Why Don't Motorcycles Use Rotary Again?

nturtenwald · Dec 11, 2008

TheGeek said:
Rotory engines die really fast for one simple reason. Thermal expansion. The rotor grows with heat and wears the seals. When it's cooler, it leaks. Leaks cause deposits, which cause more wear. They basicly destory themselves.

That's the beautiful thing about reciprocal engines. The piston rings over lap to account for growth, and have elasticity (spring) to compensate for shrinkage. In a cold engine, without the rings installed, the piston will pretty much flop around. Heat those same parts up to operating temp and there is very little room to spare. There is just no way to keep a rotory engine sealed up when parts change size with heat.

Let's get one thing straight: Engines destroy themselves over time because of the constant frictional force associated with varied RPM use. The apex seals on the Mazda RX series generally go out at 150k, depending on the year/quality/age of seals. LISTEN: The harder you push the engine, the more quickly those seals/rings will fail. You can say the exact same thing about reciprocal engines and rotary engines The harder you push the bike, IE High RPM use, the more damage friction will do to the block, pistons (for reciprocal), or the apex seals (for rotary). How long do motorcycle engines last again? If you see a bike with 40k miles, are you running to the owner with cash in hand? The more miles on any car, the more wear and damage the engine sustains, you can say that about any car. Let's move on from the apex seals argument unless there is something NEW to add about them

You put out a point that the rings on piston engines are variable, but high RPM running will melt those rings away from the piston, and you can ask any track-only-bike owners about that. I guarantee you that the rings are the main piece that need to be replaced in a rebuild.

Also, UPDATE ON THE NEW MAZDA RX-8 ROTARY ENGINE WEIGHT: 344lbs vs. the LS1's (Aluminum block) 434lbs. Both of these weights are the engine weight, not transmission+engine+axel weight.

river rat · Dec 11, 2008

nturtenwald said:
Well they're not necessarily taking it easy through the gears, are they? That's a drag strip. Look at the inline engines on drag strips, how do they hold up? They're taken apart and inspected after each hard run. If they aren't taken apart, they're probably near-stock engines. The problem in this comparison is that there aren't any near-stock rotary bikes to compare to this because they're either fully built drag bikes or they're the bikes of yester-year that are never taken past 5k RPM

At least they make it to the finish line before having to be tore down. Just sayin...

crispone · Dec 11, 2008

I had a 13B TurboII in that "hideous" ORANGE/RED color by Mazda. I loved it, but as SOON as I began to see oil spots under it, I unloaded it at a huge discount, and was happy I did so. Blew the motor a couple months later by the mature, new owner. (He WAS a friend...)

Apex seal wear, exhaust is dirty (NOT so efficient from a fuel consumption...) and they EAT OIL like it was a consumable item for the motor...

LOOK IT UP. Even in the NEW RX-8 (I have TWO friends with them) you have to check your oil regularly, and half a quart every 1-2 thousand miles is not uncommon... and they put that damn engine cover you have to unbolt on them JUST to check the oil. DOH!

...and they just don't have a lot of torque...

Went to the Supras... and have loved all three of them since. Never go back!

LONG LIVE THE STRAIGHT SIX! (Boat motors, originally! HA!:lol)

Many "pros" for the rotary, but reliability is not one of them. I side on reliability over "smooth" and "revvy" any day.

They are also harder to get serviced by quality personnel, expensive, and sound awkward when you are on the honk...

I don't expect a big revival.

On ANOTHER note... I definitely want an RE5 one day for my collection!

-crisp

nturtenwald · Dec 11, 2008

crispone said:
I had a 13B TurboII in that "hideous" ORANGE/RED color by Mazda. I loved it, but as SOON as I began to see oil spots under it, I unloaded it at a huge discount, and was happy I did so. Blew the motor a couple months later by the mature, new owner. (He WAS a friend...)

Apex seal wear, exhaust is dirty (NOT so efficient from a fuel consumption...) and they EAT OIL like it was a consumable item for the motor...

