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Spark plug thread size

2006FXDCI

2006FXDCI

Active Member
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?
 
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.
 
Breeze3at said:
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.
Click to expand...

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
 
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
 
Thanks for the info everyone, I will let my friend know the size so he can get a tap or thread chaser.
 
Most auto stores that carry some tools carry a thread chaser for spark plugs. It's a double ended chaser for different sizes.
 
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:)
 
This is all that is needed in the proper thread pitch, available in most auto parts stores.


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