i probably should have put this in the Off Topic section but I think it has to do with dirt bikes...   somewhat...

I was just thinking about rotary engines and how they can produce very smooth and reliable power, and more power than piston engines.  Why not put them in a dirt bike?  

they have less moving parts, smoother power transmission, and are able to reach much higher RPM's becuase they only move in one direction as opposed to a piston that violently moves up and down.

I think one of the manufacturers should try and design one, that would be cool to see.

Anyone think it would be a good idea?

kawasaki uzed to use them for sure in there dirt bikes because i use to own one  . thinking it was a 1972 250 enduro idid some fiddeling with the motor and at the time could wheelie in all 5 gears 1/4 to 1/2 mile the the straight away ran out. this was back when the motessa. bultaco, rickman,cz, pentons,huskys were the bikes at the time. yamaha had the dt, and suzuki was a tm not a rm yet.

I believe a problem is that the tip of  the "piston" wears out due to a smallish contact area with the wall of the cylinder.

Rannoch said:

Be the apex seal, but piston rings also wear out. A rotary with 2 rotors is like a 6 cylinder 2 stroke. Gobs of power!

The early seventies Kawasaki's were Rotary Valve engines, not Rotary engines.  They were two stroke engines with the carb mounted on the side (right side, normally) of the crankcase, under an aluminum cover.  The advantage of a rotary valve in a two-stroke without a reed is that it allows the intake port to be opened and closed asymmetrically, or at two different points in the rotation of the crank.  Using the piston skirt to controll the port opening, as was otherwise the common practice, required the port to close at he same number of degrees ATDC that it was opened BTDC.  The rotary valve could open the port earlier, and then close it before a backflow began at low speeds, giving it better low speed performance then a piston-port engine with  similar timing.

Rotary engines have poorish low speed performance, but rev very well.  Their power advantage is similar to that of a two-stroke over a four-stroke, in which the two-stroke fires twice as frequently.  The Rotary produces about two powercycles per crank revolution (3 per rotor cycle, geared down internally).  My biggest issue with the ones I worked on in cars is that they were nearly impossible to troubleshoot, since everything that happened to them seemed to produce the same symptom; it wouldn't run.

thers a reason there not popular. mazdas the only one and only use it in one car . they seem like more trouble and dont make that much of a difference

my friends got an rx8 and it has alot of high end power it is slow off the starts.

You would think the centrifugal force of the rotor would make the bike hard to handle in the turns.

The biggest problem with the Wankel (rotary) is it's lack of development.  Given more $, it could produce very impressive results.

Right now they use a bit too much fuel, and create very significant amounts of heat.

However, they'll run on super low octane fuel, are a perfect match for hydrogen, and are physically small.

Great idea, and Suzuki made a real rotary bike (the RE5 I think) several years ago.

toyota_mdt_tech said:

What he said. That was the main problem with boosting the older RX-7's. I think they beefed it up on the RX-8. They also aren't very good on fuel economy and take massive RPM to build up to peak whp. But it's fun to drive a car with them and listen to one un-corked. They sound crazy.

Saw this neat new engine design.  It is a rotary motor that uses piston compresion.  Heres the site [URL=http://www.quasiturbine.com/].  Scroll down the page and it will show you how it works.  It makes sense to me and seems very efficient and with promising potential.

I think that Norton made a rotary bike.  They can be made to make power.  In the early 70's before GM sold the rights to Mazda they made a 4-rotor 450hp Vette.  But it got terrable gas milage (remember what was going on in the early 70's with gas)  Had Very high exhaust temps and was a very dirty engine.  They do not know the word torque and you have to keep the things way up in the rpm range for them to make power.  Good design only 3 real moving parts.  If you have ever been around a racing rotary you will know what it is the second it is started up.

they have been used in some snowmobiles and suzuki even put one in a streetbike, but i dont think there has ever been one in a dirt bike.  might be kinda cool, but as mentioned already, they tend to wear out pretty fast.

it would be cool, but rotary's arn't realiable, at least in my experience with them in
RX-7's they don't like to be run lean, infact my friend blew his engine because of detenation due to cheap gas, still 91, but some no name station. But this is a turboed application, not sure if they are a bit more forgiving without boost.

RMZrider397 said:

I doubt that. Rotary engines dont need high octane fuel.
*EDIT* I just saw the part about it being a turbo. That may have had an effect.

you could have a tiny little engine in a bike frame and it would giver shit. if somebody makes a good design, it may change the way we think about dirtbikes...

RMZrider397 said:

Just because the RX7's rotary was not reliable don't mean that a rotary engine can not be made reliable. A Vega's engine was not reliable but that's not to say that all piston engines are unreliable.

I've had 5 RX-7's, all very reliable.  The only issues I ever had was with exhaust- on a 1979 model with the thermal reactor, it melted a hole in it.  Welding a bit of steel over the hole resulted in another hole once it melted the steel.  The thermal reactor was used as a way to get around the catalytic converter, and was located as a exhaust manifold.  The other issue was a melted cat.  Once it was hollowed out the car was much quicker, and much louder.  Pretty good record, especially considering how abusive I used to be with vehicles.

Non-turbo rotaries need an octane rating just above kerosene, turbo's are a whole different deal.  They usually die not because of detonation, but because running them lean melts everything, though detonation is still not appreciated by them.

cherokee said:

Norton did indeed use rotary motors in their attempted return in the late 80's and early 90's.  They had awesome racebikes, especially at the Isle of Mann.  But the streetbikes weren't very well developed.  In the early 70's Suzuki came out with the RE5 street bike.  It wasn't any more powerful than any of the piston powered bikes it was marketed against.  It was heavier, and ran much hotter.  They only produced it like one or 2 years.  Hercules(also know as DKW) had a couple years trying a Wankel motored bike in the mid 70's, but it was air cooled.  My father actually road raced one against 2 stroke 250s between 1979 and 1983.  Only recorded one DNF, and that was an endurance race in the rain where the motor just drowned.  It was a pretty good handling bike, actually, but not enough power for long straight aways.

Even though the rotary motor should have better power to weight ratio than traditional piston motors your still dealing with a dirty, LOUD, and hot running motor.  But they do sound sweet at full song.

It's rumored that Mazda holds all the patients on rotary motors now.  So if you want to manufacturer a vehicle with one, you have to pay them to do it.

Suzuki made the most sucessful Rotary motorcycle ever....the RE-5, made from 1974-1976.  Here is a link if interested:
http://www.suzukicyc...E5-Rotary.shtml

What was interesting, if you look closely at one of the pictures you will see air scoops in the exhaust downpipes, under the radiator.  Due to the extremely high exhaust gas temperatures (1500F) in a rotary engine, the exhaust was double walled, with the air scoops forcing air down between the two ....so the rider would not burn his legs off if you got to close to the exhaust.

A very unique bike to say the least.