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explain rotary motors to me
I dont know much about rotary engines. I have a friend who cant get his engine running. He bought a used motor, rebuilt it, and cant get it to run and asked for my help. I understand how the engine cycles work but i think he is having a timing issue maybe. He had 60 PSI of compression and then took it back apart and went through it again, and now has 80psi. ( i know right?) But anyway, he says the rotors can only go onto the eccentric shaft one way. ( then why is his compression different now?) I have looked at a few websites and cant figure what turns what in a rotary engine.
TurboRX7.com > Rotary Engine Block pictures shows some good pics, but not all i need to see. So i guess my question is, does this motor need to be 'timed' in any way? Do the rotors simply fit over the shaft in any position? What turns them? etc.. lol.. |
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Diss Member
Join Date: Jul 2002
Location: SC - (Aiken in the 'other' SC)
Posts: 5,022
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Ahhhh, flopping lobe motors...
Yes the rotors will only go in in the correct position. If it assembled (with all the seals) then that part is ok. This link has a decent animation part way down to help you visualize the way things go together: http://www.rotaryaviation.com/ A rotary is a 2 stroke motor. It has no valves so that can't effect compression but the seals on the rotors don't seal real well when initially assembled. I can easily believe that you could get that kind of compression increase just by managing to get a better seal during assembly To get an idea of how the seals "need some help" in a rotary: We would generally see the dyno numbers on a 13B increase during break in with it reaching its peak after an average of 13 hours of run time. Basically you are up against the basics of combustion: Compression, fuel, and fire. It seems that either the issue is spark/timing or fuel delivery. That is what to chase down.
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- "Speed kills! How fast do you want to go?" - anon. - "If More is better then Too Much is just right!!!" - Mad Mac Durgeloh -- Wayne - 87 Carrera coupe -> The pooch. |
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Formerly known as Syzygy
Join Date: Mar 2008
Location: Calgary, AB
Posts: 4,420
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All I know is the piston engine goes boing, boing, boing, but the Mazda goes mmmmm...
![]() Mazda RX-3 Commercial - YouTube
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Kevin 1987 ROW coupe, Marine blue, with a couple extra goodies. The cars we love the best are the ones with human traits, warts and all. |
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too funny, as this is an aviation engine! But i still dont see how the rotor connects to the eccentric shaft..
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Racer
Join Date: Oct 2010
Location: Franklin, TN
Posts: 5,887
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Max Sluiter
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Gear teeth. Sort of like a planetary gearbox.
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance |
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Max Sluiter
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Really? I had never heard of a 4 stroke rotary. The RX-8 is a two stroke from all I have heard, so why go from 4 to 2 with the ever tightening emissions restrictions. How does that differ from all the other 2 stroke ones?
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Everything ive read/seen videos on so far, says they are all 4 strokes.. They have intake, compression, power and exhaust. And the rotor attaches to a fixed gear on an intermediate plate, whereas is just slips over the eccentric shaft. I was wondering if there was a way to put the rotor on the e-shaft 'out of time' so to speak. Like slipping the rotor on where one of the apex is pointing at 12oclock as compared to 2 oclock. Does that make sense?
or that it doesnt matter how it goes on initially, as it will time itself as the e-shaft spins?? |
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Navin Johnson
Join Date: Mar 2002
Location: Wantagh, NY
Posts: 8,812
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I have heard they are two stokes.... so who knows what is correct..
I do know they need an ignition set-up with "split-timing" and if you don't get the timing split correct the engine will not run, or will run and self destruct in short order.. We have a RX-7 in the shop that the owner abandoned, that we saw over 500hp on a two rotor turbocharged rotary.... The owner wanted Haltech so we worked with Oz snd got the timing split corrected and engine running very strong.... then the owner disappeared.....
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Registered
Join Date: Dec 2008
Location: San Antonio, Texas
Posts: 3,591
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If you stood next to one in the pits you would know they are 2 strokes.
