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Author: Subject: Drilling a broken stud
luke2152

posted on 19/7/19 at 05:54 PM Reply With Quote
Drilling a broken stud

I have a cylinder head with one broken m8 stud for the exhaust manifold. It's broken below the surface. I've tried drilling it but it seems to be very hard. My HSS bits wouldn't scratch it and I tried a new 3mm cobalt one for stainless and it still wouldn't do a thing despite lube and taking it slow. I'm starting to think its made of something fancy like inconel. Any other material I should try? Head is off so I have goo access to it.
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snapper

posted on 20/7/19 at 07:42 AM Reply With Quote
My cousin does this a lot on heavy lorries, there are a number of tricks he uses but in the case of a broken stud below the surface he gets a punch spot in the centre and uses a small drill to start a hole the the options are, if there is room to use a step drill as they are stronger, once you have a decent starter hole you can run a drill to the end of the stud, then progressively use a bigger drill to get close to the threads, should then be able to break it out.

Stud remover bits are brittle and should be used with extreme care.

The second method is to not drill a central hole but to use small drills to chain drill in a circle with progressively larger drills, this method takes up to 3 hours.

This is something I have just come up with, if you can get a bolt of the same thread in the head over the Broken stud then take the bolt out cut it to a short size either leave the bolt head on or cut a slot for a screwdriver then drill the bolt with a reasonably sized drill bit, put that back in the head over the stud and use that as a guide for your first drill into the broken stud

Good luck, take your time, walk away for a break if itís not going your way





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luke2152

posted on 20/7/19 at 01:14 PM Reply With Quote
Thanks but I literally cannot penetrate it with a drill. I tried the mig at work to build up a blob that I would then be able to twist out with vice grips but cant get the wire to stick to the stud. Has anyone had spark errosion done? Is it expensive?
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v8kid

posted on 20/7/19 at 06:25 PM Reply With Quote
try a solid carbide drill at low speed and high feed





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big_wasa

posted on 20/7/19 at 08:48 PM Reply With Quote
If itís only a mm or two below the surface then a washer to protect the face of the item and weld through a nut has worked best for me in the past.

It can take a few attempts but it rarely lets me down.

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nick205

posted on 22/7/19 at 07:59 AM Reply With Quote
quote:
Originally posted by big_wasa
If itís only a mm or two below the surface then a washer to protect the face of the item and weld through a nut has worked best for me in the past.

It can take a few attempts but it rarely lets me down.



I've done it successsfully this way as well on alloy cylinder heads and also on alloy wheels with locking wheel nuts when I didn't have they right tool for them. As suggested, use a washer (penny/repair washer if you have one) to protect the alloy around the stud. It's also (IMHO) good practice to run the right size tap/die over the part before fitting the new nut, bolt, stud. It ensures the thread is clean and free from blockage.

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MikeRJ

posted on 22/7/19 at 09:32 AM Reply With Quote
I had a similar problem on a Fireblade engine, the snapped off studs were stupidly hard and even cobalt drills were skating around. I'm pretty sure this was down to multiple failed attempts to weld a nut to the remnants (one of the few times this has failed for me) so I used a very small dremel grinding bit to create a pit in the middle of the stud and the cobalt drill then managed to start working. However I had two studs to get out and it required three drill bits...

Carbide bits are incredibly hard, but they are also very brittle. If you snap one off in the stud you are in a for pain, spark erosion is the only thing that's likely to save you at that point.

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miskit

posted on 22/7/19 at 09:48 AM Reply With Quote
quote:

Text This is something I have just come up with, if you can get a bolt of the same thread in the head over the Broken stud then take the bolt out cut it to a short size either leave the bolt head on or cut a slot for a screwdriver then drill the bolt with a reasonably sized drill bit, put that back in the head over the stud and use that as a guide for your first drill into the broken stud



That's a great idea!

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AlexXtreme

posted on 22/7/19 at 08:46 PM Reply With Quote
getting it started if the difficult bit so try a centre punch or as the above suggestion the dremel to create the initial pit.

For cooling, try some water based lubricating jelly eg KY Jelly as I found it works very well at keeping things cool!

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paulf

posted on 22/7/19 at 09:28 PM Reply With Quote
I used to work at a company that did a lot of engine work and often came across studs that we couldnt drill,quite often after a garage had tried to remove them and snapped off a stud extractor .We often found that a masonary drill resharpened like a twist drill would do the job with less chance of snapping the a solid carbide drill.
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