Mazda rotary engine and 2 cycle in the gas tank.

[digitalSniperX1]

Ok, I'm far from an expert and there are many opinions on this topic but I'm wondering if their are any good opinons/experience on this site....

Mazda rotaries, specifically the Renesis which was unveiled with the RX8 in 2004, are known for their high failure rates.

The failures are thought to result from 2 competing issues.
(1) Excess carbon generation, due to the motor oil injection into the combustion chamber. This carbon causes at least 2 apex seal failure conditions and perhaps one valve failure condition.
(2) Lack of lubrication in the combustion chamber due to lack of oil volume injected.

I'm sure and (1) and (2) above are over simplified. However, if interested, please read on.

Potential solutions to this problem are

(1) add 2cycle oil to the fuel.
(2) effectively bypass using engine motor oil by installing external oil tank and supplying it with 2cycle oil.

The 2cycle oil theory comes from the fact it's made to be burned.

My questions are

(1) any reason(s) to not agree with these outright?
(2) what negative effects of the 2cycle oil injection should be taken into consideration? For example, catalytic converter damage comes to mind.
(3) what considerations should be made in selecting the 2cycle oil.

Any input would be greatly appreciated.

Thanks

 

[simple_gifts]

Why not use Pennzoil Platinum, probably the best oil out there for the money.... 8)

 

[digitalSniperX1]

I don't think it's recommended in 2cycle applications. Give it a try in your echo weed wacker and let us know. Or is that 2003 echo a toyota? nevermind, not much difference

 

[kd5byb]

Good afternoon all,

Let me start my post by saying that I know very little about the Renesis motor, other than I used to have a coworker that had one in his RX8. Seemed to purr like a kitten and go like the wind.

It seems to me that regular engine oil is formulated NOT to burn, and that injecting motor oil into the fuel before it gets burned in the Renesis motor just isn't a great idea.

Example: A friend of mine has a Mercedes diesel converted to run on waste veggie oil. One day after the local county recycling refused to recycle my used motor oil, I asked him if he wanted to run my waste motor oil through his diesel. I figured it would be GREAT fuel as it was mostly waste M1 oil, but he noted that this wouldn't work, as motor oil is formulated for a high flash point that makes ignition of it in a diesel engine difficult.

This seems reasonable - we here at BITOG get cranked up when the flash point of motor oils are lower than we'd like, either in a UOA or VOA.

I can see why Mazda would do it - it's a lot easier to feed engine oil in than ensuring people keep a separate 2-cycle oil tank full. It's hard enough getting most people to check their engine oil and keep it full, nevermind a second tank for injection 2-cycle oil.

All that said, it seems like 2-cycle oil in the gas that's designed to burn would be better than motor oil which is NOT designed to burn...

later,
b

 

[digitalSniperX1]

Good reasoning on all of it. Esp the fact Mazda opted for using engine oil. Many can't even be bothered checking that, let alone having to fill up a separate reservoir.

 

[simple_gifts]

Quote:

Give it a try in your echo weed wacker and let us know. Or is that 2003 echo a toyota? nevermind, not much difference

Correct, they consume about the same amount of gasoline in an afternoon of use.

 

[digitalSniperX1]

And produce about the same amount of HP. The weed wacker makes a nicer sound though.

 

[gtx510]

Do you guys think a top end lube would burn cleaner and would it lube the seals enough?
http://www.liquidhorsepower.com/top-lube.php

 

[SkiTechPro]

Back in the early eighties a good friend of mine had a rotary wagon that was set up by Mike Lowe Performance in Sarasota, Florida..One of the first things that was done was to convert to pre-mix using motorcycle 2 cycle oil (Golden Spectro) in order to extend the life of the apex seals...Here is a link to his shop http://www.loweperformance.com/

 

[digitalSniperX1]

Good info. Thanks. I think I'm going to do it also. An OMP (oil metering pump) adapter is a available from Richard Sohn...a great 100 dollar modification, perhaps the best. The OMP adapter was designed for use in experimental aircraft that run mazda rotary engines. I'm about to order one.

 

[digitalSniperX1]

Not sure about that product. I'm using FP+ and Amsoil's Saber pro on advice of some pretty knowledgeable people.

I've noticed less carbon in the exhaust pipes running it along with Amsoil's XL 5W-20.

 

[mjoekingz28]

There just HAS to be some negatives for using premix, but the one I can think of is that it will lean your A/F and lower the octane of the fuel.


I tried adding 2 cycle oil after a few months of owning the car. I would mix 400:1 or so for a tank then I wouldn't premix the next tank of gas. In my mind, the engine seemed to purr smoother + all them club guys says its "additional protection" so I just kept running it.

I also tried 'air-cooled' 2 cycle oil in one tank and it just felt nasty. So, as long as it is TCW-3 you should be fine.

 

[digitalSniperX1]

I'd say the negatives probably start with fuel pump and fuel injectors. After that, hmm, not sure.

Perhaps off the topic, I've definately noticed less soot in the exhaust using 2cycle premix vs. Lucas UCL. Almost none in fact. With the Lucas in there, more.

I can't be sure that driving habits and fresh Amsoil XL 5w-20 didn't help that out too, although the oil that it was exchanged for had only 2000 miles on it (Quaker State, what the dealer uses and never again).


