luke2152
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| posted on 19/7/19 at 05:54 PM |
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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
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| posted on 20/7/19 at 07:42 AM |
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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 it’s not going your way
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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luke2152
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| posted on 20/7/19 at 01:14 PM |
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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
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| posted on 20/7/19 at 06:25 PM |
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try a solid carbide drill at low speed and high feed
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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big_wasa
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| posted on 20/7/19 at 08:48 PM |
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If it’s 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
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| posted on 22/7/19 at 07:59 AM |
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quote:
Originally posted by big_wasa
If it’s 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
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| posted on 22/7/19 at 09:32 AM |
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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
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| posted on 22/7/19 at 09:48 AM |
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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
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| posted on 22/7/19 at 08:46 PM |
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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
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| posted on 22/7/19 at 09:28 PM |
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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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