factory OW48 racer, with its power valve exhaust mechanism, separate crankshafts, and pressurised lubrication to the gearbox.

TZ350Despite its short life, and the up coming end of world championship status for the capacity, the TZ 350G was a success, and once the chassis problems were sorted perhaps, the best they ever made, continuing to be a favourite mount for many a future star, actually carrying on unchanged into the early eighties with the 350H model. In 1982 the 350cc GP class was dropped forever and with it came the death knell for this little machine at world level. They did live on however with many rolling chassis being robbed for the upcoming Formula two series and a new series, The Promoters 350 class, to be run a national level in the UK keeping the remaining TZ’s operational. The sidecar boys also had a use for the twin cylinder engines using it almost exclusively in the F2 championship until the 600 four-stroke engines caught on and subsequently took over.

Yamaha TZ350A Specifications

Engine – liquid cooled, twin cylinder, two-stroke, piston port
Capacity – 347cc
Bore/stroke – 64 x 54mm
Power – 64bhp @ 9500rpm
Torque – 35ft-lb @ 8200rpm
Carburetion – 34mm Mikuni VM34SC
Transmission – 6-speed dry clutch chain final drive
Frame – steel tube cradle
Suspension – 34mm telescopic forks. Twin shock rear
Brakes – 260mm double twin leading shoe drum. 220mm twin leading shoe drum
Wheels – 3.00 x 18 3.00 x 18
Weight – 115kgs
Top speed – 145mph
Wheelbase – 1331mm
Fuel capacity – 23ltrs

Kenny Roberts Assen Special TZ Yamaha

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Yamaha TZ350A Gallery

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