Scooterotica

Heated the case with yellow map gas. Then inverted a can of air duster upside down and sprayed that on the stud. It froze it. Huge temp differential. Put penetrating oil on at base. I was going to let sit for 24 hrs and then repeat, but I thought why not try it? I used a stud extractor that pinches at the base and uses a 1/2 in ratchet. 3 out of 4 backed easily out. 4th one snapped. Story of my life. So it's a good technique but let sit over night with some penetrating oil. Repeat next day then remove.

Drill down the centre of the stud, accuracy here is important, the drill size will vary depending on the stud extractor used. You can also use the tapered square end of a file, the bit the handle fit on, and tap it lightly into the hole. Then heat the casing with a gas torch and the stud should screw out.

Use a proper extractor, file works unless it's really tight then the tip breaks off! Use an extractor that's shouldered then chances of it breaking are minimal.

These are the best I have ever used https://store.snapon.com/Multispline-Ex ... 35483.aspx

I would first get some plus gas and let it soak for few days then get a lot of heat into it and try tap it round with a punch first. If that fails then heat and an extractor. If that doesn't work carefully drill out the centre until you have a shell left and then tap it round with a punch.

Those Snap on extractors really look the business much better that the long tapered things I've had varying degrees of success with over the years, think I'll get a set.

If you've got access to a mig welder or a mate who has you could weld a 10mm nut to the top of the stud leave a moment then bust stud should wind out done this a few times with bust studs on jag cylinder heads

Tighten it before you undo it. Don't know why but it really cuts down on the number of snapped studs and bolts