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1973 911S (since new) RS MFI specs 1991 C2 Turbo |
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Wankel (rotary) engines are indeed "4-stroke" combustion engines. They are commonly misunderstood as "2-strokes" as they appear to compress/ignite without a valve train and are often confused with 2-stroke reciprocating motors.
Wikipedia does a rather good job of describing how these work: Wankel engine - Wikipedia, the free encyclopedia |
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Navin Johnson
Join Date: Mar 2002
Location: Wantagh, NY
Posts: 8,812
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Quote:
At an IMSA race in the early eighties... Mazda had a few cars at Lime Rock... they were quite possibly the loudest racecars I have ever heard..
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Don't feed the trolls. Don't quote the trolls ![]() http://www.southshoreperformanceny.com '69 911 GT-5 '75 914 GT-3 and others |
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sorry.. Scott is correct they are 4 stroke motors, as a general rule I don't think they win on efficiency, the cr is somewhat limited by the geometry but this was some years ago, some of the issues probably have been resolved. I like them myself, the power per pound is very good. Years ago a guy had one in a Super 7 and all but dominated the So. Cal. AX circuit. I think his name was Jim. Somewhere the pros/cons are likely listed, I think it would be a good motor for a e.g. 356. There are a few companies that specialize in hot rodding them.
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Navin Johnson
Join Date: Mar 2002
Location: Wantagh, NY
Posts: 8,812
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OK curious George got me... I Googled Wankel and the Wiki explanation is that it is a four cycle engine...
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Max Sluiter
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Well, all engines must have a way to have intake, compression, power, and exhaust.
A Wankel (read the Wiki before the link was posted) has one power stroke per combustion chamber per revolution, twice as many as a 4 stroke piston engine, so that sounds decidedly 2 stroke to me. I think the differences in design between the engines make comparing them hard, but with a rotary being worth the power of a piston engine twice as big, together with the lack of valves I would consider it a 2 stroke. Especially with their appetite for oil and fuel.
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance |
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Navin Johnson
Join Date: Mar 2002
Location: Wantagh, NY
Posts: 8,812
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In any event, whether it is a two, four or miller cycle engine...
The rotary requires special ignition timing... Is the engine in question being run with the stock ECU? or aftermarket?
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I found this to be the best mod to keep my RX7 running
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Diss Member
Join Date: Jul 2002
Location: SC - (Aiken in the 'other' SC)
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Quote:
If you look at the wikipedia page and its diagrams that show the "4 strokes" you will notice that the rotor completes all "4 strokes" on a single rotation. The crank rotates 3 times for every rotation of the rotor but that is a pretty flimsy excuse for a "stroke". ![]() The wikipedia article does not say that the rotary is a 4 stroke. To quote the wikipedia page: "In the Wankel engine, the four strokes of a typical Otto cycle occur in the space between a three-sided symmetric rotor and the inside of a housing." This statement is factually incorrect. The "Otto Cycle" is a very specific term that refers to reciprocating piston engines. The correct phrasing of the wikipedia quote should be: In the Wankel engine, the functional equivalent of the four strokes of a typical Otto cycle occur in the space between a three-sided symmetric rotor and the inside of a housing. Everything about a rotary will tell you it is 2 stroke. No valves and all intake and exhaust timing is done by modifying the ports. Every time the combustion chamber comes by it is ignited. Every time a face of the rotor comes by the intake charge comes in. Every time the rotor face passes the exhaust port the burnt charge is expelled.. You have to run a straight through muffler on it. (reverse flow mufflers will balloon or explode!) Loud enough that your ears will ring even though you have ear plugs in and a 3-1/2 foot glass pack on it. Their emissions stink unless you cook them in a converter.
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- "Speed kills! How fast do you want to go?" - anon. - "If More is better then Too Much is just right!!!" - Mad Mac Durgeloh -- Wayne - 87 Carrera coupe -> The pooch. |
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Racer
Join Date: Oct 2010
Location: Franklin, TN
Posts: 5,887
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Quicksilver,
No, you are incorrect. The RX-7 Wankel is a four cycle engine. No doubt about it. Just because it does all four cycles in one revolution does not make it a two cycle engine. Scott |
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