Thanks Chip, I'll give it a try!
George, I don't have an explanation for that either, but the method from that 2nd video did help eliminating the backlash - that is, leave a little space, torque the gear and press the block in the direction as shown in that video, tight the cover, then adjust the spring screw.
Adjust only the spring screw (like in the first video) resulted either no backlash but extremely tight spur gear, or smooth spur gear but also backlash.
P.S. George, actually, I think this is what happened in my case, quote Chip's post: "The most common reported issue is worm bearing block shift."
Yue
