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Rotary engine question

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:) I'm posting this in the general forum. In aircraft conversions of the rotary engine, you have to add two-stroke lawn mower engine oil to the fuel. Can this make the engine burn "dirty", causing carbon deposit build-up in the combustion chamber and exhaust port areas?

It is my understanding that carbon build-up can cause pre-ignition.

Is this a factor, and if so, what can be done about it?



Jack Kretmar

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No. Weed eaters and chain saws use a 40:1 mix. Mazdas use closer to 150:1. Additionally, 2-stroke oil is ashless. Motor oil is not recommended and in fact is discouraged. The Mazda automobile applications have a little pump system that injects a little motor oil out of the pan. Engine failures, far from being caused by deposits, are more likely if the oil injection system fails. That's why rotary powered airplanes mix it with the gas. Also, the mixture from the injector is not at all uniform. Motor oil, which is only marginally suitable but is the source in cars, works fine. 2-stroke oil, which can be bought for a maybe 5 bucks gallon, is great. Marvel Mystery oil is also popular. For perspective, 1 oz (carry a measuring cup with you) per gallon gives you a 128:1 mixture; one quart would work for a cozy tank full. Different folks have different ideas ranging from 120:1 to 180:1 mixture. Join Tracy Crook's Rotary list and surf the archives.

...Destiny's Plaything...

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