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Ever cross-threaded a spark plug?  Trust us, it sucks.  You generally have to heli-coil ’em since you can’t re-tap it because you risk dropping bits of metal into the engine — until now.  These expandable spark plug socket rethreaders from MAC Tools slip past the damaged threads then expand to engage them, allowing you to “chase” the threads from the bottom up.  Debris comes up and out with the rethreader.

This is most definitely a specialty tool, but like all specialty tools, when you need it, you need it bad.  This could really pull your acorns out of the fire if you (or one of your techs) is a little overzealous installing plugs.

MAC sells ’em in a three-piece set that fits common sizes — 10 mm, 12 mm, and 14mm — for $90.  They also sell the less-common 18 mm version separately.  You can pick ’em up online or (of course) via your friendly neighborhood tool truck.

3-Pack Expandable Spark Plug Socket Rethreaders [MAC Tools]


10 Responses to Re-Tap Spark Plug Threads Safely

  1. Jake says:

    I am blessed enough to never have done this. I am confused though because I thought you needed to tap for helicoils. Could someone explain?

  2. Jon says:

    Is there also a permanent magnet in the bottom that will grab any stray shavings?

  3. Old Donn says:

    Aside to Jake. This tool chases existing threads, assuming they’re not too damaged and the plug will thread back in afterwards. You’re right, if they’re too far gone the hole will have to be tapped and heli-coils installed.
    This tool is inserted in the hole past the threads, expanded, and twisted out. Ergo, any shavings should be pushed out with the tool. A magnet shouldn’t be needed.

  4. SouseMouse says:

    Besides, a magnet won’t do squat if you have aluminum heads.

  5. ambush27 says:

    I don’t think I could justify spending money on a tool like that, I’d end up just removing the head and re-tapping it. Its still a cool tool though.

  6. Stephen68 says:

    I have a Kawasaki 300 bayu 4×4 and this tool work great. It was in the shop for repairs and when i got it back i found the sparkplug cross threaded. This tool along with a little greese to catch any shavings saved me tons of money. lets just say that that shop lost my bisness.

  7. CJ says:

    Friendly neighborhood Mac Tool truck? Haven’t seen one in years. Yet, I did find these at AutoZone for about $30 bucks.

  8. Paul Johnson says:

    I have a 2001 PT cruiser with the 2.4 liter 4-banger. #1 spark plug threads are toast. The plug wil thread in part way, but will not seat and I’m getting serious blow-by. Will this tool do what needs to be done? Can a retard like me do this job, or should I take it to a machine shop? I don’t wanna pull the head, ‘cuz that would suck.


    • Oscar says:

      This tool works from the inside outward. insert the tool with plenty of grease to catch the shavings pull the rod to expand the tap and start the tap in reverse as if you were removing the plug. This is a great tool if you know how to use it.

  9. James says:

    would I have enough of room to use the tool on the firewall side of the motor on a 2004 Dodge Stratus 2.7L v6…very tight quarters

    someone email me if you have had this problem on model car and motor size.

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