Rebuild plastic stripped thread?

  1. Gragson

    Gragson Forum Supporter

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    413
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    Bucks
    Stripped & rebuilt a carb on a poorly running cb250, it has a choke valve/plunger that is secured by this plastic nut that screws into the aluminum carb body, its strpped and will not nip up. The part appears to be NLA from Honda and the thieves known as CMSNL want over £60 delivered as it comes with a spring and the wee 50p valve. Tried a bit of PTFE but its still not nipping up enough to my liking.

    I was thinking of smearing a tiny bit of JB weld on the thread and turning back in then out to let it dry hoping it would make a better thread (not a great bodge..), there is only about 3mm of thread to start with.

    Any better ideas folks?

    IMG_0262.jpg
     
  2. eLuSiVeMiTe

    eLuSiVeMiTe Forum Supporter

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    8,882
    Location:
    Bedfordshire England
    Is there a release agent for jb weld.
    Squirt of wd40 in the hole. Smear the fitting in jb and screw in for eg. No idea if wd works.

    Would a different product be better for the plastic
     
  3. Ruffian Member

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    1,711
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    Devon UK
    Get it machined in alloy??
     
  4. Gragson

    Gragson Forum Supporter

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    413
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    Bucks
    The boy could do that, but I would like it sorted before I expire :whistle:
     
  5. Ruffian Member

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    1,711
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    Devon UK
    I recon someone could machine those easy enough if you know someone capable with a lathe on some alloy hex bar.
    Probably not as bad a time scale as you recon.

    I know a decent Exeter baised boy who could do it easy enough.
     
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  6. Ali

    Ali Member

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    357
    Location:
    Cheshire
    Find something with the same thread, use it to sleeve over the old one, a bit of lathe work for someone? Just glue in place? Quicker than making from scratch anyway.
     
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  7. 8ob

    8ob Forum Supporter

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    4,403
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    It looks m10 ish, possibly cut an m8 onto the existing knobed thread and twiddle/glue a helicoil onto it. I think m8 is an m10 on the outside, may be worth looking into as they are pennies.

    Bob.
     
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  8. addjunkie

    addjunkie Member

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    5,239
    Location:
    Northumberland. Reet oot in the sticks
    Put a bit of jb weld or similar on the damaged part of the thread, then dress with a thread file.
     
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  9. outofthefire

    outofthefire Member

    Messages:
    2,048
    Leeds
    If it is a thread you've got a tap and die for, cut it off flush, drill and tap it and make a replacement piece out of ally that will screw into both pieces
     
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  10. pedrobedro

    pedrobedro Man at Matalan

    Messages:
    9,842
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    Drill down through a short bolt and JB a connection into it.
     
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  11. Pigeon_Droppings2 Member

    Messages:
    1,956
    Location:
    london
    Test with a bit of acetone on a cotton bud....if it dissolves then you might be able to soak the thread and screw it into a nut and let it dry.

    ....but not all plastics dissolve in acetone so might not work!
     
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  12. Pete.

    Pete. Member

    Messages:
    8,345
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    Kent, UK
    What thread is it? I'd be tempted to turn it down and use a helicoil on it, externally. Or you could probably make one from delrin.
     
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  13. R-D-R Member

    Messages:
    949
    Location:
    Derbyshire - England
    Is it a weird thread? Looking at the ruler it’s M10 ish, grab an m10 bolt and cut it down?
     
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  14. zx9

    zx9 Member

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    3,448
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    Be careful if you do this, Japanese bikes have a lot of metric fine threads.
    I am not saying it is, just something to watch out for.
     
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  15. Pigeon_Droppings2 Member

    Messages:
    1,956
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    london
    Most Jap cars I work on are a variety of metric threads...the thread pitch does vary depending on the size too so you do need to be a little careful to identify the thread.

    Having said that they stick to standard stuff when it comes to hydraulics it seems....which makes it even easier to get caught out of course!
     
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  16. mtt.tr

    mtt.tr Member

    Messages:
    1,101
    Essex England
    Is it a mikuni i might somewhere have one
     
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  17. wyn

    wyn Member

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    2,975
    Location:
    Cardiff
    Will the plastic "nut" also have an integral detent arrangement to hold the choke in the up position?
     
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  18. Gragson

    Gragson Forum Supporter

    Messages:
    413
    Location:
    Bucks
    Sorry poor reference pic, it is bigger than M10 was M12? or M11 even???
    The pitch is a bit hard as its pretty "cattle trucked", on a gauge closest looks like 1.0, getting that wrong in plastic and the carb thread will win, if I get it wrong with ally or steel....
    Its a Keihin carb and the top of the nut hole reduces to hold the cable ferrule end.

    Really appreciate all these replies, gives me some much better ideas :thumbup:

    IMG_0263.jpg IMG_0264.jpg
     
    eLuSiVeMiTe likes this.
  19. Pigeon_Droppings2 Member

    Messages:
    1,956
    Location:
    london
    I had a similar thread issue with the turbo oil feed on the Nissan Figaro.....it turned out to be something totally odd and took me weeks to find a matching fitting.

    I think if you take a picture of the thread while holding a ruler along the centre axis (if that makes sense)....then if you zoom in you should be able to work it out....need a descent metal ruler though as the difference between 1.0/1.5 ain't huge.

    In my case I had a good length of threads so I could measure across half a dozen....you'll have to be quite precise I think.
     
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  20. cheb Forum Supporter

    Messages:
    422
    Location:
    Outer Hebrides
    Hold a bolt of known thread size against it and hold up to the light The diameter of the bolt doesn't matter, if it's the correct size you'll know.

    Standard metric are M6 x 1mm, M8 x 1,25mm, M10 x 1.5mm and M12 x 1.75mm.
     
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