LOOK IT UP. Even in the NEW RX-8 (I have TWO friends with them) you have to check your oil regularly, and half a quart every 1-2 thousand miles is not uncommon... and they put that damn engine cover you have to unbolt on them JUST to check the oil. DOH!

...and they just don't have a lot of torque...

Went to the Supras... and have loved all three of them since. Never go back!

LONG LIVE THE STRAIGHT SIX! (Boat motors, originally! HA!:lol)

Many "pros" for the rotary, but reliability is not one of them. I side on reliability over "smooth" and "revvy" any day.

They are also harder to get serviced by quality personnel, expensive, and sound awkward when you are on the honk...

I don't expect a big revival.

On ANOTHER note... I definitely want an RE5 one day for my collection!

-crisp

You put forward some excellent points!
1) What year was that RX-7? Now how old is the technology in that RX-7 compared to today?

2) How many miles where on that RX-7 and can you honestly say you drove the car like Honda?

3) Rotary exhaust is dirty? How about you look up the emission rating on bikes!

4) The older the engine, the more oil it burns. Run a thicker oil and you'll conserve that oil within the rings or seals. 20/50 for race RX-7s. BUT NEVER SYNTHETIC FOR ROTARY!!! I learned that from a great Mazda mechanic I still talk to for advice

5) No one has to "LOOK...UP" the fact that cars require regular maintenance. The RX-8 is no exception. Don't you check your oil on a regular basis? How about everytime you clean your chain? Vehicle inspection and checks should be regular for cars, bikes, airplanes, boats, or anything that can move! I clean my chain on a ritualized 400mile interval and do a full tire pressure check, oil check, and general inspection. If I have time, I check my oil when I get gas (after gas is pumped and bike is level).

6) I've taken off all the stupid, worthless, heat-soaking engine covers from all my cars and my friend's cars. They are useless except to make your car look pretty. They muffle the engine and heat-soak the valve cover. I've taken off the heat-shields from all my cars too, check out under the hood of my RX-7 on the pictures I posted, it's gone.

7) Rotary engines don't have a lot of torque? I agree. How much torque does your Gixxer have compared to the bike's horse power rating? Bikes don't need a lot of torque unless you're willing to pay $20k on a shiny Harley.

8) Rotary engines are "harder to service" because few have worked on them, not only that, most of the maintenance is on the sides of the rotary engine, not top. This makes the Mazda rotary servicing very difficult (and expensive) in all their vehicles, especially on the cars of yester-year. If only there was some type of small light frame that was open on the sides to put the rotary engine into that would make it easy to work on....

9) And the Supra was a boat engine, that's cool I guess. The rotary engine was originally an airplane engine. Win.

10) And there's no such thing as a reliable rotary engine at all. I've never heard of a rotary that outlasted the 100k mile mark. Never. And inline engines are so great? Especially Honda, right? I drive a Honda (when it rains, anyways) and I'm on my third engine. The chassis has 103k miles and each engine has had approximately 44k miles with regular maintenance. The rings have gone out on all my engines so far (the second engine blew it's head-gasket, block, rings, and bearings when I threw a rod; that's a sound I'll never forget). Regular maintenance on any type of engine will (usually) prolong its life, but it depends on how hard you push your car. Engine or rotary.

river rat · Dec 11, 2008

nturtenwald said:
You put forward some excellent points!
1) What year was that RX-7? Now how old is the technology in that RX-7 compared to today?

2) How many miles where on that RX-7 and can you honestly say you drove the car like Honda?

3) Rotary exhaust is dirty? How about you look up the emission rating on bikes!

4) The older the engine, the more oil it burns. Run a thicker oil and you'll conserve that oil within the rings or seals. 20/50 for race RX-7s. BUT NEVER SYNTHETIC FOR ROTARY!!! I learned that from a great Mazda mechanic I still talk to for advice

5) No one has to "LOOK...UP" the fact that cars require regular maintenance. The RX-8 is no exception. Don't you check your oil on a regular basis? How about everytime you clean your chain? Vehicle inspection and checks should be regular for cars, bikes, airplanes, boats, or anything that can move! I clean my chain on a ritualized 400mile interval and do a full tire pressure check, oil check, and general inspection. If I have time, I check my oil when I get gas (after gas is pumped and bike is level).

