Back in the seventies, when gaffa tape across your leathers counted as body armour, the Japanese finally consigned the four stroke racing machine to the dustbin of history. They finished them off with tyre-shredding monsters like the Kawasaki KR750 triple, the Suzuki GT750 and the Yamaha TZ750.
All were 170mph plus two strokes; evil handling, under-braked and liable to seize their engines, or snap their drive chain, usually about three laps from the end of a race. In other words, typical classic motorcycles.
Chris Pearson rode a TZ750 around Cadwell Park, to understand why those 1970s road racing heroes chain-smoked and drank aftershave at the weekends. Alastair Walker flicked through the history files.
I have wanted one of these things ever since I was a boy when I saw a similarly aged Ron Haslam beat, the then World 500 champion and works MV Agusta mounted, Phil Read, on an early version of the big Yam. The TZ750 was, and still is, a monster of a machine, often referred to as “The Beast” even today. The bike still crops up in articles about all time great racing tackle and those that rode them in their heyday often talk of them with fond affection.
It is a common mistake that the 750 four is just two 350 engines coupled together, nothing could be further than the truth as it is actually based on the 1973 factory 500 four GP machine and shares no common components at all with the smaller roadster based twin.
Well the opportunity to ride one came and, as you can imagine, I jumped at the chance. These machines are still run competitively today with the Forgotten Racing association and it was with this club that I was riding. Lining up on the grid at Cadwell Park on board an ex-Jon Ekerold TZ750, I didn’t know what to expect. I knew for certain I had nowhere to put my knees. The TZ is all engine and exhaust pipes with very little in the way of creature comforts.
Practice went reasonably well but it was hard to assess my rate of progress as I was forced to familiarise myself with the TZ, whilst circulating with more modern machines, it did hold its own in a straight line with all but the fastest of new tackle however. I was more than a little cautious, as this powerhouse of a bike has to be run on skinny, treaded, eighteen-inch rubber, rather than the pukka racing slicks it was originally built for.
On board the TZ750 is a harsh environment indeed with the massive engine revving away, like an unexploded bomb, just inches from every body part and nothing in the way of comfort to soften the edges of the experience.
Practice passed without occasion and then it was time for the race. There were several similar 750s, a few RG500 Suzuki’s, with the bulk of the grid made up of buzzy little 250 and 350 twins. I was on the second row of the grid and the noise from the two stroke machines was distracting to say the least.
The grid took its time to mass and my heart was starting to pump. The big Yam is not designed to be sat around and pretty soon, without any air passing through the radiator, the temp gauge began to rise beyond the recommended 65 degree optimum way up towards the 80 mark. Luckily the hold up soon passed and it was visors down and ready for action.
The flag dropped and off we shot, heading for the very sharp club hairpin, I waited a little, braking very early to be on the safe side but no one came past, we were in the lead!
Gingerly around the right hand hairpin, then making sure the bike was upright before I unleashed the 120 plus horses underneath me, and off we set. We got to the first part of Charlies and still no one made an attempt and so it remained for some three laps of the demanding short circuit. I settled in after the first couple of laps feeling my way in this new environment of multi cylinder, two-stroke madness. The four-pot engine was actually very torquey and usable, although big handfuls of throttle lit up the rear tyre in all but top gear. I had the front pawing the air occasionally even whilst cranked over. Unusually for a two stroke there is even a reasonable amount of engine braking on tap.
Surprisingly the Avon tyres, very narrow looking by today’s standards, gripped incredibly well with predictable levels of adhesion. Stopped by twin Lockheed calipers up front, acting on a pair of 290mm Yamaha steel discs, this provided braking power as good as anything I have ever ridden. There was plenty of feel all of the way into the apex of a corner, then the superb chassis takes over, keeping it ship shape around the twists and turns of Cadwell.
I was starting to take a few liberties with the big Yam and exiting Charlies got the rear tyre spinning up, which felt perfectly safe, at no time causing me to back off, it just served to tighten the bikes turning abilities, reducing the amount of lean required in the process. Eventually I had to give way to 350 mounted Lea Gourlay as he out braked me into the hairpin.
