Spark plug thread size

Discussion in 'Engine, Fuel and Exhaust' started by 2006FXDCI, Apr 30, 2010.

  1. 2006FXDCI

    2006FXDCI Active Member

    182
    28
    1
    My friend has an 2003 Road King and his spark plug threads are a little messed up he wants to run a tap in it to clean up the threads does anyone know what size and thread pitch they are?
     
  2. Breeze3at

    Breeze3at Well-Known Member

    4,644
    83
    124
    I believe they are 12 x 1.25 mm. Be careful not to get shavings into the cyl.
    grease on the flutes of tap will catch a lot of it.
    Threads "a little messed up" is like "a little pregnant". Getting the tap past the first couple of threads and then following the good ones is difficult at best. If the plug doesn't seat solidly or threads fit poorly, heat transfer will suffer. Good luck.
     
  3. jaxdwg

    jaxdwg Active Member

    209
    28
    3
    I'd pull the pipe and make sure the exhaust valve on that cylinder is open. Then I'd stick and air hose in the exhaust port and blow heck out of it while chasing the thread. And, it may be a 14mm x125 thread so check the new plug in a die to be sure before proceeding, to make sure all is good ahead of time :s
     
  4. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

    5,276
    133
    156
    Usually when the threads are as you say a little messed up they are actually biffed and running a tap through them wont do anything to fix them unless material has been added to them as in paint or powder coat
    in this case i would take the head off and do a proper fix by some sort of thread insert

    Brian
     
  5. 2006FXDCI

    2006FXDCI Active Member

    182
    28
    1
    Thanks for the info everyone, I will let my friend know the size so he can get a tap or thread chaser.
     
  6. glider

    glider Veteran Member

    25,464
    108
    44
    Most auto stores that carry some tools carry a thread chaser for spark plugs. It's a double ended chaser for different sizes.
     
  7. Jack Klarich

    Jack Klarich Expert Member

    18,544
    153
    399
    When cleaning threads, i a few turns , out repeat if tap binds do not force it and grease will help trap the shavings, if you are stuck and cant find a tap take an old spark plug and file flutes into the threads this will work like a tap when in a bind:)
     
  8. glider

    glider Veteran Member

    25,464
    108
    44
    This is all that is needed in the proper thread pitch, available in most auto parts stores.


    [​IMG]
     
  9. jaxdwg

    jaxdwg Active Member

    209
    28
    3
    Glider; would someone use the big end or the small end?---just kidding---jack :s
     
  10. glider

    glider Veteran Member

    25,464
    108
    44
    You'd have to look that up in the manual Jack. :newsmile040: