The Unseen Achievement of Honda's Oval Piston Engine - A different perspective on the Honda NR story

The Unseen Achievement of Honda's Oval Piston Engine - A different perspective on the Honda NR story

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Let me ask you a question. Which of these shapes  is the best shape for sealing something? And it doesn't matter what you're sealing; water,  air, oil, combustion, coolant. Doesn't matter   Which shape seals the best? What do you think ? Well while you think about the answer I'll get the advertising portion of the video  out of the way by telling you that today's   video has been brought to you by Surfshark. Now  Surfshark is a virtual private network aka VPN meaning that it makes it very difficult for internet  service providers and pretty much anyone else to   track and control what you do online. Well, okay but  why would you care your internet is fine as it is right? Well, yeah but remember that show on Netflix  that you always wanted to watch but you can't   because you don't live in the "right" country? Well  Surfshark can virtually place you in more than 90   different countries worldwide, meaning that there's  no streaming library content that you can't  watch anymore Or maybe a website is blocking  you because of your location? Not with Surfshark   Or maybe you're traveling and want to have  access to content and perks available exclusively in your home country? Not a problem with Surfshark. Or maybe you're just tired of horrible personalized ads and cookie constant pop-ups? Well,  Surfshark gets rid of those as well and it does   so much more for your online security and privacy . And here's the good part: you can get it for 83% off  

If you follow the link down in the description  and use DRIVING4ANSWERS as your promo code   This is going to get you three additional months  of Surfshark for free plus additional 27 months for free of powerful anti-virus protection. If that's  not a good deal then I don't know what is Okay, now back to our question. Which shape is the best for  sealing? Well it's a circle. Why is it a circle? Well that's because a circle is the simplest and most  uniform shape of all and chances are very high   that wherever you need to seal something you're  gonna find a circle in the design and this is why   pistons have been circular pretty much since  day one and will likely continue to be circular   in the future. And this is why all non-circular  attempts at internal combustion have ultimately   failed to either enter or stay in the mainstream.  They may have produced some truly admirable   engines but they were more complex and expensive  to produce without offering any justifiable   benefits over the traditional circular  piston design. Now here's another question  

If I know that a circular shape is best for  sealing then certainly Honda's engineers know that as well And if there's a century of circular  piston engines clearly demonstrating that the design works Then why would someone  invest an incredible amount of time, money and human resources to try and reinvent the  wheel by developing an oval piston engine  If it seems pretty likely that the design is going to  ultimately fail. Well to answer that question we   have to process a cocktail of history, mechanics  and human persistence. Let's start with history Now the year is 1960 and Honda started an  ambitious campaign to try and dominate the   world of motorcycle racing, and indeed in a matter  of just a few years they started winning races   left and right with their motorcycles equipped  with four stroke engines. But by the mid-60s most  

other manufacturers and racing teams jumped onto  the bandwagon of switching to two-stroke engines   Now this decision really was a no-brainer  at the time because at least in theory   a two-stroke engine enables twice the power at  half the weight because with a two-stroke you   don't need camshafts, valves, and lifters and big  complicated cylinder heads to house all of this   And you don't need chains or belts to drive the  camshafts and the only penalty you really pay with   a two-stroke is increased emissions and reduced  fuel efficiency but we're talking about racing in   the 60s here and emissions and efficiency really  weren't on the list of priorities. But despite the   two-stroke trend Honda remained faithful to  four-stroke engines. Founder Soichiro Honda   is famous for disliking two-stroke engines.  A sentiment he spread throughout the company  