The big Yam and I hung on to the back of the former 250 MRO national champion, but we had to settle for second place as the 750 struggled to cope with the nimble 350 twin around the undulating Lincolnshire track. Trying to run at Leas pace on the heavy 750cc four left me a wee bit out of breath by the end of the nine-lap race. He could simply get the power down far sooner than I could, most of the time Gourlay was accelerating while I was pulling huge wheelies, although once the 750 was upright it would start to reel him in.
I really wasn’t expecting to be taking such a ringside seat in the proceedings. If anything I had been planning to have a play around in the mid field until my confidence with the powerhouse machine grew. So 2nd place was a real result.
Having also ridden the TZ350 I can say the little twin really is the ideal machine for the Cadwell club circuit, the TZ750 just does not have the right sort of attributes to take on a smaller, more nimble machine around here, although this was my first ride on “the Beast”.
Since that debut, the opportunity has arisen to ride the TZ750 four at several different circuits in the UK, and its turned out to be a user-friendly bike with much to offer, particularly on the wide open circuits like Donington and Snetterton where all those horses can be unleashed and used to the full.
Multi cylinder madness
The roots of the TZ750 can be traced back to the 1960s, when Japanese manufacturer Yamaha were doing battle with Honda and Suzuki on the GP circuits of the world, all engaged in a desperate battle for racetrack supremacy.
Each Japanese company had chosen to compete in Grand Prix racing around the world to make a name for their relatively young motorcycle factories, plus sell road bikes on the strength of those track reputations for speed.
Whilst Honda chose the high revving, multi cylinder four stroke, in 4, 5 and 6 cylinder formats, Yamaha went for two strokes, mainly twins, but also produced a superb liquid cooled, V4 250cc racer, which scored many a win in the mid 60s. But speeds rose rapidly, with engines making way too much power for the chassis and tyres of the time. Good riders died, or were badly hurt racing 140 -150mph 250, 350 and 500cc racebikes. By 1967, the FIM told all factories to go back to racing twins at 125/250/350cc level after the `68 season – the `add more cylinders game was over.
Yamaha did just that from 1969 onwards, using lower tech, air cooled twins in the 250cc and 350cc class, very successfully too – though they were helped by Honda and Suzuki’s official withdrawl from GP road racing obviously.
But Yamaha’s old sparring partner Suzuki were still fiercely competitive in two stroke road racing against Yamaha, and in 1972 they stunned the world at Daytona with 750cc, three cylinder, liquid cooled race machines, with engines developed from the lard-arse GT750 roadbike, which were entered in the high profile Daytona `200 miler event.
As it turned out, the 100bhp Suzuki `flexi-flyers all broke down during the race, mainly due to chewing up their rear tyres. Meanwhile, Don Emde went on to win the Daytona 200 race – on a 350 Yamaha twin!
The superbike seventies
Sweet deal for Don, but Yamaha knew it had to do something in the big capacity two stroke road racing class to maintain prestige as it was only a matter of time before Suzuki and Kawasaki (who had a fast, but erratically reliable, air-cooled, three cylinder 750 in the running) began to dominate the fledgling Formula 750 class.
So later in 1972 Yamaha built their first F750 prototype, which was actually a 700cc, four cylinder machine. Ace tuner, and ex 250cc World Champion, Kel Carruthers, was invited to ride the bike in Japan the following year and estimated that power output was probably about 90bhp, or as he put it; ’Quite conservative – they could easily have got more from it.’
Kel wasn’t joking either, as the old V4 250cc Yamaha GP bikes of 1966-67 were estimated to be making about 75bhp, so a 700cc, two stroke four could probably have pumped out about twice that amount with a serious development programme.
Basically the new 700cc, across-the-frame, four cylinder unit was constructed from two of Yamaha’s new, liquid cooled, TZ350 engine designs, with the split crankshaft being a little nod back to Yamaha’s 60’s racing heritage – the first V4 250 had a split crank too. The crankcase itself was of ultra-lightweight magnesium construction, with the crankshaft having blanked off ends to keep the engine as narrow as possible.
