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  • Help requested for cast iron engine block repair

    Hello all,

    I have a welding service in Phoenix and regularly am called out to repair aluminum trannies and engine blocks. To date I have had no problem repairing these as they are pretty straight forward. However, this last call yesterday was everything but.

    I was called out to repair some broken motor mounting points on what turned out to be a cast iron block. I was not prepared for this repair as I only carry about a half a dozen ni-rods and this one would have taken at least a dozen and maybe two dozen. This was basically a build up job of filling in the broken threaded holes (there were two broken mounting holes) and putting enough material down to drill a fresh hole and tap it.

    I made the decision to with brazing rod and flux as the fact that I was brazing on the outside of the block (where it meets the tranny) meant that expansion would go outwards without running into obstructions (like gussets, etc.) that may build up stresses when it expanded and cooled. In short, the metal was free to expand as much as it wanted in any direction and shrink again without running into stress points.

    I tinned the surface and brazed away, building up both mounting lugs with enough material for the next step. The bronze bonded great in textbook fashion. Keep in mind that I have never attempted this type of repair in this fashion before.

    Once cooled, I marked off the excess material to be cut off using the engine mount as my template. I marked the holes in this fashion with a sharpie, center punched them and drilled out the holes. So far so good, everything was going beyond my wildest dreams.

    Now the *****!! When I attempted to cut threads into the holes I found that the brass was too brittle and I was unable to continue with the plan. Every time the tap cut into the brass and grabbed, the next twist broke the beginning threads and the tap stopped cutting. After a few efforts, it was evident I needed to stop and assess where I was at. Unless there is something that will make cutting the threads possible, I think I have to abandon the "cutting threads" route. I am hand cutting the threads with tap and hand "T" chuck.

    What are my options? I have thought of only two.

    1.) To drill out the hole and sink a stud in it to be held with an industrial epoxy like JB weld. I picked some stuff up at the local welding supply that's called "Lab Metal" which is sold not as an adhesive, but as a filler material. Among its list describing uses is "repair of over-bored holes". This is exactly what I had in mind. Over-boring the hole, sinking the stud in it and filling it with this stuff that would grab the threads and fill into recesses that I would cut into the hole with a high speed burr.

    2.) See if a silver solder could be employed to solder the stud into the hole. I could over-bore the hole slightly larger than the stud, enough to be a slip fit, heat the area and let the solder get sucked into the hole via capillary action, forming a tight bond and mechanically sound (hopefully) joint that would stand up to the abuse engine mounts take on a daily basis.

    Anyone have any thoughts on this one? My first choice would be to try and cut the threads, but am not sure how to go about it given my experience so far. This if for a four cylinder Nissan sedan, not a Ford V-10 engine. Maybe it may make a difference in terms of stress the part will take.

    Any and all ideas will be considered seriously.

    Thanks in advance,

    Tony

  • #2
    Hey Tony,
    Your repair sounds like it came out ok & it shouldn't be that difficult to tap brass. I would strongly suggest to insure your taps are sharp & not dulling from use. If so, just get new ones.... a standard starting tap with tapered nose, & a blind-hole/bottoming tap with full threads to the nose. A really good cutting fluid is a necessity. I use DoDrill fluid with the best results & also use Tap-Magic for brass which works well for tiny holes. Tapping may take time with only being able to get 1/4 turns at a time & backing out & starting again. Brass cuts fairly easy with a sharp tap & cutting fluid. I'm sure others will offer suggestions.

    Denny
    Complete weld/mach./fab shop
    Mobile unit

    "A man's word is his honor...without honor, there is nothing."

    "Words are like bullets.... once they leave your muzzle, you cannot get them back."

    "I have no hesitation to kill nor reservation to die for the American Flag & the US Constitution."

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    • #3
      Got to be a bad tap, or need a better choice of tapping agent.
      OR BOTH.

      Even in aluminum-bronze (Ampco) you should be able to tap it.
      Anything other than a perfectly sharp tap, well centered will be a problem.

      Watery tapping fluids are not as effective as the waxy and pastey ones.
      vg
      sigpicViceGrip
      Negative people have a problem for every solution

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      • #4
        Pictures would be nice.