But Honda did more than just remain faithful. They  kept trailblazing and pushing forward in the field,   and by 1966 they did what no other manufacturer  did before, and that is to score podiums in every   single one of the five different classes of the  world motorcycle grand prix. This bike the RC166   perhaps best exemplifies how far Honda managed  to push the four-stroke engine. This bike raced   in the 250 cc class back in 66 when it was piloted  by legend Mike Hailwwod. Inside the bike is a inline  

six-cylinder engine with only 250 cc of  displacement, with four camshafts and 24 valves and it revved to almost 20.000 rpm. To make  this possible, this degree of miniaturization in an   age before CAD software and CNC machines required  incredible persistence, dedication and precision So in 1966 Honda proved their point. Their  four-stroke engines were amazing, reliable,   they featured clockwork precision. But most importantly  they could beat equivalent two-stroke engines So in 1967, with nothing left to prove Honda retired  from the world of Motorcycle Grand Prix racing and   instead decided to shift its focus on developing  mass-produced cars. Instead of chasing power  

you know, and performance Honda was now chasing  environmental responsibility and fuel economy   And in 1973 they released the CVCC equipped Honda  Civic, making Honda the first ever manufacturer to   release a car in full compliance of the clean air  act passed by the U.S congress. But this shift to   cars came at a price, and the price was paid by  motorcycles. Two-thirds of the staff working in   the motorcycle division were transferred to now work  on cars. Although Honda did release some important and   iconic and prominent motorcycles throughout  the 70s, these bikes were based on technology   back from the 60s. There was no innovation. Of  course, the reduction in personnel played a part   in this but the main reason behind the lack of  innovation was that Honda was no longer racing   Without racing there is no drive to create new  technology to beat the competition. Without racing   there is no suitable environment where you can  test this new technology. By 1977 Honda realized  

where this would end. Honda would end up lagging  behind other manufacturers in terms of technology   and innovation. So in the same year, exactly  a decade after they had left the world of   motorcycle grand prix racing, Honda announced their  return. But things had changed during their absence   Two-stroke engines had advanced dramatically  and they were now the norm in motorcycle racing   In fact back in 77 the rules also did not favor  four strokes. There was no displacement advantage   for four strokes and the rules simply stated that  the maximum allowed number of cylinders was four   and the maximum capacity was 500 cc, and this was  the same for both four strokes and two strokes Now when a piston travels from top to bottom or vice  versa that's one stroke and as the name implies   a two stroke needs only two strokes to complete a  full combustion cycle, whereas a four stroke needs   four strokes to complete a full combustion cycle.  Intake, compression, power/combustion and exhaust all occur separately and independently  in a four-stroke engine. While the design of  

the two-stroke allows it to complete intake and compression and power and exhaust pretty much   simultaneously. This means that in a two-stroke  engine whenever the piston is at the top the spark   plug fires and combustion occurs. In a four-stroke  combustion occurs only every other time when the   piston is at the top. This means that a two-stroke  engine achieves twice as many power strokes at the   same rpm, meaning that it can achieve more power and  generate more output and performance from the   same displacement and at the same rpm compared to  a four-stroke engine. Despite these advantages of   the two-stroke Honda once again decided to remain  faithful to four strokes and try to beat the   competition on an uneven playing field right after  coming out of a decade along hibernation So they started putting together a team to work on the NR project. NR being "new racing". Now Honda's   goal was also to foster innovative thinking, and  you know new talents, which would act as key people   in the future. So many of the 100 members of the  NR project were actually recent college graduates  

So the NR team got to thinking and of course  very quickly they figured out that if you want   to beat a two-stroke with a four-stroke of equal  displacement then you need to rev twice as high   if you can't make the same torque at the same  rpm because you're doing half the power strokes   then you need to rev twice as high in order to  generate the same power output. Most two strokes of   the time were revving to around 10 - 12.000 rpm  and they made peak power there so Honda decided   that their four-stroke had to rev to 23.000 rpm  in order to generate a competitive power output  

of 130 horsepower. Now to rev to this ridiculous  rpm you have to make it possible for the engine   to take in and push out massive amounts of air  very very quickly. Now to increase the breathing   capacity of the engine there's many things you can  do. One of the first things most engineers would do   is increase the size of the intake and the exhaust  valves. But this has a limit, because eventually you   run out of combustion chamber space and you have  to increase the bore in order to increase the size   of the combustion chamber. But increasing the  bore means increasing the displacement and that's   something Honda couldn't do. But fortunately  for Honda the world motorcycle grand prix  