This meant that the primary drive was taken from straight cut gear cogs from the middle of the twin crankshafts. A massive, very rattly, dry clutch sat on the right of the engine, along with three out of the four exhaust pipes. Barrels were similar to the reed valve induction, TZ350 racer, featuring identical bore and stroke measurements, with a compact water radiator tacked onto the front to keep the upper cylinders at the engines optimum 85 degrees Celsius temperature.
A spindly, tubular steel frame held the engine, with unbelievably narrow (by modern standards) telescopic forks at the front and conventional twin shocks at the rear. Carruthers and other test riders fouind the bike wildly unstable at high speeds – unless ridden hard in a totally straight line. The legend goes that some riders – top class guys in the 70s – simply refused to ride the TZ700, as it was too scary for them.
So the swingarm was lengthened during the development year of 1973 to give the TZ700 a fighting chance of staying on the tarmac once the throttle was wide open. Later, TZ750 models ( also known as OW31s ) had vastly improved monoshock rear suspension, with a cantilevered swingarm to improve handling.
Technically, the TZ700 wasn’t that daring and its interesting to speculate whether Yamaha secretly toyed with the idea of having another Vee four two stroke, or a square format 2 stroke (which is of course what Suzuki did a few years later, with Kawasaki following suit) to contest the 500cc GP class.
Maybe the in-line four cylinder TZ700 was simply cheap, and fairly easy, for Yamaha’s race shop in Japan to produce? Given that some groundwork had almost certainly been laid, on water cooling their existing 250cc and 350cc race bikes, this seems likely. Then again, a V4 750cc two stroke would have ate either its crankshafts, or its1970s skinny tyres faster than Barry Sheene pulled birds. Even in an era that saw the Kawasaki launch the 18 miles-per-gallon, 125mph, KH750 two stroke – for the road – that would have been total insanity.
Who’s your daddy?
In any case, the relatively low tech TZ700/750 machine worked well – in fact, it turned out to work better than Yamaha’s race engineers could have dreamed possible, creating a template for a new generation of big, fearsomely fast, two stroke racers.
Yamaha’s ’beast of a racer’ ultimately spawned mad things like the NS500 triple Honda, the YZR500 V4 500 Yamaha, Schwantzs RGV500 Suzuki and the `big bang NSR500 Honda that probably turned Mick Doohan’s hair grey in one season.
Until the TZ750 came along, plenty of people in motorcycle racing simply didn’t believe a big capacity 2 stroke could ever challenge the multi cylinder MV Agustas, or Hondas (Dick Mann took the 1970 Daytona 200 win on a CB750 racer) because the strokers were too fragile. But the big TZ proved to be the Ford Escort of big bike racing – club racers and world champions could all buy, and tune-up, an off-the-shelf race winner.
Yes, the TZ750 was brutal, a bit crudely engineered, hard to handle on tight turns. But it just kept winning F750, Superbike and Daytona races for the best part of a decade after its first appearance. Not too bad for a jumped up lawnmower engine.
Get Yamaha motorcycle insurance for the yamaha tz750.
|ENGINE||In line, two stroke, four cylinder, liquid cooled|
|BORE AND STROKE||66mm x 54mm|
|CARBS||X4 34mm Mikuni|
|ESTIMATED PEAK POWER||140bhp|
|CHASSIS||Steel tubular cradle type|
|FRONT FORKS||Varied according to team spec|
|REAR SUSPENSION||Yamaha monoshock, cantilever swingarm (1975 onwards)|
|WHEELBASE||To team spec|
|WHEELS/TYRES||18 inch wheels, 3.25 section front, 3.50 section rear|
|BRAKES||Twin 300mm front discs, single 220mm rear|
|TOP SPEED||Estimated top speed; 180mph (depending on gear ratios)|
|BUYING INFO||About 600 TZ750s produced 1974-80, used examples from £5,000 upwards depending on condition and history.|
|COLOURS||Factory yellow/black, otherwise team choice|