Small bubbles at spark plug thread

Discussion in 'Motorized Bicycle General Discussion' started by Henshooter, Feb 19, 2014.

  1. Henshooter

    Henshooter New Member

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    Hey guys I just replaced my spark plug with the NKG one and noticed after I had gapped and placed it and was running the motor a very small bubble was eminating from where you screw the plug into the head ,I've tightened the plug as much as I can without stripping the thread , is this common or is it an issue I should address and if so how ,with a bit of thread tape ?????

    Cheers guys Henshooter
     
  2. rustycase

    rustycase Gutter Rider

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    It's not uncommon...
    Try a copper crush washer from another name of plug...
    or just a small dab of never-seize on the threads... NGK does NOT advise using never-seize compounds... but they don't own a chinagirl!

    the prob could be shabby tolerance on the drill and tap, or just the milling on top of the head where the plug seats... you got a mill???

    if it's not real bad it will probably plug itself up! lol
    Good luck
    rc
     
  3. Theon

    Theon New Member

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    Don't know if thread tape is the go,
    The problem would be where the washer meets the head.
    Can you get hold of a tap washer seating tool?
     
  4. Henshooter

    Henshooter New Member

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    Unfortunately no mill , I'm glad it's no great issue was worried it would decrease power or similar ,it's amazing the difference a good quality plug does make compared to the kit original ,was going to try the iridium ones but at $42 for a single plug stuff that .
    Thanks for the quick reply Rusty ,much appreciated mate

    Regards Henshooter
     
  5. Henshooter

    Henshooter New Member

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    Hmm yes I can , you reckon milling the surface with a washer setter would do it ,know exactly what your talking about ,I'll give that a go

    THANKS AGAIN LIFESAVER THEON
     
  6. rustycase

    rustycase Gutter Rider

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    OMG!

    pls don't drop $42 on a plug for a chinagirl !!!!
    lol

    yes, of course a leaky plug seal will lose a bit of power.
    it should be fixed, but NOT worth spending any money on...
    She's a cheap date... don't spoil her with dinner at the Ritz!
    rc
     
  7. Henshooter

    Henshooter New Member

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    No way in **** I'd spend that on a plug, I'd rather get a performance CDI unit for that price ,I'll give the washer setter a go and see how it turns out
     
  8. Donavan321

    Donavan321 New Member

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    You could also try a different plug, sounds like it's not tightening down firmly and there's a hairline gap which is where the oil bubble is coming from!
     
  9. Henshooter

    Henshooter New Member

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    Ok so I milled the surface with a tap washer setter and it worked well there was a small area that was raised roughly 1/3rd of a mm, a few quick turns and she's as flat as a pancake and no leak any more except.........

    I got a good plug and gapped it to .030 as recommended by a forum member here and the bike runs quite badly it has nothing at the higher end and misses somewhat , I replace the original kit plug into the motor and it runs beautifully ,go figure ???

    Not sure why but until I get a better CDI unit ( lightening CDI ) from screaming roo here in au I'll stick with the stock plug for now

    Regardless she is running well and has no leaks and I just fitted the front light ,not the best but will do the job until I get a good Cree light from eBay
    Now it just waiting for the rear lamp to arrive and she is well and truly finished

    I must say thanks for the enginuity Theon , I would have never envisioned using a tap washer setter , I had a small cap from one of my kids pop top drink bottles that fitted perfectly into the head to prevent any metal flake going into the motor and together they worked a treat so a big hoorah to you my friend

    Regards Henshooter
     
    #9 Henshooter, Feb 23, 2014
    Last edited: Feb 23, 2014
  10. 2door

    2door Moderator
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    I had a cylinder head with a crack in the plug threads. You couldn't see it until it turned black with oil/exhaust residue. It was a new head too and the symptoms were oil seeping from the plug threads. I never saw bubbles but I'd check the head very closely if I were you. Compression loss would be minimal but it does make for an ugly engine.

    Tom
     
  11. xseler

    xseler Well-Known Member

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    My engine didn't like a wide gap like that.........I found that .024 to .025 worked best for me (original CDI).

    Best of luck!
     
  12. Theon

    Theon New Member

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    I was meaning to ask how you went with that,
    Excellent, I was taught to gap a plug to 20 thou.
    A hacksaw blade, or my thumb nail seems to be about right.
    A little more gap is good if you have a high power ignition, but for general Lawn Machinery,
    Which these motors really are, 20 thou works for me.
    And gets me 8500 Rpm with out any trouble.
    My 9500 RPM motor runs a 500 Ohm Mag and standard CDI (as yet), No problems.
    In a straight fire head I run either the B7HS and remove a couple of threads (photo1), or a Z4JC 3 prong Plug and remove a couple more threads from the head (2). The standard Z4C that comes with your EBay Kits sits way to deep into the plug recess, and I do not use them for anything (3).
    With an Angle fire Head I use a BP7HS and again remove a couple of threads (4).
    [​IMG][​IMG][​IMG][​IMG]
     

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  13. Henshooter

    Henshooter New Member

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    The recommended plug was a NGK B6HS and maybe the gaping is the problem , I'll try regapping to .020 and see how she goes , when you mean removing thread do you mill the thread on the head or the plug ,and how do I go about milling it Theon

    Thanks again for the help guys ,greatly appreciated
    Regards Henshooter
     
  14. Theon

    Theon New Member

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    Sean I'm going to send you an old head as well.
    I mean with a Dremel, like in the photos, remove any excess thread so that there are no hot spots in the combustion chamber.
    Who recommended a 6?
    I'd stick to a 7.
     
    #14 Theon, Feb 24, 2014
    Last edited: Feb 24, 2014

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