6) I've taken off all the stupid, worthless, heat-soaking engine covers from all my cars and my friend's cars. They are useless except to make your car look pretty. They muffle the engine and heat-soak the valve cover. I've taken off the heat-shields from all my cars too, check out under the hood of my RX-7 on the pictures I posted, it's gone.

7) Rotary engines don't have a lot of torque? I agree. How much torque does your Gixxer have compared to the bike's horse power rating? Bikes don't need a lot of torque unless you're willing to pay $20k on a shiny Harley.

8) Rotary engines are "harder to service" because few have worked on them, not only that, most of the maintenance is on the sides of the rotary engine, not top. This makes the Mazda rotary servicing very difficult (and expensive) in all their vehicles, especially on the cars of yester-year. If only there was some type of small light frame that was open on the sides to put the rotary engine into that would make it easy to work on....

9) And the Supra was a boat engine, that's cool I guess. The rotary engine was originally an airplane engine. Win.

10) And there's no such thing as a reliable rotary engine at all. I've never heard of a rotary that outlasted the 100k mile mark. Never. And inline engines are so great? Especially Honda, right? I drive a Honda Civic and I'm on my third engine. The chassis has 103k miles and each engine has had approximately 44k miles with regular maintenance. The rings have gone out on all my engines so far (the second engine blew it's head-gasket, block, rings, and bearings when I threw a rod; that's a sound I'll never forget). Regular maintenance on any type of engine will (usually) prolong its life, but it depends on how hard you push your car. Engine or rotary.

Well shit. I guess you're right then. I'm going to email the big 4 right away. I can't believe they haven't thought of this!

Sucram · Dec 11, 2008

wow, lots of misconceptions in this thread.

Take most of it with a grain of salt. Most of it is 2nd hand experience and even first hand experience can have so many vairables.

nturtenwald · Dec 11, 2008

Sucram said:
wow, lots of misconceptions in this thread.

Take most of it with a grain of salt. Most of it is 2nd hand experience and even first hand experience can have so many vairables.

[I hope you're not talking about me and my defense of rotary technology!] All of the responses to the idea of rotary-powered engines seem to be pre-programmed. It seems like the same ideas continue to be unquestioned by the majority because they have little experience with rotary altogether and all add to the fire, never knowing who started it. I see the same "they aren't reliable" comments rephrased over and over without legitimate explanations.

And great observation, Sucram, most of the stories I'm hearing are really "my brother's best friend's cousin used to drive an RX-7 and it _________" Don't get me wrong, I'm not saying none of you have vehicular experience, I'm saying most of you haven't even changed spark plugs on a rotary (Fun fact of the day: there are two different spark plugs per rotary casing, a leading plug and a trailing plug; the RX-8s may only have a 1.3L twin-rotor, but the Renesis-Wankels have 4 sparkplugs!)...

fftopic

If you are a certified Mazda mechanic and have a valid point to discuss regarding the mass-production of Wankel rotary engines, I would love to hear it. The main valid argument against rotary at the moment is that it is expensive. Why? Because it is not as common in parts or in experience. If these bikes were mass produced, we could have a revolution (pardon the pun?) in rotary technology and the prices would drop significantly. There seems to be a self-fulfilled prophecy surrounding the rotaries where no one invests in them because they're so expensive; but if people put any interest and study into them, they'd be more common and less expensive all together!

