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Thread: How to fix exhaust leaks?

  1. #1
    McDaver63's Avatar
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    Default How to fix exhaust leaks?

    I have a couple minor exhaust leaks at the #2 and #3 exhaust manifold flange to cylinder gaskets. When I originally installed them I used Red High Temp RTV on the No-Blow gaskets. It looks like most of the RTV has burned off and now it is leaking. Any suggestions on sealing them up properly? I have read on this forum about folks recommending sealing with exhaust paste such as Permatex. Does that work on the exhaust flange gaskets?

  2. #2
    mmoyle's Avatar
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    Default Re: How to fix exhaust leaks?

    The correct repair is to shave the exhaust port face with a resurfacing tool. ACS sells them... The tooling is spendy...but safer and cheaper than pulling the cylinder/s for repair..buying nuts and through bolts....and making sure to use the correct lubricant mixture when torquing the cylinder base nuts.
    Mark M.


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  3. #3

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    Default Re: How to fix exhaust leaks?

    If the Cylinder surface is fairly good - usually the exhaust stack flange is the problem - it can be straigtened and the surface trued up with a flat file or a belt sander No-blow spiral wound gaskets are the best - torqued the exhaust nuts to no more than 150 in lbs to avoid re-deforming the flange.

  4. #4
    McDaver63's Avatar
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    Default Re: How to fix exhaust leaks?

    The cylinders only have about 30 hrs out of overhaul. When I installed the exhaust stack they looked perfectly flat at the mating surfaces. I torqued to the specs from Lycoming. One thing I did though because another A&P friend told me to do it was to put red rtv on the gaskets. From what I've read on other post that is not a good idea because it just burns off and can cause corrosion on the cylinders. I guess I'll have to drop the stack and see what's causing the leaks.
    Both optimists and pessimists contribute to society. The optimist invents the aeroplane, the pessimist the parachute

  5. #5
    deandayton's Avatar
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    Default Re: How to fix exhaust leaks?

    I usually retorque after 5 or 10 hours. I've found that I'm less likely to have an exhaust leak if I do this. At least that's my unscientific experience.

  6. #6
    Gilbert Pierce's Avatar
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    Default Re: How to fix exhaust leaks?

    Quote Originally Posted by deandayton View Post
    I usually retorque after 5 or 10 hours. I've found that I'm less likely to have an exhaust leak if I do this. At least that's my unscientific experience.
    I second that. I always retorque.

  7. #7
    McDaver63's Avatar
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    Default Re: How to fix exhaust leaks?

    I think I did try that on #3 cylinder. I'll give it a shot again on both the cylinders. Thanks.

  8. #8
    deandayton's Avatar
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    Default Re: How to fix exhaust leaks?

    I guess I wasn't clear. Once the gasket starts to leak, re torquing will probably not help. Clean the surfaces, make sure they look good, install a new blow proof gasket and torque to spec. I always use new gaskets and then retorque 5 to 10 hours after installing.

    However, if the mating surfaces are not smooth, clean and a proper fit none of this will prevent it from leaking again.

  9. #9
    rocket's Avatar
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    Default Re: How to fix exhaust leaks?

    The one alarm that goes off here is the word torque.

    It is difficult to accurately torque these nuts regardless of the nut used and tool. It is one of those feel it in your hands kind of torque things and if you were using your, or mine, calibrated Snap On torque wrench most likely you are under torquing.

    As one draws the exhaust flange tight using less and less wrench turn as the torque increases one can feel the subtle crushing of the gasket material and then when the whole assembly is properly seated. I use a liberal amount of anti seize on both the stud and inside the nut before assembling. I also have used RTV on the no-blow gasket without detrimental effect for 18 years.

    I never found a need to re-torque but I do get a socket on them every 100 hour inspection as part of my process.

    I do think re-torquing them at 5 hours to be a great idea and the idea of giving everything else under the cawl a good look after a few hours gives one that feel good flying thing.

    I have seen some poorly assembled exhaust parts installed by the less attentive cause all kinds of noisy and smelly truama


    Rocket

  10. #10
    McDaver63's Avatar
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    Default How to fix exhaust leaks?

    I went ahead and tightened the leaking exhaust flange nuts. I was able to get a bit of turn on each of them. Cleaned the gray soot off and took it up for a leak check. Found a little bit of fresh soot on #3. Looks like I'll be ordering some new gaskets. I know folks like to use red rtv on the gaskets but does anybody use automotive exhaust paste? I think I've read on the forum some used it but not sure if on the stack gaskets. Red RTV is only rated for 6 or 700F where exhaust paste is rated to 2000F
    Last edited by McDaver63; 08-07-2014 at 10:09 PM. Reason: forgot info
    Both optimists and pessimists contribute to society. The optimist invents the aeroplane, the pessimist the parachute

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