Optimus 111 tank - a simple job that turned into a nightmare

Discussion in 'Fettling Forum' started by Twoberth, Jun 24, 2019.

  1. Twoberth

    Twoberth United Kingdom Subscriber

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    I decided to clean an old Optimus 111 that I have had for a while, and I know it works well.
    A simple job that turned into a nightmare.

    On trying to remove the tank from the case one of the bolts unscrewed from the tank easily, but the other just spun around. At first I thought the thread was stripped, but it turned out that the bolt was stuck in the female threaded insert, and both were spinning round but still in position in the side of the tank. No amount of penetrating oil and patience would solve this one so I had to cut the bolt off to remove the tank.

    DSC08140.JPG
    I have never examined one of these female inserts before, but it is a double insert and the inner threaded one was loose in the outer case. If I brought a strong magnet close in, the inner would move about 1mm out of the outer case, but I couldn't remove it or get the bolt stub out.

    DSC08144.JPG DSC08146.JPG

    No problem!
    I will solder the lips of the inner and outer cases together, drill a hollow near the edge of the bolt stub and then tap anticlockwise with a punch to remove the bolt stub.

    DSC08149.JPG

    Then, while tapping, disaster struck and the whole insert assembly fell into the tank.

    DSC08150.JPG

    Thankfully the steel bolt stub was still in the insert, so it was easily removed through the filler hole using a telescopic magnet.

    DSC08151.JPG

    I decided to replace the insert with a blank nut fitted from the inside of the tank.

    First I had to solder a steel plate on one side of the nut and trim it so it would fit through the tank filler hole.

    DSC08165.JPG DSC08168.JPG DSC08172.JPG

    Then I had to roughen the inside of the repair hole using a Dremmel grinding wheel and then degrease the inside with a pipe cleaner and meths.

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    Before I removed the Dremmel bit with the telescopic magnet, I tied a piece of string on it so that I had string going inside the tank from the repair hole and out through the filler hole to help locate the repair nut on the inside.

    DSC08189.JPG

    I didn't want to risk using solder again in case I melted the blank plate joint, so after threading a stud onto the repair nut and tying the string to the stud, I cleaned and pre-loaded the nut surface with JB weld, and then pulled it into position through the repair hole.

    DSC08190.JPG

    Then I suspended the whole tank from the string and filled around the outside of the hole with more JB weld.

    DSC08191.JPG

    After a 24 hour cure in the airing cupboard the JB weld was cut back and the stud removed.

    DSC08201.JPG DSC08198.JPG DSC08200.JPG

    The tank leak tested well under pressure, but I feel I can make the repair stronger. Instead of using solder and JB weld, I could braze the blank plate onto the nut and then solder it into position.

    Has anyone else had any experience with this sort of repair? I looked through the threads, but I may have missed some relevant ones.
     
  2. Tony Press

    Tony Press Australia Subscriber

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  3. Twoberth

    Twoberth United Kingdom Subscriber

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    @Tony Press
    I had forgotten is fettle of yours. Lots to be learned from it, so thanks for the link.
     
  4. Simes

    Simes Subscriber

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    Every day a learning day here. I have to admit the sleeved insert I wasn't aware of until your very unfortunate experience. Something to hopefully retain in whats left of the memory if I have to do something similar.
     
  5. igh371

    igh371 Subscriber SotM Winner

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    I would never have thought to find that sort of threaded insert on one of our stoves, but the assembly looks rather familiar from the automotive and aerospace worlds. Known as 'Rivnuts' that type of insert were used, for example, to enable threaded mounts to be fitted into box-section Land Rover chassis for the attachment of bits of ancillary equipment. The 'Rivnut', aka Riv-nut, Nutsert or Rivet Nut, is still available and is a very secure and, with the right tool, easily fitted threaded insert. It is designed for situations where access is only possible from one side of an otherwise closed assembly:thumbup:
    Ian.
     
