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exhust tube cracking and seperating

in General Tech Discussion 14 years ago
i maintain a 912ULS on a TLA-2000 S3. we have had the #4 cylinder exhaust tube crack three times now about an inch from the knurl on the engine side of the tube. Can't find any vibes anywhere. trying to get new tube but would like to find out what might be causing.
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  • Re: exhust tube cracking and seperating

    by » 14 years ago

    I have no idea why it cracked the first time but the other 2 times was caused by what ever caused it the frist time and the welds, anytime you weld something, especially thin wall, it gets brittle from the heat of welding, the way to cure that is to heat soak it at 400 deg's for a hour or longer to anneal the part and then let it cool in the heat source overnight. There is a down side to doing this, the part that being annealed can relax and alignment can be a small problem but it's nothing that can't be cured with a few swear words and a hard drometer soft hammer.

    One last thing, I would suggest that a TIG welder be used, if it was welded with a TIG,,,find another welder.
      
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  • Re: exhust tube cracking and seperating

    by » 14 years ago

    Howdy Karl,

    There is no way to be absolutely positive about why the exhaust on you particular plane broke. I can say that there are a few thing to consider.
    First, is the exhaust pipe in question under stress from trying to pull it in line with the muffler for alignment?
    Second, lube the end of the exhaust pipe where it goes into the cylinder and at the muffler knuckle with a small amount of copper anti seize to keep it from binding.
    Third, don't over tighten the exhaust flange. (110 in/lbs)
    Forth, excessive vibration. balance the carbs, do a prop balance, static and dynamic. You can't always feel a vibration that causes damage.
    The first may have been a fluke, but the others may have been a poor weld or too much heat from the welder.

    Start with a fresh pipe and use a good Tig welding person.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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