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Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

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  • Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

    Rebuilding '78 Johnson, 150 hp, cylinder head bolt hole is stripped. I've read through several threads most recommend a Helicoil. What I don't understand is if I have to retap for Helicoil why not just retap for a larger bolt and thread? I'd rather trust a machine shop to do it but I have it almost completely reassembled and it would be tough to transport it.

  • #2
    Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

    I had a similar problem with a Honda bike head. Drilled and tapped for a bigger (stronger) bolt. Worked very well.
    sigpic

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    • #3
      Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

      You may not have enough meat to drill for a larger bolt. The bolt you stripped the threads on is a 5/16. You would have to go to 3/8 and depending on which hole it is, you chance cracking into a cooling gallery. Heli coil is the easiest Method.

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      • #4
        Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

        Do whatever you want, but I wouldn't even consider the larger bolt. Heli Coil it.

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        • #5
          Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

          Whether you heli-coil it, or not, you will be cutting the hole out bigger. I would follow F_R's advice though and heli-coil it, because you will have steel threads to bolt into, versus aluminum.
          Admiral Zephyr

          1941 Johnson HD-20 (in restoration)
          1947 Sea King 5hp
          1948 Evinrude Sportsman
          1951 Evinrude Fastwin
          1955 Johnson CD-12
          1955 Johnson RD-17
          1955 Evinrude Big Twin
          1956 Johnson RD-18
          1957 Evinrude Big Twin
          1958 Evinrude Fisherman
          1958 Johnson FDE-12
          1959 Johnson RDSL-21B
          1974 Tanaka 1hp (screamin' drink mixer )

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          • #6
            Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

            A heli-coil is actually stronger than the orginal threads. Go with that.

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            • #7
              Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

              Agree. Helicoil. Then you get to use the same size bolt (body diameter) so there should be no interference issues.
              sigpicMarada 2100 Executive Series, 5 Litre V8 with Mercruiser Alpha 1 outdrive. 2007 K-Z Spree 260 RBH, all = a whole lot of family fun !!!!

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              • #8
                Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

                Use a keensert as it the strongest and will handle full torque...
                When in doubt,Trim it out!!!
                Business Owner & Certifed Technician
                Boats I own & use
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                • #9
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                  Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

                  Thanks all! The threads in another hole looked bad also, today I put a Helicoil in both. It was easier than I thought. Installed gaskets, heads, and torqued to 20 ft lbs as specified in manual. Awesome! Thanks again.

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