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  1. #1
    soarrich's Avatar
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    Cox .049 Dragonfly

    I have a Dragonfly engine that I'm having trouble with. Every time I get it to run, 2 seconds, it develops an air leak between the crankcase and the tank. Is this a common fault? I tried retighting it to no avail, so I put some Hi-temp RTV on it in hopes that will seal it, I'll test this later today to see if it worked.
    Rich Border AMA 77727
    Sig Kadet Brotherhood #2

  2. #2

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    Cox .049 Dragonfly

    The Dragonfly was (I thought) the perfect engine when they first came out. It may just be me and some kind of bad Ju-Ju but I've had a lot of trouble getting them to run steadily.

    If you're having trouble with case/tank leakage, did you flatten the rear of the case with some 600 wet/dry paper on a piece of glass to remove the lumps around the tapped holes? This has to be a standard procedure on all reedies to get them to seal. I assume you're using the paper gasket as well? It seems like they stopped using the paper gaskets later on but I think they're mandatory.

    Also, I think the venturi opening is too large for consistent running on the D/Fly. Fellow Cox-a-holic buddy Lester Goldsmith came up with a cure that seems to smooth 'em out. He stuffs a short length of medium (I think) silicone tubing down into the venturi opening which reduces the dia. enough to really improve suction. I've had a couple of 'em with a good TD piston/cyl. installed that would really scream at enough revs to properly use that big venturi opening but they were still very touchy. I gave up and switched back to detuned TD's for my sport flyers.

    HTH!
    \"He who dies with the most good Cox engines wins!\"

  3. #3
    soarrich's Avatar
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    Cox .049 Dragonfly

    Dickeybird
    Thanks for the info. I already used the RTV, but if that doesn't fix it I'll do the 600 paper thing.

    I modified the throttle muffler, I'm going to run it bare, then with a stock muffler, then my modified muffler. I may be able to barrow a db meter to get sound readings to go with my tack readings. I still have to turn a exhaust outlet for my muffler, I'm hoping the flexible body will help quiet down. Any idea on how big the exhaust outlet should be?
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    Rich Border AMA 77727
    Sig Kadet Brotherhood #2

  4. #4

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    RE: Cox .049 Dragonfly

    After countless hours of Cox Drangonfly 049 R&R, I discovered a CRACK, in the Suction nipple Area. No way the engine could pull any nitro fuel. Then I switched to WHITE Dragonfly 049 style. Then, I discovered a leaky rubber seal on the needle valve. Now, at least it runs continuouly. I hope to get the muffler throttle to work, and then a diesel conversion. After that, I will use a diesel with a carburetor. Hope for the best.


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