rulebook only said 500 cc and four cylinders  without explicitly defining what they meant by cylinder Probably because they never expected  anyone to be crazy enough to make anything other   than a round engine cylinder. But Honda was crazy  enough to pursue a non-cylindrical cylinder   So they came up with this: if the cylinder was oval  instead of round that they could fit more valves   into it and sustain the airflow needed to generate  23 000 rpm. Of course an oval piston is something   no one had ever attempted before and so Honda  found itself in completely uncharted territory   Chasing a dream of a V4 engine with four oval  pistons and 32 valves all packed into only 500cc of displacement Of course the novel approach  meant that more issues and problems appeared   during the prototyping and development stage then  it was possible to count. Toshimitsu Yoshimura, an   engineer involved in the NR project remembers  it like this, he said: "When i look back at it   i'm not sure if we were experimenting with cutting  edge technologies or obsessed with foolish ideas   The engine faced two main obstacles. The first one  was the piston rings. Remember, a circle is the best  

shape for sealing. This is also because a circle is  relatively easy to machine accurately. So machining   oval piston rings proved to be the ultimate  machining nightmare for Honda. Initially they   experimented with what they called a "walking stick"  style piston ring. This was essentially a split   piece piston ring, each piece consisting of a shape  which look like a walking stick. Now after a lot   of experimentation and trial and error and effort  and time and money they had to abandon this design   It simply didn't work. So they returned to the, you  know, traditional single piece piston ring and then   this too needed a lot of experimentation and trial  and error until sufficient machining accuracy was achieved The second major obstacle were the rods  and the piston pin. A circle is also best for  

sealing because a circle moves in a relatively  uniform way and its movement is easy to control   The elongated shape of the piston meant that it  was more susceptible to rocking and wobbling in   the cylinder meaning that it needed two connecting  rods to control its movement and stabilize it But of course an elongated piston together with two  rods required a very long piston pin to put it all   together. Now at high rpms, when the complex forces  acting on engine internals would get high enough   this caused the long piston pin to flex and  break everything and this is because of course   it's impossible to keep a piston perfectly  level in the cylinder and it's impossible to   prevent the crankshaft from flexing a bit. This  means that the two connecting rods don't move   in a perfectly equal manner which leads to the  piston pin flexing, putting strain on everything   and breaking everything. But after more endless  experimentation and trial and error sustained by   incredible persistence Honda's engineers managed  to overcome all of these development obstacles one by one   And the first race-ready NR500 motorcycle  rolled out onto the racetrack in August of 1979 to race at the British grand prix  held at Silverstone. But the debut   was a debacle. Two bikes were entered into the race  and they barely managed to qualify. Once they did,

the first bike crashed at the very first corner  after the engine spilled oil onto the rear tire   The second bike had to retire after only seven  laps due to ignition problems while running second last Mick Grant, my goodness it's Mick Grant on the  Honda. A bitterly bitterly disappointed Mick Grant   who fortunately looks all right and the new honda  v4 of Mick Grant who has done so much in Japan to   get that machine going for this race is out of the  race on the very first lap. This embarrassing debut   made it obvious that even incredible persistence  has its limits and that the oval piston technology   still had a long way to go. The engine could not  yet rev to 23.000 rpm and it barely managed to   scratch the 110 horsepower mark which was way off  the target of 130 horsepower. But Honda's engineers   didn't give up. They took the blows, learned from  their mistakes, and by 1982 they managed 19.500 rpm   and 135 horsepower which was a pretty admirable  result but the bike still wasn't winning any races   it was still not competitive. Why? Well because a  V4 engine with eight connecting rods, eight spark plugs

