Help me out, I have a surly crosscheck frame I am building up for my girl.
I can't get the fixed cup to go in. The BB is from one of my old frames and in good condition.
The threads are compatable (1.37x24). I dont want to strip the threads on either frame or cups.

What kind of bb is it?

Have you greased the threads on the BB?

New frames will often have burs or paint/powdercoat in the threads. Take it to a shop and have them chase the threads.

...and try pushing it in (towards the center of the bottom bracket shell) with a little more force than you'd normally apply as you turn it.

also...do you have a fixed cup tool? (if you don't, go spend the $20. you'll be happy later ps...measure the distance between the flats...it's is either 32mm or 36mm. if you're lucky your lbs will have the double sided tool with both....mine only had a 36 with a bb pin spanner on the other end that i already have)

also...are you turning it the right way? (is it plugged in?)

+1. Drive-side installs counter-clockwise, non-drive side installs clockwise, on most bikes.

Bob