[Technique] Honda's Twin Crankshaft NSR250

Hello,

I would love to discuss with those than worked on or have pictures of Honda's twin counter rotating crankshaft NSR250 engine. How good was that engine? What did Honda stop going in that direction? From my understanding, it was a reed valve engine similar to Aprilia's disk valve design. Merits and disadvanteges vs the twin crank disk valve design?

Frits? Jan? the floor is all yours to enlighten me:)

Here is a link to the model I'm looking for information on:
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Thank you, Riley. You may start the music now .
Probable someone at Honda believed that the Aprilia's counter-rotatings crankshafts were an advantage regarding gyroscopic effects on handling. Personally Jan Thiel and I would have preferred to design an Aprilia
V-250 with one crankshaft.....
Anyhow, Honda copied the twin cranks, but not the disk valve inlet system. Then they gave this machine the two side-mounted radiators that hat already proven themselves in the NeverReady NR500 as insufficient.
The result was the worst works racer they had built in years; down on power but high on water temp. Privateers on Honda RS250 production racers were occasionally faster...

Frits,

Thank you for the reply. Wasn't it the TSR with the side rads? The pic in the link shows conventional radiators. I was under the impression that this engine was very powerful but too expensive for Honda to produce as an RS racer????? Didn't Kato win the Championship with this bike in "MovieStar" colors?

I'm not sure but I seem to recall that Roberto Rolfo raced the twin-crank Honda and that Kato later rode its successor, with one crankshaft.
The twin-crank machine definitely had side radiators. When these proved unsatisfactory, they were replaced with conventional rads, but that did not iron out all the built-in mistakes

Frits,
I apologize for pressing the issue, but the bike that Kato won the 2001 world championships is the engine in question for me. Exhaust out the tail section and the lower cylinder is left of the swing arm. For sure this bike must have had a good engine to dethrone Aprilia!

In the 2001 Mugello race, Kato went 2.8 kph faster than the next rider. In the various practice and QP rounds the Aprilias were upto 3kph faster.

Did this engine fire in tandem? I believe the cylinder angle was greater than 90 degrees vs each other?


Riley

Hi Riley,
I think you have the last version of the twin-crank, which was much improved. The first version appeared in... 1999? and was meant to make better use of unleaded
fuel. It had the twin radiators mentioned by Frits, and also a "pivotless frame": the swingarm pivoted directly in the crankcases and not the frame, like the 954
fireblade.

The bike was slower than a kitted RS, and much slower than a kitted RS motor in a TSR frame with twin-sided swingarm. Aprilia won the title in 1999.
Tech 3, who raced the bikes that year with Olivier Jacque, abandoned ship for Yamaha in 2000, with Jacque & Nakano running 1-2.

The twin radiators disappeared early. The pivotless frame was ditched at the end of '99 and replaced with the one in your photo, which Katoh rode
to 3rd in 2000 and won the title in 2001. By then it was starting to produce decent horsepower, but still little more than an RS kit and less than the Aprilia.
After Katoh's title, Honda announced there would be no more NSR250's, their remaining years in 250 were with what might be called "AA"-kitted RS's.
Basically, Honda screwed up big time then went off to sulk and wait for the 4-strokes to arrive.

Riley Will a écrit:

Frits, I apologize for pressing the issue, but the bike that Kato won the 2001 world championships is the engine in question for me.... For sure this bike must have had a good engine to dethrone Aprilia! ....Did this engine fire in tandem? I believe the cylinder angle was greater than 90 degrees vs each other?

What this bike had, was a good rider! Kato was in a class of his own then. I cannot comment on the V-angle; Honda did not exactly invite me in... What I do know, is that after a race Kato's rear tyre looked like new while the Aprilia's rear rubber was binnable; Honda seemed to have a perfect working traction control.

One good consequence of the poor performing 1999 bike was that it allowed some interesting privateer teams to show themselves:
notably Jeremy McWilliams with the team from Queen's Uni Belfast.

Pictures with lateral radiator:
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The last 250 championship winner was a Honda Two stroke

Dave Pearce a écrit:

The last 250 championship winner was a Honda Two stroke

Thanks to all those Aprilia works riders who drove each other off the track during that season .
I did no so much mind Aprilia loosing; I did mind Honda winning .