32 valves big oval pistons and big oval  cylinder heads wasn't just incredibly complex   it was also 20 kilograms heavier than any of the  competitor engines, and it wasn't just heavier the bulky complex shape put the weight in the wrong  place negatively affecting the center of gravity   and the overall balance of the bike. The best  result the NR500 ever achieved was when rider Freddie Spencer in 1981 managed to briefly hold  fifth place before the bike broke down. By 1982   Honda finally caved to pressure from shareholders  fans and pretty much anyone else and developed   a two-stroke bike, the NS500 to race alongside  the NR500. Pretty soon the NS500 made the    NR500 look very slow and very silly and already in  1983 again piloted by the same person the NS500   won the world motorcycle grand prix. the NR500  was retired in the same year without ever winning   a single grand prix race. It never even came  close to doing that which it was designed for  

So what is the rational conclusion to all  of this? I think it's something like this:   Don't waste time and money trying to reinvent the  wheel. The circular piston works and there's a very   long track record to prove it. Therefore trying  to do something different is a waste of resources   The oval piston engine is an abject failure  because it didn't even come close to achieving   its goal of becoming a grand prix champion.  Right, this is the most rational conclusion?  Actually no this would be a little more than a  very short-sighted and naive conclusion. The real   conclusion is this: Failure is not the opposite of  success and the NR made immeasurable contributions   to motorcycle technology. Wait, what? How did it  contribute anything if the oval piston design has  

been abandoned and never used since? Well by trying  to make the impossible possible Honda's engineers   experimented with and trailblazed numerous new  technologies most of which are used in motorcycles   to this day. For example, they experimented with  and successfully employed magnesium and titanium   alloys to reduce weight. This was a first and  something that everybody in the competition of   the motorcycle grand prix quickly copied. They  also developed, improved and perfected numerous   new machining techniques and helped advance  numerically controlled machining which made it   possible to machine more complex and different  shapes. They also had to deal with aggressive   engine braking and to do that they developed a  back torque limiter, it's something most bikes have   on them today we just call it different. We call  it a slipper clutch. And many other technological   advancements made during the development of the  NR and the oval piston engine later made their way   to other motorcycles and are used to this day. But  the oval piston story did not end in 1983 because  

in 1992 honda released the NR a motorcycle which  proudly wore the name and featured the technology   of a racing bike that won nothing. With a 750cc  oval piston engine churning out 125 horsepower   at 14.000 rpm and a dry weight of 223 kilograms  it was just like the bike which inspired it Not as fast as the competition but dramatically more  complex and expensive. At 50.000 dollars  

which is 105.000 dollars in today's money it  was the most expensive motorcycle off its day   But even though it had no racing successes to  celebrate Honda made 200 NR motorcycles as the   definitive statement and proof of dedication and  perseverance as if to say "We're the only ones   capable of making this absurd technology work  and we even managed to perfect it to the point   where we can mass produce it" Honda learned  many valuable lessons from its failure They were proud of it and they wanted to show all of  their achievements in one bike to the whole world   Now an interesting little fact, the race  version the NR500 had pistons with flat sides   The road going version, the NR, had oval sides in  an effort to bring the shape of the piston that   bit more closer to circular in an effort  to ease manufacture and improve sealing   So the final conclusion is that a failure  is not a failure as long as you learn from it Look at any successful individual anyone from a  business person to an athlete or anyone in between   And you will see that they carry the  valuable experiences of many many failures  under their belts. The same holds true for  building engines, winning races or pursuing any other goal Be ready to fail but also be ready  to learn and grow from it and if you're able to do   that then success is just a matter of time. And  in 2002 when moto gp rules changed once again   this time to favor four strokes, a technology whose  improved efficiency and reduced emissions gave it   a brighter future, Honda would once again prove  that they weren't afraid to go against the grain   and take the risk of stepping into the unknown.  They developed a V-engine with an odd number of cylinder A V5. A completely unprecedented design  which in the hands of legend Valentino Rossi  

obliterated the competition. By the way I have  a video on the V5 which explains how it works   it's super super boring. Yeah that's pretty much  it for today, I hope you enjoyed that. As always   thanks a lot for watching and I'll be seeing you soon  with more fun and useful stuff on the d4a channel

2022-09-12 13:32

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