Hey guys, I've been lurking on this forum for a while, but this is the first time I've posted, I'm hoping all of your expertise might be able to help me.

I am pretty new to cycling and working on bikes, but I've always been pretty mechanically inclined and have had a lot of success with all the others repairs and tune-ups I've done so far so decided to try something a bit more involved.

I have a Redline Conquest Pro that I got second hand, it's my first road bike (cyclocross) and it came with an FSA Gossamer crank and FSA Megaexo bottom bracket. I think the BB was original and it finally bit the dust recently. I decided to replace it with a Shimano external bottom bracket as I've heard they have a bit more longevity and I know they work with FSA cranks.

Anyway, the drive side FSA bearing cup came out just fine, however, I had to apply a ton of force to remove the NDS bearing cup and when I finally managed to get it out nearly all of the threads on the FSA cup were stripped and the threaded surface was nearly smooth. I also pulled a bunch of aluminum strands/shavings out of the BB shell which were presumably the threads on the cup.

I took a look at the BB shell threads and they all looked fine, there was no obvious damage so I decided to go ahead and try to install the Shimano cups, again no problem with the drive side, but the NDS cup required more force (probably a sign I should have stopped) but much less than it took to remove the FSA cup. After I had it screwed in all the way, I backed it out again to see if the threads were damaged (yeah, probably another bad idea), and the threads definitely were damaged/stripped, a bunch of the thread surface was pretty smooth again, but some of the threads near the beginning and end survived and the cup seems to still be really tight in the shell.

Is it ok to ride it like this, and if not what can I do to salvage the threads and the frame, like I said I didn't see any obvious damage to the shell threads, but then again I'm pretty new to this.

Thanks for helping a new guy to this forum and this sport
-TK

Take the frame to an LBS and ask them to face the BB shell and chase the BB threads.
This is the one job I take to an LBS because the tools are so darned expensive.
Last time I did this it cost $45 which is likely the high side since it was in Boulder.

+1, let a local shop retap or chase the BB threads. If you have a steel cup with the correct thread, you can make your own chaser by grinding grooves across the threads (like tap flutes) for chip clearance, and running it into the shell to clean out the remains of the old cups. Ince the threads are clean you can install new BB cups. Hopefully you can get a left one without buying a pair.

For future reference, grease BB threads before installing cups and don't force a BB cup in, it'll be hard enough to get out later as is.

Alright, I'll have a LBS take a look at it as I don't have any steel bottom brackets lying around. Thanks for the advice about greasing it, I did actually put a thin layer of some waterproof auto grease stuff I had out in my garage on the threads before I tried to thread it in. Is that ok to use, grease is grease, right?

The grease you have is fine. Only those expecting to leave assemblies together for long periods (years) need worry about upgrading to an anti-seize.

Your problem is that there was probably some residue of the old cup filling the threads, leaving no room for the new cup. The result is that those threads were crushed too. It's also possible that there was a burr or distorted thread in the shell which is what did in the first cup. In any case tapping it clean will resolve the problem.