I am looking for good advise on how to loosen the hread studs without breaking them off.
Stud puller. They put the pressure around the base of the stud not at the top like a double nut. Tapping on the stubborn ones seems to help too, not a heavy hit but gentle firm hits. Plus wax and heat. Penetrating oil helps, NOT WD-40 unless it is the type made for penetrating. Take your time, strong arming is not the way to take them out unless you want to practice drilling the broken ones out. Some times no matter how careful you are, some break.
In the early 70’s I decided to bring my 1937 Cabriolet back to Henry’s spects. I eventually found a correct engine in a junkyard in Brewer, Me that I bought “as is, where is”. When I got it home and began to dissemble it I broke a number of headbolts off flush to the block. It was one of those “aw sh*t” moments for sure. I took the bare block to my local machine shop and Orville said, “come back tomorrow “! I stopped by the next day and it was ready to go! I noticed that there were a number of short broken headbolts on the floor. Each one had a large nut welded to it it. Of course Orville was not willing to tell me how he had extracted the broken studs but when I saw the studs on the shop floor it became apparent to me what his method was. The heat of the weldind process broke the rust bond that broke the studs in the first place! The ten dollars that he charged me was cheap for the lesson I learned.
John