Why hasn't someone put a Rotary (Wankel) engine in a motorcycle yet?
04-13-2009, 09:39 AM
#1
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Squid
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Why hasn't someone put a Rotary (Wankel) engine in a motorcycle yet?
Just curious:
All that talk in the other thread about I4's vs V4's - just wondering why someone hasn't put rotary engines in bikes yet? A simple google search shows that one company has - http://www.rotabike.com/ , but again, I've never heard of one of these anywhere.
Just thinking back to my car racing days, and how the properties of Mazda rotary engines allowed for CRAZY high RPM's in a car (I think 16k, right?) and that turbochargers on said cars made them insane. Yes, you had to rebuild the engine every 50k or so, but I'd think that would still be pretty sweet in a sport bike. Or any motorcycle for that matter. Just smooooooooooth power.
What do you guys think? Why is a rotary engine seemingly such a bad design in a motorcycle?
All that talk in the other thread about I4's vs V4's - just wondering why someone hasn't put rotary engines in bikes yet? A simple google search shows that one company has - http://www.rotabike.com/ , but again, I've never heard of one of these anywhere.
Just thinking back to my car racing days, and how the properties of Mazda rotary engines allowed for CRAZY high RPM's in a car (I think 16k, right?) and that turbochargers on said cars made them insane. Yes, you had to rebuild the engine every 50k or so, but I'd think that would still be pretty sweet in a sport bike. Or any motorcycle for that matter. Just smooooooooooth power.
What do you guys think? Why is a rotary engine seemingly such a bad design in a motorcycle?
04-13-2009, 11:25 AM
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04-13-2009, 01:25 PM
#10
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My guess is that it would make for funky handling. Too much centrifugal force when placed one direction and too complicated to mount transmission when placed the other way.
AND, is 160+ from a bone stock I-4 no good?
Cheers.
AND, is 160+ from a bone stock I-4 no good?
Cheers.
04-13-2009, 02:37 PM
#12
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More specifically, http://www.realclassic.co.uk/norton06120100.html
That thing has potential. It'll be REALLY noisy.
That thing has potential. It'll be REALLY noisy.
04-13-2009, 02:49 PM
#13
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In 2006, Yamaha release the R6 With a claimed 17,500 RPM redline, but actual dyno testing proved that the rev limiter kicked in at 16,000. Why would the Japanese Motorcycle manufacturers be inclined to produce a rotary engine when we already have high rev capable inline-4's in current production?
04-13-2009, 03:00 PM
#14
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Simplicity and lighter weight. The rotary in that 2007 Norton is much smaller than a piston engine with no valve train and far fewer moving parts. Rotarys have always been a good idea, just under explored.
04-14-2009, 06:38 AM
#16
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After reading up on some of those threads I can see why they didn't really persue Wankel type engines. SOmetimes, I just wonder what the motorcycle world would have been like had they actually put all that development into a rotary engine instead of regular pistons. Thanks for the links!
04-14-2009, 07:23 AM
#17
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If these motorcycle rotaries are to be anything similar to the RX-7's, 8's etc. it would be a waste of your time and money. And with the constant maintenance and upkeep it's sure to keep you in the poor house. But hey, What would Obama do?
04-14-2009, 07:38 AM
#18
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^not ture^(in my experience). I had an RX7 that was pretty tricked. Ran like a top for 100,000 miles, and I ran it hard a lot. There's really nothing in them to go wrong since there's so few parts and the two largest/heaviest parts move at 1/3 the speed of the output shaft. They used to lack bottom end torque, I don't know what's been done over the years to overcome that.
Circut Burner, there's a few guys out there that have cronicled their aero conversions to rotarys at length on the web. Pretty interesting stuff.
Circut Burner, there's a few guys out there that have cronicled their aero conversions to rotarys at length on the web. Pretty interesting stuff.
04-14-2009, 09:47 PM
#19
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They make good light helicopter engines.
seen a mini-500 with an RX7 engine. slightly overpowered in my opinion.
Would work great on a Rotorway or similar.
Had the whizzy sound without the 30,000 dollar turbine upgrade.
seen a mini-500 with an RX7 engine. slightly overpowered in my opinion.
Would work great on a Rotorway or similar.
Had the whizzy sound without the 30,000 dollar turbine upgrade.
04-14-2009, 10:09 PM
#20
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Rotary's got a bad rap in the early 70's because mechanics didn't know how to set the timing. They had dual ignition (they still do, 2 plugs per cyl) with 2 separate distributors with breaker points. Like all point type ignition it required a tune-up every 12k miles.
One distributor was for the leading spark plugs (timing set at 10 deg BTDC), the other for the trailing plugs (timing set at 3 deg BTDC). Mechanics who didn't set the timing correctly would end up burning the Apex Seals (rotary equivalent of piston rings), resulting in high oil consumption.
The problem was solved after the first few years when Mazda combined the dual ignition into one distributor, and of course now they have Direct Ignition (DIS). They also changed the material used for the Apex Seals. I've seen RX's with over 250,000 miles.
One of my former students went to work for Mazda in Irvine, CA in the 90's. He rebuilt warranty engines. He said it took about 45 minutes to rebuild one.
