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Number plate nuts

Discussion in 'Bodywork, Tyres, Wheels & Trim' started by White230CE, Jun 26, 2009.

  1. White230CE

    White230CE Senior Member

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    Hi,

    Took off the rear number plate of my 230CE because I saw rust peeping through from the panel underneath. It turned out that the 4 holes for the number plate screws had been bodged with rawl plugs.

    Luckily, the rust hadn't taken much hold yet, so I was able to sand, clean and repaint, so the 4 holes are now back to how they should be.

    Each hole is a hex shape, and the new nuts from Merc are like a mushroom, having a hex shaped stalk topped by a wider circular cap. The number-plate screws screw into the top of the mushroom.

    Obviously, you push the stalk into the hole until the bottom of the cap rests against the panel. However, what is used to keep the mushroom 'planted' in place? Do I glue it, if so with what? Without any fixing, once I screw the number plate in, it could just pull out with the mushrooms attached! Tried pulling on the mushrooms fixed to my donor car, and they won't budge, so would like to achieve the same on the cannibal.

    Thanks
     
  2. turbopete

    turbopete Senior Member

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    i believe they re what is known as "rivet nuts" they are pushed into the holes and then a tool similar to a rivet gun is attached via the threads and it basically keeps the threads good whilst splaying the shank a bit, similar to a pop rivet. i have seen these applied using a long bolt and tightening a nut up to squeeze the threaded insert but its better done with the correct tool
     
  3. OP
    White230CE

    White230CE Senior Member

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    Thanks Pete. I'll look into where or how I can get hold of the tool.
     
  4. television

    television Always remembered RIP

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    The only fix possible now will be to use nuts and bolts with spacers about 4mm long, the other fix is to use the MB type number plate holders that you cold screw straight on and the number plate just clips in
     

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  5. OP
    White230CE

    White230CE Senior Member

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    Welcome back Malcolm! :D

    I'm really confused now.

    I guess you're saying that the nuts I've just bought can't be retro-fitted? Is that because I can't get at the rear of the panel they fit into, to do whatever needs to be done?

    If I can't use those nuts, how exactly do I use nuts, bolts and 4mm spacers? I'm trying to visualise but can't get it.

    Many thanks

    Ray
     
  6. television

    television Always remembered RIP

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  7. OP
    White230CE

    White230CE Senior Member

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    Malcolm, you are not muddled up at all. You're spot on!

    The diagram shows exactly what I've been supplied with: Nos 128, 149 and 146. But if I fit them in the sequence shown in the diagram, the shape of 149 doesn't seem to match the top of 128 or the bottom of 149. If the number plate goes between 149 and 146, still can't see how that tightens 128 in its hole.

    Pic attached.

    Thanks
     

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  8. television

    television Always remembered RIP

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    I am guessing now,,could the 128 be inserted from the inside of the boot and 149 goes over the hexagon sleeve part of 128 once it been pushed through the hole
     
  9. turbopete

    turbopete Senior Member

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    thats where the rivet gun type thing comes in IIRC! i was on the frost website getting prices for por15 earlier. they had the tool required but i didnt check the price im afraid
     
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    White230CE

    White230CE Senior Member

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    It sounds like from what you both (Malcolm and Pete) are saying, that I need somehow to get at the panel from behind. Trouble is, there is an inner skin which I haven't yet worked out how to remove, and on a quick inspection, I thought it might be riveted rather than bolted/screwed. I'll study Malcolm's diagram again, but in the meantime, any removal advice would be appreciated.

    Thanks
     
  11. television

    television Always remembered RIP

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    Well there is no way that the replacement in your picture can be riveted, that is a solid casting
     
  12. wiltsandy

    wiltsandy Senior Member

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    They don't look like typical rivnuts to me but they could be MB's version I suppose.

    If you can't get hold of the proper tool you can quite often put them in by using an additional nut that is slightly larger than the bolt so that it doesn't catch the threads. The reason for the nut is to stop the bolt binding on the rivnut and trying to turn it in the hole. Place the rivnut in the hole and then put the bolt through the extra nut and into the rivnut. A longer bolt may be needed for this. Tighten the bolt and it should pull the rivnut up to pinch the sheet metal.

    HTH
     
  13. television

    television Always remembered RIP

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    That has to be worth a go and nothing lost, so pop it in the hole and do up the screw tight and see what happens
     
  14. wiltsandy

    wiltsandy Senior Member

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    I think you're right though Malc that they're not rivnuts. They don't look like anything I've come across in the aircraft industry and they're used heavily there!
     
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    White230CE

    White230CE Senior Member

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    Thanks guys. I'll experiment tomorrow.

    What's really puzzling is that 3 of the same nuts are in place on my donor car and they stay in place without any bolt, and there is no sign of the plastic No. 149 either. It clearly takes some force to remove them, because the 4th hole on my donor car is distorted outwards, as are two on my cannibal - as if someone had to yank hard.

    I'll take a closer look, and a pic tomorrow morning, and report back.
     
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    White230CE

    White230CE Senior Member

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    One for Bolide/Nick Froome?

    Nope, I'm completely stumped. No idea how the nuts are supposed to be installed and made to stay in place. :confused:

    Bolide/Nick, if you happen to read this, are you able to shed any light on this please? Many thanks
     
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    White230CE

    White230CE Senior Member

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    Upon further internet research, I think it could be a rivnut after all, as Turbopete suggested. The selection on www.rivetnut.co.uk includes some identical/similar hex designs with threads, which they indicate can be applied one-sided using one of the tools they sell. See especially their 'Setting a rivet nut' link. I will contact them for advice and see what comes of it.

    I also, in the interests of research, sacrificed one of those already securely installed in the donor car. I used some mole grips, and the nut head was very soft and squishy under pressure going from round to oval. I pulled it out as a dentist might pull a molar, distorting the panel hole in the process. The only thing holding it in was the hexagonal stalk, distended and bloated, and I guess it got that way from having a rivnut tool applied to it.
     
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    White230CE

    White230CE Senior Member

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    On further reflection, I wonder if the black plastic spacer (see picture) is supposed to do what the nut in your example is to do. Do you think that is possible, or would plastic be too soft?
     
  19. television

    television Always remembered RIP

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    We have had a lot of post over the years,,it was not kind of MB to use 3 different metals, as this sets up the galvanic process. very few ever get all of the screws out, I had to drill out 2 of mine and re tap
     
  20. OP
    White230CE

    White230CE Senior Member

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    So even if I find the correct way to put these in, are you saying it's better not to because of the risk of corrosion arising from the three different metals in the bolt, nut and panel?
     

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