TZ750 & YZR500 - Track Monsters from YAMAHA

"They don’t pay me enough to ride that thing." said Kenny Roberts after winning a race with a bike which beat the Harley-Davidson’s XR750 considered as King of the Oval track. That particular bike is the YAMAHA TZ750. Well, Yamaha as well as Kawasaki is known to produce bikes which are almost street illegal, so when they produce actual bikes where they are allowed to push the envelope to no limits, imagine how their performance frenzy engineers smile quotient might be! And when they are allowed to do that, they produce bikes like the TZ750 and YZR500. Both these bikes are of course not very common in forums and web world as they were not street legal and so the audience catering to this class is also less. But these are the bikes from which the companies make the Sports and Super Sports models. These are models we should know about.
The TZ750 two-stroke, four-cylinder liquid cooled motor was actually a road-racer that Roberts used to ride and of course win and then they put it in a dirt-track frame and increased the power to 125 horsepower. Well, that’s it. But there was one problem, how do you ride a 2 stroker with 125 bhp? Good question! Well, that onus fell on Mr. Roberts too and he found the power a little too much to handle. Roberts was always riding the 2 cylinder Yamahas with around 80 bhp, so suddenly, this was a bit too much.

But this was a weapon made by Yamaha to beat the increasing dominance of HD through their XR750. And so, in 1975, Roberts rode this TZ750 dirt-tracker at the famous Indy Mile dirt-track oval, winning the race ahead of Jay Springsteen and 2 others on their XR750. With the bike capable of hitting 240kmph, AMA thought that it was outright dangerous to have a bike like this and so new rules were set and the TZ750 was banned. Such a short history. Participated in only one race, won and banned.
This thing had to be scary. Now think for a minute, a Yamaha, that too, a 2 stroker, no worries for heating, it is liquid cooled, again that too with 4 cylinders belting out a whooping 120 bhp, which was later increased to 140 bhp from a 2 stroker!!! Think about this. These bikes are not street legal because it usually has too much power. But the TZ750 was banned… even from racing!!!
But luckily it was only the oval track. For in road racing, it almost dominated the 70s winning races everywhere including the Daytona 200, which it won nine times in a row starting from 1974.

To start off from the beginning, what Yamaha actually did was graft two 350 cc twin race engines and together they belted out 90 bhp from the crank with bore/stroke ratio was 64mm x 54mm. These twins were the TZ350. The crankcase itself was of ultra-lightweight magnesium construction, with the crankshaft having blanked off ends to keep the engine as narrow as possible. The primary drive was taken from straight cut gear cogs from the middle of the twin crankshafts. A massive dry clutch sat along with three of the exhaust pipes on the right of the engine. A spindly, tubular steel frame held the engine, with narrow telescopic forks at the front and conventional twin shocks at the rear. Later, TZ750 models (also known as OW31s) had vastly improved monoshock rear suspension, with a cantilevered swingarm to improve handling. It was named F750 as a prototype although it was actuallt 700cc. Awesome! 90 bhp from a 2 stroker would shred any kind of race tire way back then. Kel Carruthers, the1969 250 world champ was the first man who tested the bike. He removed the initial glitches by increasing the swingarm and improving the suspension. Still except for Kenny, the others were quite slow on the tracks as they were not able to handle it as the bike had small fork tube and chassis. After about 3-4 races, Yamaha added some more power! Another 20 bhp. Why? Because according to Kel, "It wasn't as fast as it could have been. They were really conservative in the way they built it.” In a way, Kel was actually serious. You know Yamaha back in the late 60s had V4 250cc GP bikes which were making around 75bhp, so logically the bike should have around 140bhp. Of course there was no chasis or tyre which would have hold it was another thing, but come to think about it, the bike with modifications later did belt was that much power.

The original bike which got banned by AMA is currently with historian Steve Wright and was on display at the Motorcycle Hall of Fame Museum at AMA headquarters in Pickerington, Ohio. There is something to turn you green with envy also. Yamaha sold around 600 of these mean machines over the counter between 1974 to 1980. Sorry, you won’t get one now or for the matter none of those 600 dudes are selling it. Nope ebay won’t be helpful, I tried. But there is one genuine TZ750 which is street legal. A certain Joe Taormina had sufficient patience to complete the task of converting this wild beast into a street, of course not before countless legal hassles with the transport department. Taormina is a mechanic at Yamaha Motors of Pacific Beach near San Diego, which helped him largely. The list of street-legal requirements are an electrical system, complete with a battery and charging system, a brake light which would operate with a dead engine, turn signals, mirror and a horn. A headlight surprisingly is not required but was included in his plans. With additions from other Yamaha models for these things, he finally got his street legal TZ750.Those who have ridden the original TZ750 mentions about the amount of low-end torque available. And the feeling of letting the clutch go is something similar to getting launched from an aircraft carrier. “The cars around you that were doing 55 mph seem to have suddenly stopped and parked. Those cars that were ahead, out of sight, are suddenly right here.”
We, the less privileged ones can only imagine.
Engine - 748cc, liquid cooled, two stroke, In line, four cylinder,
Bore and Stroke - 66mm x 54mm
Transmission - 6 speed
Carbs – 4(Four) 34mm Mikuni
Estimated peak power - 140bhp
Chassis Steel - Tubular cradle type
Rear suspension - (from 1975) Yamaha monoshock, cantilever swingarm
Front forks & Wheelbase - Varied according to team spec
Brakes - Twin 300mm front discs, single 220mm rear
Estimated Top speed - 180mph (depending on gear ratios)

