I'm not sure how you replace the sheaves with the mast up since, as I see my pictures, all three sheaves are fit onto one bolt through the mast head. When you are up the mast, you are dangling from one of the halyards which puts pressure on the sheave and thus a considerable amount of pressure on the bolt. How do you get the bolt out while dangling from the tensioned halyard? If someone knows how to tie themselves off at the top of the mast safely without having tension on a halyard I'd appreciate the tip. I would like to replace mine. Pictures would be nice if you have them.
Here is a picture of my masthead showing the topping lift sheave (which needs replaced). The single bolt goes through all the sheaves at the top of the mast