The 101 Association, Inc.
For the preservation and enjoyment of 1928 to 1931 Indian Scout Motocycles
"You can't wear out an Indian Scout"

Intake Manifold Question

  • 14 Apr 2020 6:11 PM
    Message # 8900282

    Can anybody tell me the purpose of the appendage threaded into the top side of my intake manifold?  It doesn't appear to have a through-hole, but it's pretty cruddy and I haven't tried to see if there's a port to the interior of the manifold.

    Can the cones be removed from the manifold?  Mine seem to be pressed on there pretty tight and I don't want to be too forceful.



    1 file
  • 15 Apr 2020 3:41 AM
    Reply # 8900871 on 8900282

    It looks like a connection to fit a vacuum gauge.

  • 15 Apr 2020 8:45 AM
    Reply # 8901146 on 8900282
    Tim Raindle (Administrator)

    Seen a few of those plugs, yup, always assumed a vacuum gauge too. Not sure as I can quite see the point. Happy to be enlightened. 

    Removal of nuts/cones :-

    Same as everything else, softly softly catchee monkey.

    Try penetrating oil and if that doesn't work, a little very light heat. Might be worth leaving them to soak in a nice diesel/kerosene type mix. You will have to tap the nuts gently round the edges in different places. New brass cones are cheap, and the alternative option is the plastic type peak seals, which are around 40 bucks a pair, and work very well, but can sometimes be a one use only item. 

    If you are happy to replace, it may be easier to find or turn down a correct sized piece of tube that will fit over the manifold and move the cones back to free them up, then spin them off once free, as the nuts are designed to tighten them on, so tapping in that direction is always going to be harder.

    If there is no damage to the outside diameter of the manifold ( often worn and distorted thru over tightening and use) you may well be able to reuse the originals if the sealing face where they seat  against the manifold is flat. You can reface them carefully if they are only lightly damaged.

  • 15 Apr 2020 8:04 PM
    Reply # 8902465 on 8900282

    I would advise if it is not absolutely unavoidable to remove the cones to leave them be. Only if you have to replace the nuts or have leaking cones, then it is worth doing. And any time when reusing old cones, use liberal dub of pipe goop to seal. And bubble test. Always do bubble tests as soon there is an opportunity.

    The reason is that the 45ci intake manifold is thin as a blade at the spigots and as the cones are of brass, the nut has to be tightened hard in order to clamp and seal, and that distorts the thin spigots. Add to that the expansion and contraction from the cylinder heat and vibrations does wear a groove in the spigots, even more so if the carburetor is unsupported.

    Never ride with a unsupported carburetor, some version Scouts did not have that from factory. Make a support if there is none. It is danger both from fire hazard of a sagging leaking carb, and risk of engine seizure from air leaks.

    As the spigots are thin, there is little to no material to turn off to make a smooth surface for new cones, so it is almost always needed adding material (hard solder brass) or cut off entirely and make new tubes to press in the manifold body. 37ci manifold spigots can be a bit thicker but do wear in the same way.

    So restoration of the spigots is problematic but that is almost always needed if old brass cones are removed as their position is altered and they become distorted, and especially if they are replaced for new because new cones are really difficult to get to seal in the grooves that the old cones has made...

    If a decision to restore the spigots is made and the spigot surfaces are round and smooth then, is what I think is best, to use the new plastic cones that is reusable and does not require the nuts to be torqued as hard in order to seal safely. If used on rough surfaces they don't always seal well.

    6 files
  • 15 Apr 2020 9:18 PM
    Reply # 8902512 on 8900282

    The thing on the manifold looks more like a spring hook of some sort, maybe for a return spring for the throttle??

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