If you get a tight one their a pain, I always give them an overnight soak with a squirt of thread lubricant, then give them a good tap on the top while it is still wet to jar the threads and help the penetrant to soak in, same again the next day then lots of tapping on top and sides of stud to jar the threads again then use a heat gun or flame to warm the alloy then bam do the two spanner trick discussed last thread, if feels tight still and not right then I get someone to tap the top of stud while I do the big turn. Be guided by the feel of the stud.....if it feels like it will break then it will so leave, soak again and lots of tapping the stud etc