The shutter speed selection ring is easy to move until you try to set it to 500. It then becomes a bit hard to push. The same goes when you try to push the shutter crank lever. Itís easy to crank at all speeds except at 500 when it becomes pretty hard to push the crank.
This is normal. There is an extra-strong spring that engages for the fastest speed, and that's what you're pushing against. Don't adjust the speed when the shutter is cocked, especially not to 500.