Impatient mistakes and damage control
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Thread: Impatient mistakes and damage control

  1. #1
    Junior Member Rollthelosingdice's Avatar
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    Impatient mistakes and damage control

    Ok, I really messed up big time. I had a stripped spark plug hole on my 75 cb500t so I bought one of those tap and helicoil kits for it. Well I brought the piston to the top of the cylinder and stuck a towel inside. As I was tapping, it got most of the way but not all the way inside which I assume it hit the piston. I put a little jb weld on the helicoil after cleaning all the metal shavings out of the hole and cylinder. I followed it with the spark plug.

    Here's where things get bad. The helicoil stopped with about a 1/16th sticking out of the hole and I knew that was because of the tap not going all the way through. So I backed out spark plug and it came out without the helicoil. I thought some how in my mind to just gorilla the spark plug in and hopefully the coil would get flush. Nope, it smashed the washer to the spark plug around the ridge of the coil.

    So at this point I used a hammer and punch to break out the washer and I bent over some of the helicoil. I already knew I was screwed so I just hammered it down, then the spark plug wouldn't thread in so I just used a 20v impact to get the plug in. I was just going to hope it would start. I get a few pops and a little smoke. So I'm looking on some advice on how to dig myself out of this mess.. Thanks for reading!

  2. #2
    Senior Member Rob Axel's Avatar
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    WOW... you did WHAT!?!?
    This is one for the records, never head of a impact being used in that manner.. not familiar with this motor, but i am familiar with messing things up...
    IMO.. to make sure you havnt done any further, possibly catastrophic damage.... pull the head..,have it repaired properly!!
    And I’m willing to bet they won’t use an impact to fix it
    krukster86, TOOLS1, Pops and 4 others like this.
    "Yes, my hands and nails have grease stains. I ride vintage!"
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  3. #3
    Senior Member doode's Avatar
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    Well, this sounds unfortunate. Now and then I make a series of bad decisions, and need to learn to realize when to take a break.

    Being said, possibly the right way would be to pay to have someone else fix this.

    If you're still up for some adventure, then pull the plug and helicoil, see if the tapped threads for the helicoil are okay, and if so finish the tap and follow instructions on install with locktite.

    Good luck!
    Bill H and Lefty like this.

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  5. #4
    Senior Member Boomer343's Avatar
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    Heli coils on spark plug threads are a patch job in my experience. And adding JB weld isn't going to help in the least.

    I repair heli coil spark plug threads by using an insert. The soft aluminum and already expanded hole from the heli coil allows the tap to be used without drilling.

    The inserts I use spec the use of high temperature silicon rtv on the insert threads and a suitable set time before running the engine.

    BTW how big of a hammer do you own? VBG
    doode likes this.

  6. #5
    Senior Member 76TWIN's Avatar
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    Yeah... I would say your only option would be to pull the head and inspect the damage and see if it can be repaired.
    Lesson learned here. Never use brute force on the engine.
    '76 CB500T Frankenbike
    '73 CL450 (basket case for now)


    Carpe narem.

  7. #6
    Senior Member pattyandrick's Avatar
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    Pack the tap with grease to catch the filings. Back off the tap and clean and repack every couple turns. Next time.
    You may have used a long helicoil where a short one was required.


    Sent from my SM-J320V using Tapatalk

  8. #7
    Senior Member CB450MWL's Avatar
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    My left cylinder plug hole is missing about three threads on top. I'm glad I asked here as I was contemplating insert or coil. It was suggested, not to worry about it as there are still plenty of threads left. I bought a plug chaser just to straighten the existing threads, greased it up and got it started straight and ran it in and out and haven't worried about it since. I do have a big hammer and little patience though.
    ancientdad and Rob Axel like this.
    1972 CB450 K5

  9. #8
    Junior Member Rollthelosingdice's Avatar
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    I might try to extract the helicoil with a big easy out before I pull the head. Thanks for advice.

  10. #9
    Senior Member TOOLS1's Avatar
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    If it is a heli-coil and not a Timesert you should be able to take it out with a pick and needle-nose pliers.
    TOOLS
    Alan F. likes this.

  11. #10
    Junior Member Rollthelosingdice's Avatar
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    Ok I went and bought a large easy-out and I managed to get the helicoil out, woah that felt good! I re-tapped the threads and put a new helicoil in with the proper high temp rtv silicone. It sits flush in the new holes with a brand new pair of spark plugs! Wish me luck when I start it tomorrow

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