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For the preservation and enjoyment of 1928 to 1931 Indian Scout Motocycles
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Loose Inlet Nipple

  • 04 Nov 2021 6:16 AM
    Message # 12098733

    Just had an intake nipple screw out of 45" reproduction barrel with manifold nut.  Thinking of how to retain nipple back in? Just wondering what temperature might be in that area?


    Malcolm Clark

  • 05 Nov 2021 3:46 AM
    Reply # 12101542 on 12098733
    Tim Raindle (Administrator)

    Hi Malcolm, the inlet nipples on the originals are pinned in place with a small rivet. Some guys just use a thread locker there in repros, but I have always pinned them in as per original. Will try and dig out some pics to help explain, may take a while as I am currently out of the shopping visiting the UK.

    I use a length of welding rod, somewhere around 0.098 ", drill a hole through the screwed in cylinder and nipple, that size, then make a rivet to fit. by slightly countersinking the hole on either end, the inside one with a small burr tool on a dremel, you can fit a handmade rivet from the inside, drive it snug with a close fitting slightly tapered mandril, and peen the outside into the countersunk hole in the cylinder, carefully. 

    Make the rivet to fit by drilling a hole in a piece of solid stock the correct length, counterinking the top, and peening over the top which will create the correct shape, and removing it from the block. May take a couple of tries to get it perfect, but cost not high, and best to have a nice fit for the actual cylinder. 

    Thought I did an article in a wow a while back, if not I should. Pics make process very clear. 

    Have also seen small grub screws used here as well, smaller hole the better tho,in my humble.

  • 07 Nov 2021 8:40 AM
    Reply # 12107413 on 12098733

    There is an article in VirtualIndian  by Tom Cotten that gives some good tips, one is the anvil to support the nipple from the inside. AND checking for leaks is essential, both before drilling and after riveting the inlet nipples.

    A grinding fixture (dummy thread insert to protect the threads and a plug that slides in that, with a rim slightly wider than the nipple rim) can be made to grind the cylinder surface perfectly flat and perpendicular before.

    Note that threads is never sealing as there is always a gap between the male and female threads (if dry, without sealing compound). it is the rim that must be tight, and rivet. A few threads on the nipple close to the rim must be absent, as seen in one of the pictures, in order to avoid threads pull up and distort the cylinder rim surface when the nipple is torqued down.

    One way torqueing the nipple down is to use a turned down muffler tube expander. The cylinder can be heated a bit before threading the nipple in but keep the temp below the temperature that would settle the thread sealer.

    But don't overdo when tightening down! No hammer tapping. Cylinder threads can strip! it is fine shallow although wide threads. One time medium torque to shape the threads if new, then back out and torque again a similar or maybe medium-hard ompfh should be enough.

    Picture shows different eccentric anvils and a special clamp to pre-shape and compress the rivet butt before final fine-tune riveting. The rivet should fit snug in the hole and protrude 1,5 times the diameter before forming a shallow dome about 1/2 height of the rivet diameter. A tall dome is not better. The inside head is deforming as well so keep the anvil tight during hammering. A drop of anaerobic thread locker before putting in the rivet wouldn't harm, in my opinion.

    If the attempt is unsuccessful, the rim on the nipple can be ground or turned thinner in order to turn the nipple a bit deeper, to shift the position of the already drilled hole, and drill a new hole in the nipple.

    P.s. A medium-hard ompfh is a calibrated elbow torque on the “uggadugga” scale. In German Torque it is almost one Guttenuff.

    7 files
    Last modified: 07 Nov 2021 2:53 PM | Carl-Erik Renquist
  • 08 Mar 2022 12:55 AM
    Reply # 12647264 on 12098733

    Thanks Tim & Carl-Erik for your detailed responses & the link to Virtual Indian. My apologies for my late reply since the barrels have been nickeled & assembled I am leaning towards low strength thread lock. This motor was assembled prior to myself purchasing it, then it had sat for 10 years. Upon starting it I realised things were not airtight. Once again thank you for your experienced reply. 

    Kind regards, 

    Malcolm Clark 

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