        I've machined and tapped bronze and it is very brittle. It seems you have to stay with it even if the threads start to break at the beginning. Once you establish a straight tap where the tap feels like its not moving side to side it will tap . Slow and good pressure on the tap while trying to hold it straight should get it to tap. Also a brand new tap would help and some tap magic. Dont buy a cheap tap.

        If the thread holes get dammaged during tapping can you prep, refill and try again?
        sigpic
        Miller trailblazer 301G
        Miller S22P12 feeder w/ss case
        K&K 300 amp 15' .035-.045 (Bernard)
        Miller HF-251D-1, Weldcraft AC torch pkg
        Hobart HH187
        Harris DLX STLWKR
        O/A & chemolene
        WARNING These stunts are performed either by professionals or under the supervision of professionals. I insist no one attempt, recreate, or re-enact any activities performed.

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        • #5
          Engine block project solved!!!!!

          Hello all,

          thanks for all your input and ideas. I returned to the job and attempted the thread cutting operation again, this time with a new tapered tap. This made all the difference as the tap I used yesterday had only a slight taper more like a thread chasing tap.

          Once it went in for a few twists, it grabbed, self centered (almost) and dug right in cutting like butter. I sprayed liberally with "Sprayon" cutting fluid no. S00208. This was the only stuff I could find on the fly after visiting three hardware stores that only carried pipe cutting fluid. It worked like a charm though and included bronze, brass, aluminum and ferrous metals in its description on the label.

          My plan "B" was to camber the hole with a countersinking bit and use that groove to weld a stud in place so that the finish was more or less flush with the engine block. Luckily it didn't come to that.

          It was suggested on another forum (www.smokstak.com) that I use 7018 for this type of repair in short stringer beads with peening inter-pass until cool and then proceed again with another 1/2 rod of stringer bead.

          This will allow for an all ferrous repair including material properties and color matching (which is critical to restorers). This forum is dedicated to people who restore antique tractors and related machinery. They deal with old cast iron all the time and I will practice that type of repair as see how it works.

          Attached are pictures. Thanks again for all the help and encouragement. I hope to return the favor when called upon.

          Thanks,

          Tony

          Comment


          • #6
            Final thoughts on engine block repair

            Hello once again,

            I thought it would be good to mention that on the www.smokestak.com forum one member gave me a good idea that I think is important to pass around. He suggested to me that if the hole were within 3/8" there is a special repair drill/tap/bolt product that will do just that. He said it can drill the hole, tap it and is a bolt with threads on the upper part.

            It is applied with an impact wrench. While it was too late for this project, I think I will get a few to keep on my truck for just such situation. He said they are a common repair part/tool carried by lawn mower repair shops.

            Another member of the AWS forum said that he has personally destructive tested silver brazing rod welds and that the base metal broke before the silver soldered joint did. He suggested to use that approach as a plan "B" should tapping fail. If I had silver solder in hand I would've gone that route. That is, drill out the hole so a stud would just slip fit into it, then heat the joint and let the sliver solder get sucked into the hole, bonding the stud in the process. Luckily the tap worked and these are lessons that have been archived in my brain for the next time I cross this bridge.

            Thanks again to all,


            Tony

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            • #7
              Originally posted by therrera View Post
              I thought it would be good to mention that on the www.smokestak.com forum one member gave me a good idea that I think is important to pass around. He suggested to me that if the hole were within 3/8" there is a special repair drill/tap/bolt product that will do just that. He said it can drill the hole, tap it and is a bolt with threads on the upper part.


              It is applied with an impact wrench. While it was too late for this project, I think I will get a few to keep on my truck for just such situation. He said they are a common repair part/tool carried by lawn mower repair shops
              huh... thats all I have to say about that
              sigpic
              Miller trailblazer 301G
              Miller S22P12 feeder w/ss case
              K&K 300 amp 15' .035-.045 (Bernard)
              Miller HF-251D-1, Weldcraft AC torch pkg
              Hobart HH187
              Harris DLX STLWKR
              O/A & chemolene
              WARNING These stunts are performed either by professionals or under the supervision of professionals. I insist no one attempt, recreate, or re-enact any activities performed.

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              • #8
                Well, all I can say is that gentleman was correct, Silver Brazing Alloy is really awesome stuff.

                Let us know how the job turns out.
                Lincoln Idealarc 250
                Lincoln Weldanpower CC/CV engine drive
                Lincoln LN-25 wire feeder
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