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Discussion Starter · #1 ·
I recently noticed that my 2005 Elise is missing the rear center bolt for the front undertray
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I bought a replacement bolt from the hardware store. When I started to install it I could tell that after a certain point it was just spinning...luckily I was able to back the bolt out.

I would like to repair / replace the threads in the frame if possible. I'm guessing this is some sort of nutsert / rivet nut which has loosened up. Has anyone ever repaired or replaced one of these undertray fixings before? I tried searching but couldn't find any relevant threads.
 

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Inokinetic offers these for the rear subframe. @shinoo may know whether or not they would work for that location as well.
 

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Not an issue with just one missing...https://www.lotustalk.com/threads/elige-b117b0237f-front-undertray.426058/
 

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The HF rivnut tools are SAE only. And they have two of them, or did anyway. Get the beefier looking one, although both will do fine with aluminum rivnuts. Even the beefier looking one has trouble with steel 1/4x20's. I finally broke down and bought a real nice set off of aliexpress, metric and SAE.

You can also put a SAE insert in, then drill it out and tap it to metric.
 

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Discussion Starter · #11 ·
I see three different tools on HFs website, including this “professional” one:

Maybe it’s a new model and better than the others? But yeah I definitely have mixed feelings about the quality of their tools.
 

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That professional one is basically identical to the one I bought off Aliexpress, except it has a nice blow mold case that mine doesn't. I would have bought it from HF if they had it when I ordered mine.
 

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Discussion Starter · #14 ·
Okay so I put the front undertray back on and realized that the loose rivet nut is rattling against it. So I at least want to remove the old one for now. Any advice? I have removed rivets before but never a rivnut. Is it just a question of drilling it out like a rivet? It spins freely in the hole already which might make it hard to drill.

When I look in from the end of the frame extrusion, I'm surprised that these nuts aren't visibly compressed...maybe that's why they fail easily.
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Or I suppose I could just secure it temporarily with tape or a dab of clear silicone to try and stop the rattle.
 

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Maybe using long bar or screwdriver tap it enough to deform so it won't spin while drilling. Dab of silicon would stop the rattling if you go that route.
 
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Discussion Starter · #17 ·
Thanks, that makes sense. I went to HF today and picked up their tool. I can confirm it includes an M6 mandrel and it seems to be of decent quality. But I ran into some potential issues with using it:

1) The back of the undertray fits into a lip on the chassis extrusion, and this is so close to the rivnut that the tool isn't going to be able to bear against it properly. Here's a picture of the M6 mandrel separated from the tool and partially threaded into the old rivnut to show the issue (the lip has orange all over it).
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2) When I thread in the mandrel by hand, I'm meeting resistance when it gets to the end of the threads of the rivnut. Is it possible these rivnuts aren't threaded all the way through? I don't want to force it and get it stuck and have to cut it out.

It seems like I could solve both issues by slipping an appropriate spacer over the mandrel before I thread it in...something narrow enough that it only bears on the rivnut flange and thick enough to prevent the mandrel bottoming out. But I'm unsure if that could go wrong somehow and am leaning towards my original plan of temporary silicone or removal.

Thanks for reading the long post if you got this far. Partly just wanted to document this for others, but would also welcome advice.
 

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The threads may be a bit boogered in the rivnut. You can get either a thread restore set (proper way) or a cheap tap set (HF) and GENTLY run start the tap into the rivnut, being VERY careful not to cross thread it when it is starting, then finish cleaning up the threads at the end. It is threaded all the way through. I have never seen a blind rivnut.

Yes, a small spacer, stack of washers, piece of bar stock with a hole in it, whatever fits on there will work fine.

Worst case, you get a drill bit, grab the back end, drill the face off until the the thing pops out the back and put a new one in.
 
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