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Spark plug cross threaded

Discussion in 'Mechanic and Repair' started by Scott's Lawn Maintenance, Mar 5, 2013.

  1. herler

    herler LawnSite Fanatic
    Messages: 5,139


    Because you think it did this, and I've done that...
    Doesn't work that way.

    First step: Diagnose the problem.
    For example it could be there's simply some dirt caught in the threads.

    The first thing to do then is confirm whether or not you actually stripped the threads.

    I would like for you to slowly and carefully back that spark plug out of the engine and I hope you have a keen eye but pull a magnifying glass if you need to, certainly you want to work in a well-lit area... Because I want you to glue an eye to the threads of the spark plug as you are working it back out of the engine and watch carefully as to see if you spot any metal shavings whatsoever falling or coming out, that would be a pretty sure sign of cross-threading.
    Hope there are none.

    Then, after you get the spark plug out, inspect the threads carefully and see if you can spot the signs of crossed threads.
    Hopefully, you can't.

    Ditto for the spark plug hole in the cylinder head of the engine, see if you can look at those threads.

    Last but not least, throw that spark plug away just to be safe.
    And get a brand new one, gap it to .025

    Now you may need to get some compressed air to blow out the hole, it could be there's simply some dirt caught in the threads.

    And now get a 3/8" rubber hose and attach that to the wire tip end of the plug, where the ignition wire would go, attach a rubber hose to that end so that it dangles from a foot long piece of the hose.

    And use that hose to carefully thread it in to the engine.
    It should thread in almost all the way with just the rubber hose.
    Only towards the end should you need to use a tool.

    Once you get used to the effort it takes using the rubber hose you can probably go back to threading it in by hand, but the rubber hose trick was shown to me by an old man who told me, son, you strip another one of them and you may have to buy a new engine, so use the hose trick. Ya, I did, took those wise words as future advise.

    Fortunately in my case it was just dirt in the threads.
    And truthfully your worst case scenario wouldn't be a new engine, but possibly a cylinder head.
    You can try your luck with helicoils and thread chasers, but if the above doesn't work...
    In the worst case you're likely looking at replacing the cylinder head.
    Yeah, and one with the valves already installed costs $30 or so more lol
    But diy'ers warning - those valves are a royal pita.
    They are, hahahaha

    Good luck
    Last edited: Mar 6, 2013
  2. Grant11

    Grant11 LawnSite Senior Member
    Messages: 358

    If all of this stuff doesn't work out I would pull the head off and bring it to a machine shop. The guys I bring stuff to are great and they do everything they can to help me out. They have the special tools and knowledge on how to fix stuff that an average do it yourselfer cannot do. Good luck
  3. Scott's Lawn Maintenance

    Scott's Lawn Maintenance LawnSite Senior Member
    Messages: 326

    Thanks everyone for your advice. I picked up a spark plug thread repair kit at auto zone and following the instructions was able to make the repair .
    Posted via Mobile Device

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