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Exhaust Manifold

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  • Spk99
    • Oct 25 2018
    • 165

    Exhaust Manifold

    Quick question if I may guys?
    Im currently undertaking a rebuild of my 352.
    I probably shouldn’t be as I have no idea what I am doing but hey, when has that ever stopped me
    Anyway whilst I’m waiting for parts to arrive I’ve been cleaning up some items.
    The below photos of my exhaust manifold. Is this the exhaust gas control valve? It appears to be stuck open.
    Looking at the workshop manual, it looks like a spring is missing?
    Does this look like someone has modified this to stay open and if so, is that a problem?
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    This gallery has 2 photos.
  • TZTony
    • Jul 4 2020
    • 57

    Yes, that’s your heat riser. It’s job is to close when the engine is cold to route warm exhaust under the manifold, to help warm up the carb. Once the engine heats up it opens, allowing the exhaust gas to pass through and exit out the pipe.

    It should indeed have a spring on the baffle plate which, much like a stock choke, expands with heat, causing the baffle plate to open. These frequently rust up or become frozen with built up carbon, and are a common point of failure. If stuck closed, exhaust never vents fully, causing overheating and leaking fumes in the engine bay. If stuck open, it simply does not help pre-heat the carb.

    A common “fix” is what one of your previous owners did: rig it to remain open. Since these classics are often used only in nice warm weather, there’s little benefit to a working riser, as the engine heats relatively quickly in mild temperatures. It’s really only if your climate is cold and/or the car is used in the winter that the heat riser becomes a handy component.

    That said, since you have the hard part done (it’s apart), now might be a good time to fix it. The suppliers sell replacements or, if you don’t care about extra heat a functional riser provides, a cheaper option is the spacer that the suppliers also sell. It’s basically the outer housing (minus the baffle plate) to seal the system from leaks and allow the exhaust gas to always pass through. The cheapest option would be to reuse what you have, keeping the baffle rigged in the open position, or remove the baffle plate from the one you have and weld up the holes for reuse. All up to you.

    Mine is broken too - it has no spring, and sometimes clinks open and shut in the exhaust breeze. But I’m afraid to tackle removal for fear that I’ll break the corroded bolts and then have to yank the exhaust manifolds.

    Good luck with your rebuild and kudos to you for taking it on!


    • Spk99
      • Oct 25 2018
      • 165

      Thanks for that Tony. As I’m in Australia, seems little point messing with it then. I think
      ill leave as is if it doesn’t affect how the engine runs. Let’s just hope I can get it to run again