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Hi Roger,
I am getting exhaust fumes in my cabin on my Aeroprakt A22. My exhaust manifold is the type where the manifold attaches to the muffler with the ~ 2" springs. I guess it is sort of a ball and socket type connection. During my 5 yr hose change last week my mechanic inspected the connections and put some type high temp sealant between them. On my first test flight the cabin was clear of fumes and all I could smell was the sealant on the springs of the muffler connection and/or what was put between the manifold to muffler connection.

On my second flight the fumes were back again. I must get this corrected fast and at any expense. Is there any way to improve the seal between the muffler and exhaust manifold? The muffler is from 2007 with 500 hrs in a dry climate. Do the mufflers ever fail within causing excessive back pressure? My muffler does not have a heat muff on it. Everything is out in the open.

Your input will be greatly appreciated.

William Campbell
Fresno, CA.
  • Re: 912UL Exhaust leak

    by » 6 years ago


    A couple of things to check. The obvious one is cracks. You can do an easy pressure test right on the plane. Take a shop vacuum and tape the hose over the end of the muffler. Switch the shop vac hose from the suction side to the blower side. Turn it on and use some soapy water to look for cracks and leaks. You can do this before and after you adjust the muffler.
    If the springs aren't sprung enough and aren't putting enough pressure on the joint it could leak. The springs should have about 1 mm gap (fingernail thickness) between spring coils. You may need to also loosen your exhaust pipes at the head and move the muffler a little left or right to get the socket joints to line up straighter and seal better.

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


    Thank you said by: Andrew Dunning

  • Re: 912UL Exhaust leak

    by » 6 years ago


    Thanks Roger,
    I will inspect and pressure check as suggested.

    William Campbell
    Fresno, CA

  • Re: 912UL Exhaust leak

    by » 6 years ago


    Foxbat A22LS...owner here....600+ hrs..
    I tried sealant but it gets too hot.
    Tried high temp loctite anti-seize which I think works better and allows the muffler to move and seat on the pipes better during exhaust install.
    When installing the exhaust system keep the nuts on the header pipes at the head lose enough to allow some pipe movement. Install everything, including muffler, the grab the muffler and wiggle it around to seat and align pipes.
    Then start to tighten nuts evenly, head to head. Every now and then give the muffler a wiggle to ensure it is still seated and hasn't moved.
    Make sure the holes in the firewall are sealed.
    I always get some smell when at low throttle and/or decending......An aerodynamic aspect I think.
    I just turn to vents to full open at thst stage.

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