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Thread: Exhaust manifold stud help

  1. #1
    Join Date
    Jul 2021
    Location
    California
    Posts
    17
    My Cars
    '97 328i Convertible

    Exhaust manifold stud help

    I fucked up, went to replace one of my exhaust manifolds because it has a cracked flange. The studs came out with the nuts for the most of them. I tried to be cheap and reuse the hardware. when I was putting everything back together, I didn't notice that the studs on a couple of them didn't thread in properly and they got stuck at about 1/4 of the way into the head. then it's was just the nut that's started turning. When I went to torque them down to spec the threads ripped out.

    I have about 3/4 of usable threads, but I cant get the stud started in by hand because of the mangled initial threads.

    Other than completely drilling out and helicoiling the threads, what can I do? I'd like to save the threads that are still there and maybe clean up the 1/4 mangled part.

    Since it's one mangled thread on each manifold I would have just ignored it but these studs hold the SAP tubes and it would only be one of the 2 nuts holding it on. definitely causing an exhaust leak.

    Also it's extremely limited space, if I had to drill it out Im not sure how I can fit the drill bit + the right angle attachment + keeping it straight.

    Here are photos of said threads
    https://imgur.com/a/xvY8bt5

  2. #2
    Join Date
    Dec 2022
    Location
    NH
    Posts
    137
    My Cars
    M3
    If you can use a thread tap to straighten the mangled part you'll be able to use the rest of the thread. If you can't get a tap or other tools in there, the head will have to come down.

  3. #3
    Join Date
    Jun 2005
    Location
    New England
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    25,402
    My Cars
    F90 M5; E36 M3 Turbo
    I would use a tap just for the pulled threads at the start but not run the tap all the way down. Switch to a thread chaser for the hood threads if you want to clean them. This is delicate work because you must hold the tap perfectly square or you might cut at an angle and end up cross threading. There should be enough room with the manifold out. Hopefully you won’t end up having to drill out and helicoil or similar.

  4. #4
    Join Date
    Jul 2021
    Location
    California
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    17
    My Cars
    '97 328i Convertible
    Update, i tried the method suggested and it worked great. But instead of buying a thread chaser I ended up using a double nutted stud that I took off the car and went very carefully. A couple turns then full backed out and cleaned the hole with compressed air. So grateful I didn't have to helicoil

  5. #5
    Join Date
    Jun 2005
    Location
    New England
    Posts
    25,402
    My Cars
    F90 M5; E36 M3 Turbo
    For future use, the advantage of the thread chaser is that it has slots down the sides so the threads are not continuous. This allows debris to pass. Using another bolt can mess up the threads. If you do it that way, go 1 turn, remove, blow out, and repeat and the risk is lessened though blowing often won’t remove wisps of thread still connected to the thread.

  6. #6
    Join Date
    Jun 2009
    Location
    washington dc
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    8,679
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    Avus Cosmos Calypso!
    Glad you got it sorted. Always finger screw bolts in to finger tight while keeping the axis orthogonal.

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