Idiots guide to broken bolt repair

[Murv]

I have a sheered off bolt in a heat exchanger that I need to somehow repair.
The bolt snapped with very little pressure on it, which is understandable looking at the corrosion on the surviving part alongside the one that came out OK.
There doesn't seem to be much chance of getting the rest of the stud out, I drilled into it and hammered a sealey stud extractor in which subsequently snapped when force was applied to it.
It's also been soaking in plusgas for a week and had liberal applications of a blowtorch before I started on it.

Can I just drill down through the old stud, then wind a tap into it? I'm guessing a helicoil wouldn't be of any use due to limited material thickness on the heat exchanger?
But, as you may all remember from threads past, I know nothing about this sort of stuff!!

So, what do I need to buy to make this better, and any sort of idiots guide would be greatly appreciated!

 

[KenMcCulloch]

I once watched a very skilful engineer (with impressively steady hands) spot weld an Allen wrench onto a broken exhaust manifold stud. This was done without any damage to the threads in the tapped hole in the cylinder block. I would look for a similarly skilled person and give them some money to extract the remainder.

 

[PaulRainbow]

Hope you haven't still got a bit of the stud extractor in there, it wont drill.

Drill it out as carefully central as possible. Try hammering a torx or spline tool into it, but do not break one off in there. If that fails you'll need to drill it out. A helicoil is, as you say, unsuitable.

You might be able to drill it out well enough to run a tap through the last remnants of the old bolt, but the threads may be a bit delicate, so i'd fit a short stud in there with Loctite retainer. If it won't tap clean enough for that you could use a 10mm to 8mm stepped stud, again using Loctite retainer.

Example of a stepped stud : https://www.torbaylambretta.co.uk/Stepped_Type_10mm_to_8mm_Crankcase_Side/p525714_17766898.aspx

 

[RichardS]

Hope you haven't still got a bit of the stud extractor in there, it wont drill.

Drill it out as carefully central as possible. Try hammering a torx or spline tool into it, but do not break one off in there. If that fails you'll need to drill it out. A helicoil is, as you say, unsuitable.

You might be able to drill it out well enough to run a tap through the last remnants of the old bolt, but the threads may be a bit delicate, so i'd fit a short stud in there with Loctite retainer. If it won't tap clean enough for that you could use a 10mm to 8mm stepped stud, again using Loctite retainer.

Example of a stepped stud : https://www.torbaylambretta.co.uk/Stepped_Type_10mm_to_8mm_Crankcase_Side/p525714_17766898.aspx

I can't really see the broken stud because the cover plate still seems to be in place but as Paul says, you must try and get the broken extractor out. If that is still in there you will need professional help.

As Paul also says, if your hole is central or very close to it, then keep drilling out very carefully until you are using a bit only 1mm smaller that than the original stud. As you use that bit you might well find a spiral of old stud comes out of the hole or you can just see the end of the spiral and you can pull it out with needle-nosed pliers.

If you don't see any spirals then gently introduce a tap exactly the same as the original stud into the hole and, very carefully using a left and right motion with constant removals, get the tap to locate into the original thread and use it to clean out and withdraw the old stud thread until the entire depth of original thread is restored.

I've done this dozens of times and it virtually always works .... but you have to start with a fairly central hole rather than a snapped extractor.

Richard

 

[Daydream believer]

From the picture it seems to have broken flush with the fitting. If you remove the fitting first you may have enough of the old stud extractor to grip with mole grips & gently remove first.
You can then drill the old stud out. One can purchase drill bits with a left hand spiral instead of right hand which, if you can reverse you drill, may suddenly draw the stud out whilst drilling.
The main thing is to drill centrally, Perhaps insert a short wooden plug cut flush then use a small drill to get a central hole. Even a small nut dropped in the hole may get you a start. You may have to put it on a stud, spin it in a drill & grind the corners off first. Then place it in the hole & use it as a guide. Main thing is to ensure that you hold the drill straight & do not wave it about like a flag in the wind when drilling.

 

[steveeasy]

Do you or can you get better access to the stud by removing the other two bolts. looks as if these three bolts hold down a plate. You may be able to extract the tool still in there. more heat? and then a larger better extractor may work. ive used sealey extractors and thought they were rubbish.

Steveeasy

 

[mlines]

Make it someone elses problem??

http://threaddoctorservicesltd.co.uk/

 

[pvb]

Make it someone elses problem??

http://threaddoctorservicesltd.co.uk/

Rather a long way from Kent!

 

[snowbird30ds]

I would be inclined to take the whole lump off first and take it to someone with a tig welder, take the other screws out first with heat if needed (lots of heat, don't be wussy about it), weld a nut over the top of the extractor and remove opposite to it's own thread(let it cool first), then fill the hole with weld and weld a nut over the remains of the stud, let the whole thing cool down then heat the housing and try and remove the stud, welding the hole up tends to pull it inwards slightly making it looser as the weld cools.
I've got away with lots of thread removals like this and if all else fails that looks like it would take a helicoil fine as they don't need much thickness.
I'm assuming an aluminium housing but happy to be corrected.
Edit to add: I don't like extractors as by their nature they grip by expanding the original thread making it tighter in the housing, welding a drilled hole makes it smaller and looser.

 

[Phill]

Rather a long way from Kent!

I’ve a business in Kent and he’s been out to us a few times. His equipment and knowledge is 1st class.

 

[smithy]

If the heat exchanger is aluminium take a look at this video https://www.youtube.com/watch?v=fqZYgReuywM

 

[pvb]

I’ve a business in Kent and he’s been out to us a few times. His equipment and knowledge is 1st class.

Sounds possible then.

 

[lw395]

Google 'alum bolt removal'.
Chemical weapons.

 

[Murv]

Thanks all, much appreciated.
Just to answer a couple of points, the extractor isn't in there, the broken part is somewhere sown in the bilges.
With that plate off, it does give better access, but the broken stud is approximately 10mm down from the top of the fitting.
The picture shows it reassembled as I had to move the boat yesterday.
I will give the thread doctor call tomorrow, on the off chance he may be able to get down, otherwise I'll have another go at it next weekend.

Thanks again,

 

[fisherman]

Surely you have a parted off something in the top of the hole. remove the whole thing and maybe you can get that out, then you're looking at the sheered bolt further down which may respond to an eezi-out.