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Exhaust nut and gasket question

Discussion in 'Boxers/TR/M' started by JohnMH, Nov 9, 2025 at 1:34 AM.

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  1. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,891
    Bologna
    #1 JohnMH, Nov 9, 2025 at 1:34 AM
    My 91 TR has an annoying minor exhaust leak somewhere that is hard to trace. The sound goes away when the engine gets warm. Exhaust system has been rehung and realigned, the large gaskets between sections are in good condition and tight. Unless a manifold pipe has a hole (I hope not) I suspect there is one or more leaks where the heads and manifolds meet.

    The copper plated 13mm nuts and metallic manifold gaskets are original and could be tired. I am going to try to source 24 replacement copper plated nuts like the originals - from memory I recall they are slightly concave and scalloped on the surface where they meet the manifold.

    I can also get new high quality copper exhaust manifold gaskets locally where I am; Modena Motori is not too far from me. They look a little thicker than the silver originals.

    One question - does anyone use any type of sealant on the manifold gaskets? I really hate this ticking sound when I start the car.
     
  2. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
    9,664
    southwest Germany, France ( Alsace ) and Thailand
    Full Name:
    romano schwabel
    #2 turbo-joe, Nov 9, 2025 at 5:33 AM
    you may use exhaust assembly paste. this I use when I put 2 silencers together, but never used it for the gaskets between the manifolds and the head but I think this would work. give it a try.
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    and the 8 mm nuts are also available with size 12 mm and also with 10 mm ( very rare ) for the tool. go to a motorcycle shop, they have. but be carefull, most bikes have other thread, instead of the M 8 x 1,25 only M 8 x 1,00. but there are also available M 8 x 1,25 Image Unavailable, Please Login Image Unavailable, Please Login
     
  3. EDoug

    EDoug Formula Junior

    Apr 19, 2005
    292
    Southern Florida
    #3 EDoug, Nov 9, 2025 at 9:26 AM
  4. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    37,384
    Cowboy Capitol of the World
    Full Name:
    Brian Crall
    #4 Rifledriver, Nov 9, 2025 at 9:33 AM
    Never used sealant. In fact I have never even replaced the gaskets at the head, I reuse them and since 1985 on hundreds of cars never had an exhaust leak.
    I'd look for a damaged surface or a cracked weld. Does it have air injection? Those parts are prone to leaking. Get an automotive stethescope and remove the probe. They are outstanding at pin pointing exhaust leaks.
     
    Steve Magnusson and Mirek like this.
  5. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    1,891
    Bologna
    #5 JohnMH, Nov 9, 2025 at 1:15 PM
    Euro spec 91 car, so no air injection. Car has no precats, runs test pipes.

    The pipes that connect the manifolds to the test pipes have no probes, but have some bungs on them, they seem welded shut.

    Heads are straight - the surfaces are clean and straight (from a good machine shop in Modena).

    I keep thinking it is the exhaust gaskets at the head and maybe a worn or stripped thread on one or more old exhaust nuts.
     

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