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Thread: Those Pesky Exhaust Studs

  1. #1
    Administrator Steve Pierce's Avatar
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    Default Those Pesky Exhaust Studs

    So I got a Tri-Pacer in for it's annual inspection yesterday afternoon. 3rd annual I have done on this particular airplane. Check compression and drained the oil before going home last night. I had noticed that it had new spark plugs but when I pulled the lower plug on #3 first thing this morning I noticed this.
    IMG_20180710_100935.jpg

    I looked at the exhaust flange and saw this.
    IMG_20180710_101200.jpg
    I inserted a new stud and when I started tightening the exhaust nut it was obvious I was pulling the stud out of the cylinder head. I started removing the exhaust pipe for #3 and #4 which is a bear to get out of the muffler because the coss-over pipe hits the steering horn on the nose gear when you rotate it down enough for the flanges to clear the cylinders. It was easier to remove the exhaust pipe to #1 and #2 and get clearance to get everything out. Since I had both pipes off it was easy to inspect the muffler. HeliCoiled the exhaust stud hole that had the missing stud. Get everything back on and the muffler clamps to pipes torqued prior to tightening the exhaust flanges to the cylinders when the front exhaust stud on the same cylinder started pulling so pull everything back off and HeliCoiled it. Got the whole system back on again and noticed I had one new exhaust gasket and three old ones. My helper put the old one on $4 when he was helping me get the pipes on the studs. Was able to loosen that pipe and get the new gasket on but when I started tightening the outside exhaust nut I could feel it starting to pull so I stopped and was able to double nut it and get the stud out with the pipe still installed. Then I was able to get an over sized stud in and the nut torqued without pulling the pipe back off. It felt like a Monday and reminded me why I hate the exhaust AD on the these airplanes.

    I documented the whole exhaust stud fiasco in pictures and comments in this Google Photo Album if anyone is interested.
    https://photos.app.goo.gl/F871mY9pPeFP1RHu6

  2. #2
    JPerkins's Avatar
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    Default Re: Those Pesky Exhaust Studs

    Why do you suppose they're so notorious for doing that? Design flaw? Or getting over torqued?
    Jason Perkins

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    walt.buskey's Avatar
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    Default Re: Those Pesky Exhaust Studs

    Boy, Steve, and I thought I was the only one (not really) who had those days where everything I touched turned to #@!#..... Good on ya for hangin' in there!

  4. #4
    Administrator Steve Pierce's Avatar
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    Default Re: Those Pesky Exhaust Studs

    Quote Originally Posted by JPerkins View Post
    Why do you suppose they're so notorious for doing that? Design flaw? Or getting over torqued?
    I believe it is the same reason cylinders crack, heat cycles and also getting retorqued every 100 to 50 hours during exhaust AD inspections. Another reason I dislike rebuilt cylinders at overhaul.

  5. #5
    smcnutt's Avatar
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    Default Re: Those Pesky Exhaust Studs

    You mean there should be an exhaust stud in EVERY HOLE? I mean there's 8 in the whole system and 7 out of 8 isn't good enough? Jeez, you're such a perfectionist.

    At least you didn't have to resurface the exhaust port. With that much blowing past it is surprising it didn't eat it away.



    Sent from my SM-T350 using ShortWingPipers.Org mobile app
    “Common sense is in spite of, not the result of, education.”
    ― Victor Hugo

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    Default Re: Those Pesky Exhaust Studs

    Don’t forget to check flatness on the flanges and erosion on the mating surface of the cylinder. Constant retorquing causes the Ganges to bow and not seal against the gasket


    Sent from my iPhone using Tapatalk

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    Administrator Steve Pierce's Avatar
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    Default Re: Those Pesky Exhaust Studs

    I think the reason there was no erosion is it got caught early before it got bad. Last annual was less than 70 hours ago. Brings up a good point to look for exhaust stains on pre-flight. Can cause erosion of the cylinder and the exhaust pipe which can get expensive. This tool comes in handy when that happens to the cylinder.
    100_2073.jpg

  8. #8

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    Default Re: Those Pesky Exhaust Studs

    Yeah, wish I had one of those! They are expensive, but can save the day when the surface is eroded. Last I looked, the company that made them is no longer in business, or at least no longer marketing them. What’s the name of it?


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  9. #9
    Administrator Steve Pierce's Avatar
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    Default Re: Those Pesky Exhaust Studs

    Aero Grinder. Yea, the guy that made them works on King Airs now. I bought mine at the fly market at Oshkosh several years ago for $500. I have loaned it to members here before.

  10. #10
    Gilbert Pierce's Avatar
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    Default Re: Those Pesky Exhaust Studs

    Sutton exhaust end those pesky problems on my airplane. Wish my customers would go that route.

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