One distributor was for the leading spark plugs (timing set at 10 deg BTDC), the other for the trailing plugs (timing set at 3 deg BTDC). Mechanics who didn't set the timing correctly would end up burning the Apex Seals (rotary equivalent of piston rings), resulting in high oil consumption.
The problem was solved after the first few years when Mazda combined the dual ignition into one distributor, and of course now they have Direct Ignition (DIS). They also changed the material used for the Apex Seals. I've seen RX's with over 250,000 miles.
One of my former students went to work for Mazda in Irvine, CA in the 90's. He rebuilt warranty engines. He said it took about 45 minutes to rebuild one.
Last edited by VTRsurfer; 04-14-2009 at 10:11 PM.
04-14-2009, 11:57 PM
#21
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The one major rotary drawback always, theyre fuel hogs.
They will always be less efficient than piston engines.
Even the model airplane wankel from O.S. , 5 minutes fly time on the same
tank we flew for 10 minutes with piston.
They will always be less efficient than piston engines.
Even the model airplane wankel from O.S. , 5 minutes fly time on the same
tank we flew for 10 minutes with piston.
04-15-2009, 07:17 AM
#22
Remember stock is BAD!
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Rotarys are great if you are looking for power to weight ratio, or at least 10 years ago this was true. The problem that they had with them before was that the seals would not last long, consequently they needed to be rebuilt after 100k miles. There are also less moving parts in a rotary, leading to a more reliable engine, in theory anyway.
04-15-2009, 07:53 AM
#23
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Direct induction two-strokes 
Have a close look at the Evinrude E-TEC engines (the tech has also migrated to snowmobiles, a 600 cc twin putting out 120 hp while using less fuel than a four-stroke, all the while burning VERY LITTLE oil and producing no smoke or smell).
Have a close look at the Evinrude E-TEC engines (the tech has also migrated to snowmobiles, a 600 cc twin putting out 120 hp while using less fuel than a four-stroke, all the while burning VERY LITTLE oil and producing no smoke or smell).
04-19-2009, 08:35 AM
#25
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The Wankel is over-rated for all applications other than pure racing applications. Its an interesting design from the standpoint that it gets close to the efficiency of a 4-stroke with the power of a two stroke because there's no non-power stroke in a Wankel.
Also, because there is no reciprocating movements in the engine, it can spin at extremely high rpm (I think the Mazda LeMans car ran with a redline around 22k, forced LeMans to come up with special displacement rule for rotary engines after Mazda literally left the competition in the dust). The problem with redlining at this rpm, is that the side and apex seals wear at a crazy rate at these rpm. That's not an issue in a race car as the engine will be torn down and rebuilt after every race, but it sure as hell is an issue in a production car that needs to run at least 150k without major engine work. Hence the RX7's redline of only 7K.
I have an '88 RX7 convertible and its a blast to drive, but not because of the engine. Mazda's real achivement with that car was the frame, suspention, and layout. The mid-engine mounting gives the car a 50/50 weight distribution and the 5-way flex rear hubs give the car passive four wheel steering. The thing just sticks to corners and if it does break side traction, it doesn't slide, it just predictably moves out until I reduce the side force by slowing or straightening the wheel. I have yet to scare myself by taking a corning too fast, the thing just takes the speed/force and keeps going where I point it.
If I ever decide to make a project out of the car the first thing I would do is dump the 13b rotary and drop in a good old piston engine. There's some great mechanics out there that have taken domestic V8's, replaced a bunch of parts with light weight alloys, and when everything is installed and running, the car is actually lighter than stock. HP goes from 130 (or 210 with the 13b turbo) to 300+ and the car is actually lighter. Weight distribution is essentially unchanged as well. I think I've heard of people doing it for under $4K...
Also, because there is no reciprocating movements in the engine, it can spin at extremely high rpm (I think the Mazda LeMans car ran with a redline around 22k, forced LeMans to come up with special displacement rule for rotary engines after Mazda literally left the competition in the dust). The problem with redlining at this rpm, is that the side and apex seals wear at a crazy rate at these rpm. That's not an issue in a race car as the engine will be torn down and rebuilt after every race, but it sure as hell is an issue in a production car that needs to run at least 150k without major engine work. Hence the RX7's redline of only 7K.
I have an '88 RX7 convertible and its a blast to drive, but not because of the engine. Mazda's real achivement with that car was the frame, suspention, and layout. The mid-engine mounting gives the car a 50/50 weight distribution and the 5-way flex rear hubs give the car passive four wheel steering. The thing just sticks to corners and if it does break side traction, it doesn't slide, it just predictably moves out until I reduce the side force by slowing or straightening the wheel. I have yet to scare myself by taking a corning too fast, the thing just takes the speed/force and keeps going where I point it.
If I ever decide to make a project out of the car the first thing I would do is dump the 13b rotary and drop in a good old piston engine. There's some great mechanics out there that have taken domestic V8's, replaced a bunch of parts with light weight alloys, and when everything is installed and running, the car is actually lighter than stock. HP goes from 130 (or 210 with the 13b turbo) to 300+ and the car is actually lighter. Weight distribution is essentially unchanged as well. I think I've heard of people doing it for under $4K...
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