The plan is replace just the bad part of the beam. So I mark the top of the bad part.
And make my first cut with a stiff handsaw. I will use a 2x6 laid on its side, but the bricks are closer to the front than the depth of the 2x6 (1 3/4 inches). So I can't get as deep on that end.
I set my marking gauge.
Marked the depth on the side of the beam.
Now cut down the line as deep as possible.
Obviously the rot had been a problem before. I had to knock out this filler to save my saw blades.
Now to set my saw depth to the depth of my replacement board.
Again the bricks make this a challenge. I did as many vertical cuts to depth as possible.
And now horizontal cuts.
Clean it all out with a wood chisel. Cedar is soft so that's easy to do.