Broken stud - drill out and retap or stud extractor?

[peakrock]

One of the exhaust studs sheared as I was removing the exhaust headers from my Norge donor bike engine. The nut had rusted solid onto the stud and it sheared the stud about 10mm proud of the head. I tried welding a nut onto the end of the stud but it just took a bit more off the end of the stud when I tried to undo it.

So, I managed to grind the end of the stud flat, centre punch it and get a 1.5mm drill all the way through the stud and the hole is as near central and parallel (surprisingly for me!) as makes no difference. I also have a new left hand drill bit and a new good quality Dormer stud extractor, but I'm not sure whether to use them, as I've had stud extractors break in the past and leave a hardened stub in the hole which really makes life difficult. Admittedly they were not as good a quality as a Dormer one but you get my point.

The alternative is to carefully drill out the stud until I just reach the top of the threads in the head and try and clean them up with a tap or similar. If that doesn't work I can always have the hole drilled out bigger for a helicoil.

My question is: based on your own experience what do you think offers the best chance of success? (I won't hold anyone responsible if it doesn't work! ?

Dave

[Throwley]

I have a fair bit of experience with 'Easyout' stud extractors. None of it has been good. I've not used them since having to shell out for spark erosion to remove the inevitably-broken one from an irreplaceable bit of Laverda.

The only ones I've used which have been any good have been parallel-sided hardened rods with sharp-edged square flutes. Like a cross between a reamer and a long Torx bit. The extractor rod is driven into a drilling of set size, a matching collar slid over the splines and a spanner used on the collar. I've used these on aero engines, and at a previous job in vehicle design, and all I can remember is that the collar is gold and the set comes in a blue box, but the name is eluding me! And I can't find them at all on the internet. Wish I'd bought my own set rather than borrowing work ones!

However... personally, I'd skip the Easyout and go straight for the inevitable drill/Helicoil (or Timesert). It's an accessible area, and pretty easy to get parallel, especially with a glamourous assistant sighting your drill level up from the side. If you get a few left-hand-twist drills, up to the root diameter of the stud, there's a slim chance the friction heat and grab of the cutting edge will do the extraction for you. It's very satisfying when this happens! And if the hole's properly central and parallel, the remaining threads can often be picked or wound out, leaving a repairable thread in the hole.

Good luck...

[iant-s]

I would agree. On no account try the helix tapered extractor. All they do is screw themselves in deep a tight, expanding the broken piece even more. Then they snap off.
I have had success with a square tapered type with a flute on each corner to give a sharp gouging tooth at each square corner. These dig in without the screwing-in effect.
Use a little heat if you can to expand the aluminium. Left hand drill bits - great but they do tend to just cut!