jimguyer · Dec 11, 2008

I think this is an interesting idea.
I've owned 2 RX-7s, a 1980 that I sold at 105,000 miles and a 1995 that I sold at 150,000. I had 0, absolutely 0 issues with the engines. Both were strong as new when sold, and didn't leak oil anywhere, etc etc.
I don't know what the state of the art is for high rpm behavior and lifetime. The seals are a weak spot, the apex and side seals are much harder to get right than a pretty simple circular ring.
But piston engines have weaknesses too: valves, cams, chains, large reciprocating mass (piston) held in place (hopefully) by a connecting rod. There has been a lot of research and development to make these strong, reliable. Much more so than rotaries. So I think there is opportunity here.
The result has to offer something more than cult value though or it will never be taken seriously. Same power for a lot less weight in a "literbike" ish size, or same weight more power, etc...
As has already been said with other words, small displacement with high power = low torque but high rpm operation. Our literbikes are like that...I suspect a good rotary will be too.
While I agree on the fuel mileage, I repeat still not enough research, and do we buy our literbikes for the gas mileage? I don't think so.
Good thread!

Nicko72 · Dec 11, 2008

The Norton's are comming back you may even see that bike racing against the 600's in MotoGP one day, fingers crossed. That is one amazing machine. I think they will be making twins again shortly, then one day the beast will be back.:burnout

Good to see you back Norton.

unk

GSXR1000K3BW · Dec 11, 2008

Over the years I have heard too many times that the Wankel is now reliable. It always turned out that this wasn't the case. Now I hear again: 'The Wankel is NOW reliable'.
Maybe it IS reliable now (could well be), but why take chances?
Once bitten, twice shy! My son's Nissan Maxima (3l V6) has 438,000 miles on the engine without any repairs done to it, ever. He says it uses no oil between 10,000 mile oil changes. Fuel economy and performance are as good as when new, he said.
I very much doubt a Wankel lasts that long.
You said: "I drive a Honda (when it rains, anyways) and I'm on my third engine. The chassis has 103k miles and each engine has had approximately 44k miles with regular maintenance. The rings have gone out on all my engines so far (the second engine blew it's head-gasket, block, rings, and bearings when I threw a rod."
How do you drive? Is the needle of your revcounter always in the red zone?
High torque is very important to me (Wankels have little) that's why I would never buy one.
It is very hard to recover from a bad reputation. A lot of people have lost a lot of money.
The famous NSU brand was destroyed by the Wankel. Heard of the NSU Ro 80?

crispone · Dec 11, 2008

nturtenwald said:
9) And the Supra was a boat engine, that's cool I guess. The rotary engine was originally an airplane engine. Win.

WIN? Not sure I follow... just because the rotary was once an airplane engine... especially when IT is going the way of the DODO bird, and the STRAIGHT SIX is STILL an engine that continues to be utilized in a variety of vehicle configurations with great success, performance, reliability, efficiency, and economy within the industry... NOT ONLY limited to the automotive.

nturtenwald said:
If you are a certified Mazda mechanic and have a valid point to discuss regarding the mass-production of Wankel rotary engines, I would love to hear it. The main valid argument against rotary at the moment is that it is expensive. Why? Because it is not as common in parts or in experience. If these bikes were mass produced, we could have a revolution (pardon the pun?) in rotary technology and the prices would drop significantly. There seems to be a self-fulfilled prophecy surrounding the rotaries where no one invests in them because they're so expensive; but if people put any interest and study into them, they'd be more common and less expensive all together!

I'm not sure I understand WHAT IS YOUR AGENDA? You challenge the rest of us "peanut gallery" with statements such as "IF you are a certified Mazda mechanic AND have a VALID point to discuss..."

WTF? Are YOU a WANKEL EXPERT with CERTIFIED STATUS to PROMOTE them? Did YOU just buy STOCK in a company holding RIGHTS to the rotary? Are YOU about to cash in on royalties IF they become widely accepted in society and industry?

I have nothing "against" rotary engines in particular, but I not sure I have seen a GOOD, STRONG, FACTUALLY SUPPORTED argument that should PERSUADE any of us to suddenly become BIG FANS and PROPONENTS of ROTARY REVIVAL either. Heck, why not more BOXER configurations? Why not stump for HYBRIDS? Electric cars? Hydrogen cars? MULTI-FUEL burners?

