Oval pistons: The Honda NR (New Racing)

[Motofool]

Copied from
http://en.wikipedia.org/wiki/Honda_NR

"The Honda NR (New Racing) was a V-four motorcycle engine series started by Honda in 1979 with the 500cc NR500 Grand Prix racer that used oval pistons. This was followed during the 1980s by a 750cc endurance racer version known as the NR750.

The oval piston concept allowed for eight valves per cylinder which generated more power due to the increased air/fuel mixture throughput and compression.

In 1992 Honda produced around 300 street versions of a 750cc model, the NR (often mistakenly referred to as the NR750), with a 90-degree V angle. Whereas the NR500 had used an oval piston with straight sides, the road going NR750 used an elliptical piston with curved long sides.

The bike became the most expensive production bike at the time when it was selling for $50,000 and with the rarity, nowadays they rarely change hands."

[Racer x]

The NR stood for never ran.

[Rifleman]

I've got to assume ring fabrication had to be a bugger. seems round pistons do what needs to be done... Wankle engines are the only other "different piston design" that makes sense... instead of stopping the piston, reversing it's direction 180' and then moving it again... the rotor piston keeps going it the same direction.

just difficult to keep a seal between the lobe and the cylinder and the side wipers.

this just seems to be added technical stuff to over come for ... well for a ? in performance upgrade is all.

[Flying]

Looks absolutely terrifying to perform maintenance on.

[alex.s]

Originally Posted by Rifleman

I've got to assume ring fabrication had to be a bugger.

wouldn't they both be stamped the same way? just with a different die shape?

[MrAtom]

I want star shaped pistons. And then smiley faced pistons! In fact, I want all the shapes of pistons that a playdoh spaghetti maker could make!

["A"]

Dropped $60k NR750.

[ducatiman]

Ultra rare, quite impressive machine in the flesh, prominently showcased by US Honda at Daytona, 2010

[Rifleman]

Originally Posted by alex.s

wouldn't they both be stamped the same way? just with a different die shape?

I don't think so, I'm pretty sure they are spring steel and are formed in one continuous circle and then cut into a single ring. Heat treated, tempered and hardened... I've put new ones in, never seen them made. But that's how I'd make them a lot less waste that way.

but the rings are supposed to press out against the cylinder wall. I have a ring compressor that squeezes them into the piston groves so the piston can be fit into the cylinder. I'm just one guy with no degree in mech e... but it would seem to be insanely difficult to make a ring that presses out against the oval cylinder wall equally or efficiently. The circle works, that flat spot in the oval, seems to me to be the place that the ring would be pressed against the cylinder the softest/least

I've read some stuff by Motoman... and it seem from his stand point, rings sealing is #1, #3, and #4 on the important things an engine must do. HIs break in on a rebuild engine flies in the face of everyone else, but it is designed to seat the rings, max seal, max compression, max horse power for the fuel burned.

his ideas make sense, maybe i'm being taken for a ride. Interesting concept, dual rods looks robust...

if it was a major advancement... It would be in the bikes today.

[alex.s]

Originally Posted by Rifleman

Heat treated, tempered and hardened

i believe you mean relaxed, hardened, then tempered.

[Motofool]

Originally Posted by Rifleman

........... it would seem to be insanely difficult to make a ring that presses out against the oval cylinder wall equally or efficiently. The circle works, that flat spot in the oval, seems to me to be the place that the ring would be pressed against the cylinder the softest/least................

Copied from
http://world.honda.com/history/chall...ine/index.html

"The piston ring, also, was a real headache, since the oval shape was so difficult to machine accurately. Experiments were repeated over and over, through a process of trial and error. For example, they tested a split-type ring made of two parts and formed the ring into a "walking stick" shape. But after every conceivable alternative had been tried, they found themselves back at the starting point with a conventional, self-stretching piston ring. Even with that configuration they still had to expend extra effort calculating the appropriate dimensions, so that the ring would remain in free form during machining, but produce constant bearing pressure once installed. NC machines were still inaccurate during that period. Therefore, additional effort was required to produce the desired quality of a part by accurately reflecting the specified machining dimensions."

[Rifleman]

Originally Posted by Motofool

Copied from
http://world.honda.com/history/chall...ine/index.html

"The piston ring, also, was a real headache, since the oval shape was so difficult to machine accurately. Experiments were repeated over and over, through a process of trial and error. For example, they tested a split-type ring made of two parts and formed the ring into a "walking stick" shape. But after every conceivable alternative had been tried, they found themselves back at the starting point with a conventional, self-stretching piston ring. Even with that configuration they still had to expend extra effort calculating the appropriate dimensions, so that the ring would remain in free form during machining, but produce constant bearing pressure once installed. NC machines were still inaccurate during that period. Therefore, additional effort was required to produce the desired quality of a part by accurately reflecting the specified machining dimensions."

jeeze, I keep pulling stuff like that out ma ass and my head will swell so bad I won't be able to put my helmet on. (ba dump bump)

Originally Posted by alex.s

i believe you mean relaxed, hardened, then tempered.

yes

[Motofool]

"Reminders of the many trials involved in NR500 development have found a place in the hearts and memories of everyone involved. Until recently, in fact, a drawer in Yoshimura's desk contained damaged connecting rods and broken valves, which came from assemblies that fell apart during early bench tests.

"Every time I saw those parts," Yoshimura recalled, "they reminded me of the enthusiasm we had during development. They reminded me of a hotel in Nasu in the dead of winter, where we wrapped ourselves in blankets as we drew layouts because the heater wasn't working. I remember our excitement at finally having completed the drawings. Of course, they also brought back bitter memories from those races."

From its comeback in World Grand Prix with four-stroke engines to the creation of oval piston engines, Honda continued setting high goals and fostering the spirit of challenge in every aspect of development. The wealth of new technologies now possessed by the company is in no small part a result of these efforts.

"To create anything, you must put your heart and soul to it," said Yoshimura, in nostalgic reflection on those days. "The development of oval piston engines impressed that upon me, as well as on the other young engineers.""