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Stuck bolt in chassis of Triumph spitfire 1500

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Hi there,

I am an 18 year old car enthusiast currently restoring a 1980 triumph spitfire 1500 and need some help. I have recently removed the shell and stripped all the gunk and grime off the chassis and given it a new lick of paint. I have however one issue. There are 10 or so chassis bolts that mount the shell to the chassis and I have removed every single one but one. The bolt I am struggling with is in the front offside outrigger that is below the bulkhead. As you may be aware, there are two bolts here. One outboard of the chassis that is not in a threaded shaft and bolts all the way through the chassis to a nut on the bottom side. The bolt that is inboard on the front chassis outrigger, however, is a bolt that runs through a threaded lip on the chassis in the outrigger. This inboard bolt is stuck fast, the head has sheered off, and I am unsure if to drill it out and recut the tread in the lip or something else. I have applied mole grips with the tightest grip possible but I can't get it to budge. I am worried about damaging the chassis without good reason to as well as the crack that is around the stuck bolt.

I have attached a few pictures and I would be very grateful for any advice I can be given on how to tackle the problem.

Fin McCaig








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Ok, thanks for the help, I have applied heat but it wasn't budging. Maybe it needs more???!!! I will try the pilot hole.

Please can you explain what you meant by :

6 minutes ago, Pete Lewis said:

tapping drill size for 3/8unf  8.5mm     5/16   unf   6.9mm  

I know the bolt is a 5/16 unf but what do you mean with the tapping drill bit?

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+1 for lots of heat; don't round it off any further as you need that stub to get any kind of grip on it. Tap it gently on the top, quickly and repeatedly with a small hammer, set up a good rhythm as the vibrations can often break the seal. Tightening it as well as loosening it, just gently back and forth with no great pressure can also free it up.

If you have to drill it out use a very small drill followed by progressively bigger; often the heat will break it free so each time you drill try it again. Last one I did was paper thin by the time it freed up, but there I was able to gently hammer the edges of the bolt away from the surround metal by collapsing it into the hole I'd drilled.

Worst case scenario is retap the hole or else helicoil it.


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Make sure you have it well soaked in penetrating (not WD40) or diesel (seriously) and leave it to work (patience) along with the tapping and heat.  Worry not, we have all been there.  I know about all the 'rules' but I am not that far from you and tel nos is in the book if needed.  From the look of the chassis in the bottom photo doing well so far.


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Ok so I have managed to get the bolt out thanks to your help but now have a new issue! I have now discovered that the threaded piece is a nut thing that was internally welded to the inside of the outrigger. The cracks that I previously spoke about are now clear and attached are a few pictures. Please can I have some advice on what to do now? The nut has half broken away but I was thinking that that might not matter because if a new bolt is put through it will pull the nut back to its original place??




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Best option would be to weld it back first. It might be strong enough to pull back into place - try bolting something to it, a spare piece of metal or odd bracket, before you refit the body and see how strong it is; if it shears, well it's better that way than with the body on, and you'll have to replace it anyway. If it pulls tight again without breaking off completely that's a good opportunity for a small tack of weld to hold it in place.

You can get threaded inserts (Rivnuts?) to replace it, but you'll have to buy the fixing tool as well. If you don't have access to a welder I'm wondering if there's any kind of adhesive that would hold as well as welding?

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Thanks for the help. I will be able to get hold of someone to weld potentially in normal situations however I will struggle at this point in time. Therefore, would a form of JB Weld work. Definitely a bodge but would it work and be safe enough?


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Given that the bolt was rusted in, and the original weld to make the nut captive was cracked, there's so much corrosion about that JB can't adhere to solid metal.

An alternative would be a Rivnut if you have the kit to do it.

I know it would be good to finish the chassis before moving on, but it might be best to.make note, move on and finish this detail when the crisis is over.

Good luck!

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14 hours ago, JohnD said:

Was there really an episode of Binky where the fitted a Rivnut instead of a welded-in captive nut?

Nick must have been away!

The whole series is worth watching, Fin, if you haven't!

I have watched all of the available episodes and am waiting impatiently for the next one! The finish is just superb so far!

I've also watched Escargo - with a new one due out tomorrow. 

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