2 replies to this topic

[blacktulip]

whilst working on my girlfriends mini a month ago i came across a stud which was crossthreaded, one of the thermostat housing ones. so...... out came the mole grips.... bad idea, it snapped flush to the head surface. no problem i'll just drill it out...... bad idea...... i cant get the remaining debris metal out of the threads. now im thinking of trying to re thread using a tap. can anyone guide me to the right thread size and anywhere good to buy them?

[dklawson]

Hindsight is 20-20 and I'm sorry this information is coming too late but please file it away for future reference.

If you're lucky enough to have part of a broken stud left sticking out don't immediately start trying to remove it with vise (mole) grips. Heat the offending stud with a propane torch until it's glowing. Quench the stud by spraying penetrating oil where the stud goes in the part (whatever it is). Strike the top of the stud with a hammer with several sharp blows. Wipe the excess oil off and repeat the heat, quench, strike sequence SEVERAL times. After you've done this at least 10 times, spray some additional oil on the stud where it enters the part and grab the stud with your mole grips. Turn the stud to slightly to loosen it. Don't keep going when/if you see it move. Reverse the direction... tightening the stud a little. Then loosen it. Keep going in wider and wider arcs of rotation... tightening and loosening, keeping the stud wet with oil. Eventually you'll be able to back it out.

As for removing the broken stud once it's flush, you started with the correct procedure. Center punch the broken stud as close to center as humanly possible and drill straight through it with a small drill. Use progressively larger drills until you get to a size where you can start to see the threads from the tapped hole breaking through the walls of the stud when you remove the drill bit. When you get to that point use a pick or scribe to pry out what's left of the stud. Hopefully you'll get a couple of coils out. Then clean it all up by re-tapping the hole with the correct tap.

For the record, I remember that the thermostat studs (in the head) are 5/16-18 (someone correct me if I'm wrong). I can't help with sources for the taps in the U.K. (I've got a couple in my garage though)! When you put this back together you may wish to consider using stainless steel bolts instead of the studs. Even if you go with stainless bolts, be sure to coat the threads of the bolts (and their shanks) with either a gasket sealant or anti-seize compound. This will reduce the amount of corrosion that has lead to your current situation.

[blacktulip]

superb, thanks alot mate! ill try picking the last threaded bits out i think first.