Rotary Engines and Dirtbikes?

[YZ250]

I've been wondering, for those of you who know what a rotary engine is, how come they haven't put them in dirtbikes at all? Theres been a few motorcycles with rotaries but i've never heard of any dirtbikes with them. Today it's all about saving emissions and fuel economy and such, and the rotary engine is perfect for that. It can produce more power than a piston and uses less fuel. If the dirtbike companies wanted to be more eco friendly they could mount a rotary engine in heir dirtbikes, or at least make a prototype, because then you'd have the power of both 4 stroke and the high end of 2 stroke, but you'd also have the fuel economy and emissions of a 4 stroke. All you would have to do is scale the engine down so that it would fit in the chassis, you wouldn't have to worry about the power to size ratio. It all makes sense and seems like a genius idea, so why haven't they done it yet?  

[DangisMX]

You probably mean Wankel engine, as a Rotary engine might refer to a piston engine where the pistons are arranged in a circle like in old aircraft engines, and yet, even these engines were used for a motorcycle . It looks something like this :



Wankel engines have also been used in motorcycles, one that I've heard of was designed for road racing :


and actually, here's a dirt bike with a Wankel : Hercules Wankel GS




It would be really interesting to try this one out and see what it's like to ride. I suppose there might have been some issues with reliability maybe? That's just a guess though, I wonder why no one tried a Wankel engine in any newer motorcycles. Maybe the same reasons why Mazda is the only manufacturer using them in the automotive industry (could anybody more knowledgeable point out these reasons ? )

[JETZcorp]

That first one's not a rotary, it's a radial.  The fact that someone put one on a motorcycle in inconceivably bad-ass.

By the way, rotaries don't use less fuel than a four-stroke; they're actually rather thirsty for their displacement.  However, given that displacement, they do have some pretty immense power-producing balls, hence Mazda getting away with 1.3L motors.  Here's what Wiki has to say.

The sealing at the Wankel apexes is less critical, as leakage is between adjacent chambers on adjacent strokes of the cycle, rather than to the crankcase. However, the less effective sealing of the Wankel is one factor reducing its efficiency, confining its success mainly to applications such as racing engines and sports vehicles where neither efficiency nor long engine life are major considerations. Comparison tests have shown that the Mazda's rotary powered RX-8 uses more fuel than heavier V-8 powered vehicles with over four times the displacement for similar performance results.

Also, the power advantage is a little controversial, because measuring displacement isn't as cut-and-dried as with a piston engine, so depending on how you measure it, they can appear way better than a four-stroke, or on-par with a four-stroke for power.

[opfermanmotors]

The reason that they quit making them is that they ran on Pancake Batter and the riders didn't like having to skip breakfast.


http://leo_keller.tripod.com/Hersteller/Hercules/opendoor/opendoor.html








"Kurt Fischer, Wankel the only rider to finish an ISDT (Hercules Wankel GS,) Gold Medal a very highly capable man."

[Out of Order]

This is a rotary kart engine. http://www.woelfle-engineering.com/

[SachsGS]

Go to Youtube and listen to a couple of the Norton rotary racebike videos.The sounds of those bikes sends a shiver up my spine.

A member of this site,Helmut Classen,has actually ridden the Hercules rotary I.S.D.T. dirtbikes and was very impressed by them.

Fichtel & Sachs also made Wankel snowmobile engines and even produced rotary chainsaws through their subsidiary Dolmar.

[2T Institute]

Wankel rotary as opposed to rotary valve engines tend to make better top end HP rather than low end, for that a reed/rotary valve engine is far better.
I know there are 13B turbo engines in sleds 350HP !

[YZ250]

By "rotary" I meant Wankel. i just thought more people would know what i'm talking about if i just used the word rotary.

[JETZcorp]

Well, as long as we're going to make this thread a clusterfuck of different applications of the word "rotary," I suppose I should take this time to once again remind everyone that I am a big believer in rotary valve induction.  I just got back from riding my own rotary-valve bike and even though it's got half the displacement, it's got the sort of crisp and immediate torque that my 250 (with reed valve) only wishes it could have.  The 250's got about four times the top-end horsepower though.

[msmola2002]

If there is anyone into radio controlled aircraft here, OS makes a small one.



http://www.osengines.com/engines/osmg1401.html

Displacement: 0.30 cu in (4.97 cc)
Practical rpm: 2,500-18,000
Output: 1.27 hp @ 17,000 rpm
Weight: 11.8 oz (335 g)

[Chris2T]

My buddy owns a Mazda RX-8, and it got me interested in the rotary engine so i spent some time lurking on an RX-8 forum. Even after decades of refinement, the RX-8 owners still say that the RX-8 shouldn't be used as a daily driver. It consumes too much gas (16-18mpg average) consumes oil (not a problem there ;-) and is high maintenance. I remember reading a couple of years ago a direct comparison of the RX-8 to a 350Z. While they produced similiar horsepower, the 350Z had nearly twice as much torque way down low.

[SachsGS]

Isn't the RX-8 motor rated at 1.3 litres vs. 3.5 litres for the Nissan? My daily driver is a Mercedes running on a 50/50 Bio-diesel mix and displays longterm reliability that makes gas powered cars seem archaic.

I think it is fair to say that the Mazda Rotary serves it's intended market well.

I remember once having seen rotary powered fire pumps on a small ship and the Maintenance Engineer said they were the best.

[JETZcorp]

So, what you're saying is, the RX-8 is like a 125 and the 350Z is like a 250F?  Except for the high-maintenance part, of course.

[SachsGS]

It should be noted that the man who invented the Wankel engine that bears his name eventually went insane.Ah,so much to look forward to in life.

[GlennC]

It should be noted that the man who invented the Wankel engine that bears his name eventually went insane.Ah,so much to look forward to in life.

I think people around him Eventually figured out he was insane