I've searched the forum and can't seem to find the info I need. I am putting on a new chain, wheel with new 8 spd freewheel cassette. Yes, NEW parts on my vintage ride!! But I have hit a snag due to my inexperience.

I have read about chain length, H L and B screws. I am a little confused about how to manage the two variables of chain length and the B screw tension after reading Park's website. But I have a problem before I get to that point so I'll figure that out later.

The RD bolt as I understand should be tight and the "lock nut" on the back should be what binds against the frame thus allowing the RD to rotate forward and backward as needed but no more forward than the B limit screw allows keeping the cogs out of the cassette. That all makes sense. My problem is when tightening the RD bolt the "lock nut" turns and causes the whole derailure to be tight on the bolt so it cannot rotate. I have checked my other bikes and they work as I would expect but I can't seem to trick this locknut into not turning as I tighten. What am doing wrong?

Thanks in advance.