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It can happen to the best of us: one moment of inattention results in a cross-threaded spark plug hole. You can either install a helicoil and hope for the best, or send it out to have the whole shebang re-tapped. Now you have another option. The Back-Tap can fix that cross-threaded hole from the inside — without pulling the head.

The Back-Tap is a tap with expandable threads and a mandrel to catch errant metal shards. Apply a dab of grease to the mandrel, then place the device in the hole past the damaged threads. As you back it out, the cutters expand out to engage the undamaged threads, then gently reshape the damaged ones. The greased mandrel keeps metal filings from ending up in the cylinder.

The result: a task that could potentially take days and cost hundreds of dollars is done in minutes for less than a hundred bucks.

MAC offers a three-piece kit that includes a 10mm, 12mm, and 14mm Back-Tap for $90. You can buy Individual taps from various sources for about $50 each.

Back-Tap [Official Page]
Back-Tap Kit [MacTools.com]
Street Price [Google Products]
Via Amazon [What’s this?]


6 Responses to Un-Oops That Cross Threaded Spark Plug Hole

  1. Patrick Starr says:

    Actually, the best deal on this tool can be found in the PowerBuilt Tool line by Alltrade.


  2. Bart's Dad says:

    These taps are not usually used for a cross threaded plug, but from damage done when removing a seized plug in an aluminum head.

  3. William says:

    This is nothing new and made by KABA Tools of Taiwan for Mac. It’s also available though Mac’s new parent company, PROTO and several online tool stores. When the CEO of Mac left in April, PROTO took over the reins so much of what is now being made in the PROTO/Dallas plant and out of China and Taiwan, is all the same – just stamped different and prices higher for the truck guys.

    Now if I could just find a Mac distributor to replace all my broken tools, I’d be happy. All three distributors folded shop in my area in the last two months and Mac HQ is unwilling to help. According to them, PROTO/Stanley is looking to dissolve the company over the next three years.

  4. joaedmonds says:

    Hey guys,
    I am only looking for
    The best soft to PC-where to buy, join site & other tipe to do a home online business.
    With best regards.

  5. i am trying to locate a mac tool dealer in the cleburne texas area
    any information will be greatly appreciated
    thank you
    ernie mccuistian

  6. karl says:

    Had a new rebuilt head on my 90 Honda Civic. Spark plugs wouldnt completley bottom out. Not sure why? Bought this tool and put anti seize grease in the threads and used a deep socket. Didnt tighten all the way the first pass. Took it easy and backed it every couple turns like a tap. Solved the problem. Was worth it for me. You have to play with the adjustment a little to get it right. Better to check the threads before installing heads. Live and learn that machine shops dont always do what they should.

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