Push the axle pin out whilst holding the block in the palm of the hand to prevent the sheave from falling overboard.
Carefully remove the sheave, noting the arrangement of the washers and rollers.
Grasp the wooden shell with one hand and the strap with the other. Pull firmly in opposite directions to remove the strap.
Clean all parts thoroughly. Examine components for wear. Reapply finish to shells, according to the manufacturer's instructions.
When reassembling, push the strap into the shell until the holes in the strap and the shell line up. Assemble the rollers and washers into the sheave and holding this assembly between the thumb and forefinger, slip the sheave into the shell.
Gently work the axle pin through the hole in the shell so that it passes through the washers, rollers and straps.
Grasp the shell in one hand and the strap in the other and pull them in opposite directions firmly. This locks the axle in place and allows the sheave to clear the bottom of the block.
Refasten the end caps.
Note that this method can be used to mount Conrad Blocks directly to deck hardware, spliced eyes, etc., obviating the need for shackles.