Re-tap captive nut - a question for the fabricators

nick_the_fish

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OK, trying to fit the new rear bumper. There are 3 bolts that I can't get to start in the captive nuts inside the chassis. They line up fine to its not an alignment issue. The bolts were damaged when I took off the tow eyes - it took a bit of grunt to release them - see photo below, so my thinking is that the captive nuts that they were in were also damaged hence not being able to start the new bolts in there. Is there any way I can re-tap the captive nuts to create a new thread?

IMG_1835.JPG


TIA

N
 

chapel gate

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Get a new bolt, spray plenty of diesel/wd whatever in the captive nut, start the new bolt, once it starts to get tight remove and spray more diesel/wd whatever in there. Keep repeating, going a little further each time until the bolt will run through with ease.
It's probably just rust and crap in the thread.
Or just use a tap if you have one.
Put copper slip on your new bolts.
 
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Towpack

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I’d be inclined to try a thread chaser first as it’ll clean up the existing thread without removing any more metal as a tap will do. If all else fails, drilling out and retapping in the next size up is the last option. My only concern would be the captive nuts breaking off inside the chassis rail making the job much more difficult.
 
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nick_the_fish

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Thanks for your input guys. Much appreciated. They are M12 fine pitch so drilling and re-tapping is going to mean going up to M14!

The problem I am having is getting the bolt started. It sounds like a thread chaser is the first option - but am I going to be able to get that started or am I going to have the same problem? I was wondering if it is worth drilling out the first millimetre to try to get to a good bit of thread to get the bolt to bite, but not sure if i'll damage the thread as I drill?
 

steverjuk

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Id just use a m12 1.25 tap and run it through should be fine, as the threads shouldn't be in that bad of shape. It should run in the threads already there and cut out all the crap thats in them.
 
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AndycruiserguyLomas

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When I fitted the alli front bumper to the 80 auto I ran a taper tap through and used new bolts, I did the same when I fitted a tow bar to the V6 Collie before I sold it. The only Issue I had with that job was one of the captive nuts became un-captive so I fitted a new nut with a stalk welded to it and fed it down the chassis and wound the new bolt into it.
New bolts, for what they cost is the way to go.
 
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nick_the_fish

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Ok, spent the morning grinding off material from the chassis so now the bumper slips on and off without a sledgehammer. Also got one of the bolts sorted by going in from the top which cleared the thread.

so, only 2 bad bolts to go and we should be home free.

@Chris I like your idea. The 2 problem bolts are inside the chassis furthest in on each side (see photo marked up below). Do you think your idea will still work? What are your movements these days? When are you free?

N
IMG_1836 2.jpg
 

Chris

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Dead easy Nick. You make a small, thick plate that fits inside and drill it to match the spaces you need - say 65 mm or whatever they are. Then you weld on two nice new nuts. Shove it down the chassis ( I weld on a welding rod to move it about) You can stick a blob of sealant on the back to hold it in place or even grease so that it stays put whilst you're wiggling things about. I've done this several times. I even made one that fitted the 4 holes in the side of the chassis just above your arrow.
 

Jon Wildsmith

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On a 100 series those captive nuts are on an L shaped plate that goes up the side of the chassis and the way the plate is spot welded to the side of the chassis not the bottom means the plate can get twisted and end up at an angle that means you can't get the nuts started. iirc the plate is not hard to chisel off and start again with a new home made plate on a stick like Chris offered. I realise you have a 105 but it may be the same. I've also chiselled the equivalent individual nuts off on an 80 series they're not held on by much weld.
 
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nick_the_fish

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Thanks @Jon Wildsmith , me and chris moved the conversation over to text to sort out logistics. He has kindly offered to make me a bracket which should do the job. I'll give the nut a wack today so its off ready for the bracket. Can't remember seeing a 'L' shaped bracket down there but i'll have a look. There are 3 nuts in that are, 2 of which are still good so only need to replace the 3rd one.
 
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