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Broken Head Bolt In My Flathead Ford

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  • Broken Head Bolt In My Flathead Ford

    EDIT: The variable speed has been bypassed. Just forward/off/reverse.

    The broken head bolt in the coolant passage. The welding trick didn't work this time, just broke off around .070" off the top of the bolt. Crooked and below deck I am just looking to bore out the bolt till I get a silhouette of the threads. Picked up a magnetic drill press to keep everything true. What type of self centering boring bit do you recomend for this exercise?
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    Last edited by Chris401; 07-29-2021, 08:41 PM.

  • #2
    Your best bet would be to put that head on a Mill and bore it from there........your not going to have much clamping force on that mag drill over cast iron that has water jackets.........Easily done on the mill, I would find the center of that bolt , center punch it and probably just use a 2 flute end mill that's just under the minor size of the bolt...


    • #3
      Absolutely the safest approach, but the problem is, it's a flat head. It's a head bolt, but it's broken off in the block. Gonna need a big mill.


      • #4
        Cut the top of the bolt flat and use a center drill to get you started straight.

        Let me ask, did you try to tig weld a nut to that bolt? I find with tig welding you can dwell a while and let it heat up a lot deeper than if you migged the nut on. Sometimes it takes a try or three for it to work.

        Tarry is right though, a Bridgeport or similar is your safest bet if you know someone. You might even try any machine shop and see how much they’ll charge you for the job. Outside of that, once you get it drilled and can get a bolt extractor in there, you’ll probably still need to pour the heat to it. An easy-out is my last choice for bolt extractors though, so try and find a rigid broken bolt removing kit, something like that. Your problem is definitely solvable.


        • #5
          Originally posted by Aeronca41 View Post
          Gonna need a big mill.
          Nahh I put cylinder blocks on my mill all the time Click image for larger version

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          • #6
            That is one beautiful setup you have there, Tarry. Very nice!


            • #7
              Welded it a couple of times. The second time broke it off below deck.

              This is on an 8N tractor. If the block wasn't between a dozer blade and a backhoe then taking it to a machine shop would be my best option. I am going to use the drill I have to bore it out.
              Last edited by Chris401; 07-30-2021, 07:22 AM.


              • #8
                An old 8N....very familiar with your woes there. That bolt has only been in there for 70 years man!

                I’ve never used an end mill in a mag drill, my guess is you can spin it fast enough for it be effective, but worth a shot I suppose. I’d probably pick a HSS end mill at that low of a speed. If you go easy with a center drill or a spot drill and get a good start on the bolt then you can be successful.

                I figure the worst case is you end up drilling the hole oversized and putting an insert in. Not ideal, but what other option is there at that point?

                There are some welding rods that are designed for welding to a bolt down inside a bolt hole. The flux is non-conductive and the rod is directional. I’ve had success with those in the past, but they’re expensive and you probably can’t just buy one or two. It seems like you may be over that stage though. If you want to give some a shot, I can mail you some. I sent some to another guy a while back.

                Keep us posted on your progress, lots of stuff here to learn from.

                Ya, Tarry, nice BP for sure!


                • #9
                  I would mig it out
                  I may straighten out a lock washer so it doesnt grab, that first, then a flat then a nut.


                  • #10
                    Sometimes you have to try more than once to weld them out. I guarantee I could get that out by welding a nut to it. I used to keep a bucket with all the broken bolts I got out for customers, until it just got too big and heavy. Try again, turn up the heat. You will not weld it to the block, because that is likely what you are worried about, so turn the machine up a fair bit. This is likely a 5-10 minute ordeal once you have done a few.


                    • #11
                      In my previous carrier I've gotten a quite few out over the years by welding a piece of steel or nut to it. I've learned something like this in a cooling jacket can be larger with corrosion where the bolt is exposed to the coolant. Forcing it though the threads has a potential to crack what your removing it from. This is the first time I can remember when it hasn't worked for me. Like my first post said it is broken below deck, nothing to weld to. Might as well accept the first two breaks and take your time on the third try. I am made some progress with the bit I bought today.
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                      • #12
                        Being a through hole will make it a little easier to clear the threads out of you end up drilling through it.

                        Helped a friend with an EGR delete on his Ford a few months ago, everything went fine until we broke both of the little 6mm bolts off the exhaust flange. All he had at his shop was a little mig machine, I must’ve tried 6 or 7 times to weld a nut to those studs and never budged them. We ended up drilling the bolts out and tapping the holes to 1/4-20 for holding blank plate on the old hole.

                        Little jobs like this can make you crazy.


                        • #13
                          They can be done in the hole. Click image for larger version

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                          • #14
                            I forgot to say Ryan that I don't have any wire feed yet. I use an old cracker box. Once I get this old tractor burning oil again I can build a decent slab in the shade to work on. Hope to get back on it this after noon.

                            Sberry, there is a handy tool called a tap extractor. I am sure we could all beat our chest over our triumphs in our field of expertise. I do good if I can get myself out of my own messes.


                            • #15
                              My Experience in many of these repairs is you only get one good chance at the extraction and that's usually the first attempt.........From there it's downhill and turning into garbage quickly.........If it warrants I'll stick in the mill.......If there's room and access, I like grinding a little nub or flat spot in the center of the bolt with a small HS burr.....then take a sharp center punch and make a nice indent / point and from there if your successful you can start with a sharp cobalt 1/8" drill and work your way larger as your staying 90 degrees to the block until just the threads and a small margin of the original bolt remains......the first hole needs to be straight..........there with a little heat and a pick it will usually curl itself out with no damage to the original thread. Chase it and your done!!