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Engine oil for rotary

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I have a question about the aircraft conversion for the rotary. You have to add two-stroke lawn mower oil to the fuel. Doesn't this make the engine burn "dirty", thus causing carbon deposit build-up in the combustion chamber and exhaust port areas. My understanding is that enough build-up can cause pre-ignition. Does anyone have information on this?

Jack Kretmar

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On a "normal" engine, the piston rings are lubricated by oil splash from the crankcase. In the rotary, the apex seals, which perform a similar function, also need lubrication. Because the wankel design precludes oil splash on the apex seals, oil needs to be somehow introduced into the combustion chamber to lubricate the seals. Mazda used several methods to do this, all of which take oil from the sump and inject it into the combustion chamber. This HIGH detergent motor oil does NOT burn cleanly and causes the problems you describe. By the time they got to the third generation RX-7, they were calling for a special grade of oil(SH 5w-30??) which was hard to find. Two stroke oil is designed to burn cleanly with minimal deposits. Probably Mazda marketing thought that a separate oil tank for two stroke oil would not go over well with customers.

By removing the oil injection pump, you eliminate a failure point and some weight. If you really don't like the idea of premixing, there is a device available that feeds the oil injection pump from a separate tank that can contain two stroke oil. I also heard of one project where the stock oil injection was to be used and the sump filled with LOW detergent aircraft oil. It was claimed that because air cooled engines have a wide temperature range and large internal clearances, more oil than is desirable gets into the combustion chamber, so this oil is desiged to burn clean also. I think that needs to be verified by someone familiar with oil chemistry.

One of the best resources is Tracy Crook's company, Real World Solutions. He has a conversion guide that should answer most other questions you may have

"We choose to do these things not because they are easy, but because they are hard."


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Kinda strikes me as "interesting" that those of us who pump oil from the ground directly into a lycosours (esp. in a rented plane <g>) have this issue with adding oil to the rotory. I know you were only looking for information, me too. I am only slightly ahead of you in my quest for knowledge, on this topic anyway.


I think Rob Johnson (www.RobJohnson.com) has a nice little essay on his Velocity site....oh, I just checked his site is down. Sorry.


I believe he makes referrence to using aircraft oil and it being as good or better for the hmmmmmmm engine. I may have the webpage saved somewhere. If I find it and his site stays down, I will post it.


BTW, if I was not convinced to use a rotary before, I am now. I got a test RIDE (no, not drive...that car hasn't arrived yet) in the new RX-8. OMG! All that stuff they say about smoothness is complete truth. Dealers have been instructed to state 207 hp on the auto and 247 on the standard transmission. Very Kewl. The car is only ok, the engine is wow. When they become available it is my understanding a "long" block will be $5757.00 USD, new.




All the best,



Christopher Barber

Velocity SE/FG w/yoke. Zoom, zoom, zoom.



Live with Passion...

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