  6. Twoberth

    Twoberth United Kingdom Subscriber

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    @igh371
    Ian, many thanks for the detail on the 'Rivnuts'. I have never come across them before.
    Here are some more pictures of the offending item.

    Before bolt-end removal.
    DSC08155.JPG DSC08156.JPG DSC08159.JPG

    After bolt-end removal with bolt extractor drill bit (thread is now knackered).

    DSC08202.JPG DSC08203.JPG

    The inset is quite heavy for its size (6 gms), being two pieces of fairly thick brass pressed/soldered together.
     
    Last edited: Jun 25, 2019
  7. igh371

    igh371 Subscriber SotM Winner

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    Hi Duncan,
    Hopefully you've already sorted out this tank. But if you ever have to do it again you'll easily find Rivnuts online or at your local engineering tools supplier, and in a grand variety of different thread sizes. The simplest old-type only require deft use of 2 spanners to fit, more modern versions use an applicator very similar in principle to a pop-rivet gun.
    Ian:thumbup:


    @Twoberth
     
  8. Twoberth

    Twoberth United Kingdom Subscriber

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    For information, a good fit replacement bolt for the Optimus 111 tank-to-case fitting is a 1/4 inch UNC.
    DSC08205.JPG
     
  9. Twoberth

    Twoberth United Kingdom Subscriber

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    Stove now running as normal, with no leaks from the new joint.

    DSC08207.JPG DSC08208.JPG DSC08211.JPG

    I ran it at full bore for about 10 minutes without the heat shield and the tank got nice and hot. So that will give a nice final cure on the JB weld.

    Finally, after a two day distraction, I can now start to clean it as originally planned!
     
  10. theyellowdog

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    In my experience these fittings are soft soldered in place (but some may be braised / hard soldered, I think). I have no experience with jb weld, but I have soldered these inserts back into an optimus 22 tank. It was of one of those jobs where I was not confindent in the results, but it worked fine. Well done on your repair.
     
  11. Twoberth

    Twoberth United Kingdom Subscriber

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    While on holiday I was mulling over the above comment by @theyellowdog. While I was happy that the JB weld would be strong enough in compression (under the tank pressure) I had a nagging feeling it wasn't going to be strong enough in tension (if the hanging bolt was inadvertently screwed too far into the JB welded nut assembly). So I decided to do a destructive test when I got back home, and sure enough the JB weld failed as soon as the hanging bolt was screwed up tight against the nut backing plate.


    So, rather than soft solder the backing plate onto the nut and JB weld the assembly in position, I decided to silver braze the backing plate onto the nut, and then solder the assembly in place. First I repeated the destructive test with both a brazed and a soldered joint,
    DSC08244.JPG DSC08250.JPG

    and the results were much better, with the cap bowing out before the joints broke as the bolt was screwed in.

    So, with a newly brazed nut/ backing plate assembly pre-soldered and fluxed,

    DSC08249.JPG

    It was hung in position and more solder and flux added as it was heated

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    The hanging stud had been coated in nail varnish so that the solder didn't run down the threads, and then when cool the stud was unscrewed and the joint leak tested under pressure. It now has one slotted domed hanging bolt and one hex headed bolt to remind me of the repair.

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    It's back in its case now, and working as it should.
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    And back on the shelf with the other 111s. Not nearly as many as @Doc Mark !
     
  12. snwcmpr

    snwcmpr Subscriber

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    I did a similar repair of a Campingo. I did solder the area.
     
  13. Doc Mark

    Doc Mark Subscriber

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    @Twoberth ,

    MAN, that an adventure you endured with that 111T of yours!!! Thankfully, I've never experienced something similar with my own 111 family of stoves. I do not possess, or have not learned, the skills that you have mastered, and thus would be up the proverbial creek, without a paddle, for sure!! Well done!!! Thanks for linking me into this thread, as I'd missed it when it first posted. Again, well done!! Take care, and God Bless!

    Every Good Wish,
    Doc
     
  14. Tony Press

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    Good job.

    Cheers

    Tony