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Thread: '48 Chief. Spark plug thread Q ?

  1. '48 Chief. Spark plug thread Q ?

    New to Indians so explain this. I went to tighten one of the spark plugs and it appears whatever the plug is threaded in to is turning also. Looks like a bushing? I see on Jerry Greers page item #4 says there's an insert there
    https://www.jerrygreersengineering.c...y=1948&m=Chief
    Is that a repair or is that normal from the factory ? I stopped tightening because it didnt look/feel right.

  2. Re: '48 Chief. Spark plug thread Q ?

    Aluminum cylinder heads commonly have a threaded brass insert for the spark plug. If there was no insert, the aluminum would tend to strip-out. Pinned brass inserts are best, as they tend to stay put. Inserts that are not pinned can come out, and this can be a big hassle, if it involves a failed spark plug on the side of the road. I have never seen a pinned insert come out, but I imagine that in some instances, the pin could shear and allow the insert to come out. Some original heads have inserts that are not pinned. I think that the new reproduction heads that Jerry Greer sells do have the inserts pinned. The photos below show the pinned inserts and the insert from the underside of the head. In order to properly pin the inserts, the heads should be removed. Any reputable machine shop could do it. The pins are brass. Even with the inserts, the original short reach spark plug can tend to strip-out the insert threads. Long reach spark plugs can take advantage of all the insert threads. If some of the spark plug threads extend below the bottom of the insert, those threads should be removed from the spark plug so that they don't become carboned-up which makes plug removal difficult.

    Aluminum cylinder head with a brass spark plug insert by Steven Bailey, on Flickr

    Cylinder head with spark plug insert clearly pinned A by Steven Bailey, on Flickr

    Cylinder head with spark plug insert clearly pinned B by Steven Bailey, on Flickr

  3. Re: '48 Chief. Spark plug thread Q ?

    I'm guessing mine is not pinned then. A part of me believes it'll bottom out and start to tighten up but I dont want to risk doing any damage. Another idea I was thinking is extract it a touch and add a dab of Loctite an re tighten to where its flush with the head? Any of these make sense ?

  4. Re: '48 Chief. Spark plug thread Q ?

    Hi,
    The cylinder head temperature could reach 350 degrees Fahrenheit or even hotter, so most common Loctite formulations won't help much. There are some extreme temperature thread-lockers - made for turbocharger applications, but I haven't tried any of them. The best thing other than pinning the insert would be to tighten the insert - but you can't really use a spark plug to do it; as removing the spark plug would likely remove the insert again. The tool to use to tighten the insert would be a threaded rod with the same thread as the spark plug, and a jam nut to sit against the outside face of the insert. Using the tool, with the jam nut against the insert, the insert could be tightened down more than you could do it with a spark plug. After the insert is good and tight, loosen the jam nut and then unthread the tool. This process is probably similar to what a machine shop would do prior to pinning the insert. If you want to give the insert a little more bite, do the tightening job with the head warm. After that job is done, only install or remove the spark plug when the engine is cool; which will reduce the chance of the insert coming out again. All of this might get you by until the heads are pulled for some reason, and then the inserts could be pinned. Spark plugs are usually only tightened to 25 foot pounds, so if you can get the insert tightened to something like 50 foot pounds, you should be good enough - at least for a while.

  5. #5

    Re: '48 Chief. Spark plug thread Q ?

    FWIW, I had an insert blow out still threaded onto the plug... probably 15k miles ago, so I replaced the insert with a new one from Greer's as the threads in the aluminum were still good. I used Loctite 2422 rated to 650 degrees F. The Loctite gave me peace of mind, but probably that's all it did! Checking the plugs is now on my pre-trip inspection list, and last time I changed plugs the insert came out with the plug again in spite of using never-seize on the plug threads. One thing about the Greer's inserts, they have a hex head on top so they don't sit flush with the head, turns out that feature comes in handy to install the insert as well as when it's stuck to the plug... you can get it off and re-install it without munging up the threads!
    1946 Chief - take apart and put back together
    101 Scout - building stage

  6. Re: '48 Chief. Spark plug thread Q ?

    Pisten-Bully, tried to PM you, but I'm getting a message that your mailbox is full.

  7. Re: '48 Chief. Spark plug thread Q ?

    Thanks for the advice guys, much appreciated ��

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