HEAD STUD EXTRACTOR.

[Parazine]

The set I've used for a long time is a Sealey AK724. Contains 1/4", 5/16", 3/8" and 7/16" extractors. Each also available individually. Coupled with heat at the base of the stud, pretty much works every time.

steve

Agreed.
I find that using oxy/acetylene and getting a lot of localised heat in quickly works much better than fanning it with a DIY butane torch.

c

Agree, oxy/acetylene rather than a butane torch. The block for my new Ulster engine had studs in a worse condition than those in the original posts and all came out without breakages, manifold studs as well. If you do break a stud, the drill guides as detailed in Woodrow work very well when used with the cylinder head. Simple to make if you have a lathe or know someone who does.

Steve

+1 on Oxy-Acetylene. Good and hot then a pair of Vise Grips, tighten slightly first then untighten a bit. Backwards and forwards until you can get near enough 1 complete turn. Then you have a fighting chance but they still will break.....

[A G Wood]

Lots of excellent advice above.
I've done my share of removing recalcitrant studs in various places, so my 20 cents worth:
1.Patience is a virtue, but accept that no matter how careful or adept you are there are some studs that will snap off just to spite you.
2. Use a decent stud extractor, I find the Sealey/Koken roller type is the best. The cam ones like the Sealey VS7232 will lead to disappointment. An oxy-acetylene kit for localised intense heat is a great help if you can access it.
3. Trying to go clockwise on the stud first to crack it loose is sound advice, as is backwards/forwards as it unscrews esp. back off if it starts to bind again.  
4. Balance the force you are exerting on the extractor, I prefer to use a tee handle. 
5. Use a quality penetrating fluid, most of us have our favourite. Even the old timers' trick of heating the stud then melting a candle against it where it threads into the block [allowing the melted wax to capillary into the thread] often works. 
6. If you snap a stud, drill guides [even mild steel ones] are your friend.
7. If you have the kit and the nerve, sacrificing the stud by cutting it down to a stub and arc welding a clearance drilled nut on it [holding the nut down hard on the face of the block] allowing it to cool and then trying it with a spanner is worth a shot.
8. At all cost, avoid the temptation to use traditional ezy-outs on the remnants of badly seized studs, trust me it will end in tears  The only ones worth trying are the splined ones like your Sealey AK724, I have a set of SnapOn/Blue Point  spline type ones and even they have let me down once or twice...

[Bob Culver]

Can often feel when going to break. Is it better to cut off tall so a drill guide sleeve can be made up and fitted over the stump?
Broken seized studs are a nightmare. Turn simple jobs into sagas.

[David Stepney]

I have a baby 6in Stilson wrench. Brilliant on recalcitrant studs. You can get right to the bottom of the stud, which I have found lessens the risk of breakage, and the wrench is small enough to get into most places.

[Chris Garner]

This is exactly why I use a " Blue Point " as I mentioned previously. The jaws can reach the bottom of the stud but unlike a Stilson which is only holding the stud on two opposing faces, the three jaws are arranged in radial symmetry exactly as a drill chuck. Unlike a drill chuck which uses a key, the B.P. jaws are clamped by means of a spanner exerting immense force, so reducing twist and ultimate breakage of the stud.

[Rpm]

Chris, I bought the Blue Point too following your earlier comments and now awaiting its arrival. Noted your valuable experience on this matter Mr. A.G.Wood especially patients

[AustinWood]

It helps if you are able to apply torque to the stud at the same time as striking it on the end. The shock helps to free it.

[jonblob33]

Hi, has no one used spark erosion it always works on a bare block. Used it many times myself,mainly on m/cycles & modern engines. Many general engineering shops do it. A good operator can also cut splines - internal or external to match an existing part. A few years ago I restored an old m/cycle, belt drive but the drive pulley from g/box was missing. Machined a pulley & a local gut spark eroded the splines to suit the output shaft.

[Zetomagneto]

Hi Jonblob, I aquired a block with a stud extractor broken off in it, had it spark eroded which was successful but cost £60. This would be a costly way if you had a number of studs to do.What do you normally pay?

[jonblob33]

I have a local guy, served his time building erosion machines. About £20 per stud. The splines cost about £40. Well worth it.