So for now, I'm sticking with the 2 cycle. My experience has been the same as yours, purrs all the way to 9000 rpm with that stuff in the tank.

 

[wapacz]

another question would be which one has less effect on the cat.

 

[gtx510]

How would LC20 burn? Think it would clean the housings/"chamber"?
How would it lubricate compared to engine oil?
It's got less additives than oil so it might poison the cat less?

 

[digitalSniperX1]

Originally Posted By: wapacz
another question would be which one has less effect on the cat.


No doubt, forgot about that one. Of course the guys who'd know from experience might answer "what cat"?, lol.

LC20 in the tank...interesting...I wonder how it mixes with gasoline laced with FP+.

 

[bdcardinal]

when you said valve failure, what valve were you talking about? the renesis has no valve train, at least ive never been able to find one on my parts lookup..

 

[digitalSniperX1]

Originally Posted By: bdcardinal
when you said valve failure, what valve were you talking about? the renesis has no valve train, at least ive never been able to find one on my parts lookup..


I think I meant port, and specifically the exhaust port. I have read some refer to the port as a valve. I'm not sure why because I'd associate valve with a moving part. Not sure if there is a moving part in there or not.

I believe the failure is that they become clogged with accumulated carbon deposits.

As you said, there of course is no camshaft/valve train as there is in a 4 cycle combustion engine.

 

[Audi Junkie]

An Audi design, originally, it was...


http://en.wikipedia.org/wiki/Wankel_engine


"Compared to four stroke piston engines, the time available for fuel to be port injected into a Wankel engine is significantly shorter, due to the way the three chambers rotate. The fuel-air mixture cannot be pre-stored as there is no intake valve.

The surface/volume-ratio problem is so complex that one cannot make a direct comparison between a reciprocating piston engine and a Wankel engine in relation to the surface/volume-ratio. The flow velocity and the heat losses behave quite differently. Surface temperatures behave absolutely differently; the film of oil in the Wankel engine acts as isolator. Engines with higher compression ratio have a worse surface/volume-ratio. The surface/volume-ratio of a Diesel engine is much worse than a gasoline engine, but Diesel engines are well known for a higher efficiency factor than gasoline engines. Thus we should compare engines with equal power: a naturally aspirated 1.3 liter Wankel engine with a naturally aspirated 1.3 liter four stroke reciprocating piston engine with equal power. But such a four stroke engine is not possible and needs twice the displacement for the same power as a wankel engine. The extra or "empty" stroke(s) we should not ignore, as a 4-stroke cylinder produces a power stroke only every other rotation of the crankshaft. In actuality, this doubles the real surface/volume-ratio for the four stroke reciprocating piston engine. [15]

The trailing side of the rotary engine’s combustion chamber develops a squeeze stream which pushes back the flamefront. With the conventional two-spark-plug or one-spark-plug system, this squeeze stream prevents the flame from propagating to the combustion chamber's trailing side in the mid and high engine speed ranges. This is why there can be more carbon monoxide and unburnt hydrocarbons in a Wankel's exhaust stream. A side port exhaust, as is used in the Mazda Renesis, avoids this because the unburned mixture cannot escape. The Mazda 26B avoided this issue through a 3-spark plug ignition system. (As a result, at the Le Mans 24 hour endurance race in 1991, the 26B had significantly lower fuel consumption than the competing reciprocating piston engines. All competitors had only the same amount of fuel available, because of the Le Mans 24h limited fuel quantity rule.[16])

All Mazda-made Wankel rotaries, including the new Renesis found in the RX8, burn a small quantity of oil by design; it is metered into the combustion chamber in order to preserve the apex seals. Owners must periodically add small amounts of oil, slightly increasing running costs--though it is still reasonable when compared to many reciprocating piston engines."

 

[gtx510]

*cough* *cough*
not quite, from the wankel page...
"In 1951, Wankel began development of the engine at NSU (NSU Motorenwerke AG), where he first conceived his rotary engine in 1954 (DKM 54, Drehkolbenmotor) and later the KKM 57 (the Wankel rotary engine, Kreiskolbenmotor) in 1957. The first working prototype DKM 54 was running on February 1, 1957 at the NSU research and development department Versuchsabteilung TX."

http://en.wikipedia.org/wiki/NSU_Motorenwerke_AG
"NSU Motorenwerke AG, (normally just NSU), was a German manufacturer of cars and motorcycles, which was founded in 1873. It was acquired by Volkswagen Group in 1969. VW merged the company with Auto Union, to eventually evolve into Audi as it is known today."

By 1969 NSU had made 2 cars with rotary engines and Mazda had made the Cosmo.


On a rotary I guess you could think of the side of the rotor as the "valves" since that's what let's air in and out. You could also think of the shape of the port (x-section as it enters the housing) as the cam profile.
And I don't remember any factory rotary using 3 sparkplugs per rotor, all of them just use 2. If you're interested about that look into the leading/trailing timing split, and negative split.

http://www.sportcompactcarweb.com/editors/technobabble/9808scc_technobabble/index.html
I think this is the right article? Some people think Mazda underrated the displacement and there's where the rotary's "magical" power comes from.

http://www.sportcompactcarweb.com/editors/technobabble/9912scc_technobabble/index.html
Dave Coleman from SCC says 2.6L for the 13b.