okay it might be your allen wrench. I suppose the wrench size for the knuck is in imperial sizes, if you have an allen wrench in metric size it won't be the same. It will be smaller and when you use it enough it will seem as if it were stripped. If you have an imperial size one, than i dont know haha
Also if you use a torch to expand it, how would that help? If you expand it, that means you put MORE tension on the bolts.