I found that if you wreck a main bearing and pull a ball out of the race, you can use this on the machined centre in the end of the crank. I found you can get heaps more pressure on the puller and it protects the end of the crank. Once you have a heap of pressure on; give the centre bolt a sharp hit with a hammer, if your lucky it will pop off! (if the boss is on a taper, as Grumpy says with out pic's we are guessing a bit....)
