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HELP!! 28hp cross threaded spark plug hole

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  • HELP!! 28hp cross threaded spark plug hole

    I used the wrong size compression tester fitting and cross threaded the top cylinder hole. Now the spark plug will go in halfway and then it stops. I’m too afraid to take the powerhead off and take it to a machine shop because most of the bolts are rusted and I don’t want to break them. Would a rethreader be my best option? Thanks in advance for any help.

  • #2
    Try a tap, and if that doesn't work you should be able to install a helicoil or timesert without removing the head.


    • #3
      Correct me if I’m wrong, but if i install a helicoil or timesert wouldn’t that make the hole too small for the spark plug?


      • #4
        No it will not !----These are well engineered thread repair methods.


        • #5
          Bar the motor over until the piston is at TDC. Try a spark plug thread tap first. Re-tap using compressed air to blow the chips out along the tap flutes. No lube. Tap dry and slow. 1/2 turn, and then back up to break the chip. Repeat. When the tap gets 4-6 full threads below the top of the head, switch to a bottoming tap, or grind the lead in threads off the end of the tap and run the tap in until it contacts the piston. Then blow it out thoroughly.

          If you can torque up the spark plug -18 ft lb, you're good. If not, you're into the helicoil repair. Buy the full kit with correct drill, tap and insert tool. You'll have more chips to deal with. Use the compressed air and avoid lube.
          '96 Larson 174 SEI BR. 4.3LX 4 bbl Weber s/n 0F786604. Alpha One Gen II s/n 0F709315


          • #6
            Will this work? Are they one size fits all? I don’t see a specific size


            • #7
              they are not one-size fits all.

              there is a whole chart of sizes per SAE J548d
              Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

              1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

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              • #8
                Originally posted by Mthirsch14 View Post
                Will this work? Are they one size fits all? I don’t see a specific size
                Spark plug threads are 14mm.
                Our Questions Require Answers... If You Refuse To Answer Our Questions... How Can We Answer Yours?


                • #9
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                  Hurry run to a machine shop for proper help.----This may save you a lot of grief in my opinion.