And now coming into the YZR500 which is…what to say… a monster that would eat the TZ750 for breakfast. Just to get the hang of it, the first YZR500 model came in 1973 with 80bhp with maximum rpm of 10,000 which went upto… now you need to hold on to something… 180bhp for the 1996 model with a max rpm of 12,500! The reason for this is largely the results of Yamaha engineers' efforts to improve the "Kadenacy effect" through measures like the YPVS and many other discussed below.
(Source – Wiki: In a two-stroke engine the pressure-drop resulting from the Kadenacy effect assists the flow of a fresh charge of air, or fuel-air mixture, into the cylinder. However, the Kadenacy effect alone is not sufficient and must be boosted in some way. In small engines this is done by crankcase compression and, in large engines, by the use of a Roots blower.)
Yes a 2 stroke beast with 180bhp. Yes, it’s a race version, but nonetheless, just think how you will feel atop it!
The importance of this bike in the history of Yamaha’s sports motorcycle cannot be summarized nor stated in a blog.
In 1973, Yamaha broke the MV Agusta domination in the World GP series when the YZR500 won its first race in April at the French GP and know what, it was the bike debut. Then in 1974, Yamaha won the manufacturers championship. The date was April 22, 1973, and the place was the opening round of the GP series at the Paul Ricard circuit in France. For Yamaha this race was its first ever in the 500cc class. Jarno Saarinen of Finland drove to victory on the YZR500 over the 20-lap 116.2 km course in less than 46 mins beating Phil Read on the MV Agusta four-stroke machine by a full 16-second margin and interestingly Japan's Hideo Kanaya came in third on the YZR500. Then again in the second round of the series in Germany, Saarinen and Kanaya would finish one-two. It clearly marked a new era of dominance in GP racing breaking the invincible MV Agusta run. Well, you can’t say that 2 stroke was clearly proved that in similar capacities, a 4 stroke is just not good enough because brands like HD, Ducati, Norton, BMW, Triumph, all were racing with 2 strokes but they just couldn’t beat MV Agusta. Such was the dominance of MV, that from 1958, they have won all but one (1966 by Honda) of the manufacturers title. The refinement of the 4 stroke engine was too much for any 2 stroke to match.
Still Yamaha was working on double shifts on a secret 2 stroke project (code name OW20), but the sole aim was not the MotoGP circuit. Yamaha was also looking in the U.S market and participating in the Daytona 200 to make a mark in the circuit and thereby to the public market. OW20 was, at that time, just another product since the focus was more on 700cc machines. These 700cc engines were built in die-cast crank case in contrast to the OW20 that was built with a sand-cast crankcase. So simultaneously, Yamaha was working on 2 projects, the first, a 700cc model, the "YZ648" which was the prime model as they were more interested in the Daytona circuit vis-à-vis production market and the second, the 500cc named "YZ648A”.
1972 marked a remarkable year for Yamaha since both its prototypes "OW19" (700cc) and "OW20" (500cc) were almost finished and were running quite well. It was the year of Yamaha’s innovation. Starting from base work like grouping four cylinders into units of 2 to give a much slimmer engine design to fine work like introducing an "idle shaft" between the right and left crank shafts as the drive force shaft, Yamaha was at their height of innovation. Credit and mention of Mr. Takashi Matsui has to be given as he was the chief engineer during that period. Mr. Matsui says "From our experience developing the RD05 (the 1964 250cc GP machine) we learned that the ignition order has a big effect on the idle gear, and so we decided to use a well-balanced firing order in which the two inside cylinders and the two outside cylinders fired at the same time. In our efforts to increase the machine's potential banking angle, we designed triangular cross-section mufflers and grouped all four exhaust pipes together and ran them under the crank cases,"
What resulted was an engine with the width about the same as a V4. The frames were made of new chromium molybdenum steel with a wide-type side rail. Disc brakes were added at front and rear. Yamaha philosophy on innovation has depended more on overall balance, performance and of course handling rather than outright power. And finally YZR500 made its debut in 1973 and the mentioned above factors showed its worth in YZR500 which helped it break the MV dominance. And in 1974, it was evident that Yamaha has taken a serious decision in MotoGP when it signed none other than the great Giacomo Agostini.
Since then till 2003, for 30 years, Yamaha continued to compete in GP with its evolving YZR500 factory machines. In these 30 years, the YZR500 alone won an amassing and very very enviable record of 115 wins through 20 different riders and also winning a total of 11 rider championship titles and 9 manufacturers’ titles. Till 2001, the 500cc class of the World Road Race Championships was competed on two-stroke machines, then in 2002 for one year, it became a mixed two and four-stroke competition and from the 2003 season, the MotoGP class has become a completely four-stroke competition, and thereby bringing to a close the age of the two-stroke 500cc machines.
But the importance of YZR500 can hardly be ever forgotten. It’s a history of technological innovation and constant evolution. The YPVS, the rear-exhaust system, the Deltabox frame, the electronic-control suspension, everything that there is in the R1 can be credited to the YZR500. Ofcourse the street legal version, that’s why is YZF, not YZR! Some of the famous riders who rode it to world championships are Giacomo Agostini (1975), Kenny Roberts (1978, 1979, 1980), Eddie Lawson (1984, 1986, 1988) and Wayne Rainey (1990, 1991, 1992).
To see all the YZR series, visit the official Japanese Yamaha page on YZR500. Read a special section extensive report on the history of Yamaha's YZR in MC NEWS Australia. A brilliant article on the Yamaha TZ750 is available in Motor Cyclist OnLine. You might enjoy a lot of pictures of Yamaha Racing available in Racing Motorcycles.


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