1.
Is it necessary for me to remove the drive pulley to remove the belt?
I have heard that it isn't, but the service manual implies that it is. It also implies that the driven pulley must come off AFTER the drive pulley (is that true?)

2.
what is a good way to measure the 13 pounds of pressure when checking belt deflection?

 

you do not need to remove any pullies to get the belt off. not sure why it "must come off first" i took my driven pulley off and installed the black spring. did`nt touch the drive pulley....

 

My sebsite has instructions for changing the belt. Basically you just turn the pulley with a ratchet while guiding the belt off with your fingers.

Some people get a fish scale to pull 13lbs. I just found a 12lb dumbell, lifted it with my fingertips then just "remembered" how much that was and pushed on the belt the same amount.