How should I repair a cracked trough roof beam?
The right way to fix this is to have a local engineer size a LVL (laminated veneer lumber) beam for you (solid wood lumber won't meet modern standards for a span that long). It'll likely be taller than your current beam. You'll need to temporarily support all the rafters with a framed wall on each side, using double top plates. Keep them a few feet away from the beam to allow room to work. Remove the existing beam, the posts supporting it, and all metal hangers. 

The new beam will likely be 2" thicker than the current one--LVL beams are often 1-3/4" thick per member, and they're usually doubled in cases like this. This will require trimming of the rafters on one or both sides. 

Slide the new beam into place and support it a few feet from each end with temporary posts. Fit new posts using adequate lumber. Double 2x4s may be enough, but ask the engineer. Install the same hangers if they're appropriate, or use new ones. 

Alternatively, you may be able to install your new beam directly below the existing beam. Of course, this dramatically reduces headroom. I expect a new beam to be sized at around 12" high.