You, my friend, have a CLEAR AGENDA to promote your rotary fantasies at the rest of us. That's fine... but biting rebuttal directed at ALL NON-AGREEABLE responses that are PART of this thread discussion... accompanied by critical dismissal EVEN of our (MY) personal experiences will likely find little favor in your court.

That having been said... I'm subscribed and will CONTINUE to read and reflect on the "statements" (claims?) made by yourself and others in the interest of eventually (or possibly) coming across something edifying or otherwise anecdotal from this dialogue... since honestly, I don't care either way... as ANY configuration/design/development relative engine technology (current/past/or future) is interesting to follow...

Now then... please continue oh sage of Dorito-driven combustion...:chucks

PS: I'm skeptical of ANY statements made by someone who goes through THREE (3) HONDA ENGINES in just 100k miles... REGARDLESS of what kind of snake-oil they were trying to sell me...

-crisp

Stocky · Dec 11, 2008

You guys want to have a look at the XR50 Kart engine.

It's 250cc (well kind of)

Less than 20Kg

And makes 50 - 60 HP depending on tune.

The torque is off the hook. The thing pulls like a freight train.

You'd easy get a "twin rotor" version into a bike frame with a gearbox at about half the size and weight of an inline 4.

Even keeping the tune simple to keep the reliability it'd make 120HP but it'd make way more torque than an inline 4 and be much lighter.

In the end though, it wouldn't do 100,000 miles

It wouldn't pass emmisions laws (has oil in the fuel)

But it'd be aweful fun to ride LOL

dhoard · Dec 11, 2008

Stocky said:
You guys want to have a look at the XR50 Kart engine. ...

That definitely looks interesting ... bet that would be a blast on a kart or a fifty.

http://www.cometkartsales.com/store/engine/aixro.htm - $5800

-Doug

Tyg · Dec 11, 2008

Well hell... I'd love to get involved, but my knowledge surrounding engines is damn near zero.

I had no idea rotary engines were even developed for motorcycles. Learned something new today and I'm happy

TheGeek · Dec 11, 2008

nturtenwald said:
Let's get one thing straight: Engines destroy themselves over time because of the constant frictional force associated with varied RPM use. The apex seals on the Mazda RX series generally go out at 150k, depending on the year/quality/age of seals. LISTEN: The harder you push the engine, the more quickly those seals/rings will fail. You can say the exact same thing about reciprocal engines and rotary engines The harder you push the bike, IE High RPM use, the more damage friction will do to the block, pistons (for reciprocal), or the apex seals (for rotary). How long do motorcycle engines last again? If you see a bike with 40k miles, are you running to the owner with cash in hand? The more miles on any car, the more wear and damage the engine sustains, you can say that about any car. Let's move on from the apex seals argument unless there is something NEW to add about them

You put out a point that the rings on piston engines are variable, but high RPM running will melt those rings away from the piston, and you can ask any track-only-bike owners about that. I guarantee you that the rings are the main piece that need to be replaced in a rebuild.

Also, UPDATE ON THE NEW MAZDA RX-8 ROTARY ENGINE WEIGHT: 344lbs vs. the LS1's (Aluminum block) 434lbs. Both of these weights are the engine weight, not transmission+engine+axel weight.

Just talking about the physics of why the seals wear and how the design does not account for normal wear like a piston engine. Sure, anything that makes contact is going to wear out. Piston rings are designed to somewhat compensate for that as well as thermal expansion. Apex and side seals have no compensation for either. You're asking why we don't see more rotory engines. They're simpler, lighter, and easier to manufacture. Why don't we see them in more cars? Because they are more likely to fail than a piston engine. I don't care how good the technology has gotten, the physics of it haven't changed.

Why Don't Motorcycles Use Rotary Again?

nturtenwald

river rat

crispone

nturtenwald

river rat

Sucram

nturtenwald

jimguyer

Nicko72

GSXR1000K3BW

crispone

Stocky

dhoard

Tyg

TheGeek

Top Contributors this Month

Recommended Communities