I've only built up three frames previously so I've still much to learn and have never encountered this. Currently building a new frame.
The non drive side BB cup will not go in the last 3mm. Well, it might go in a bit more but it would then be proper man-tight and I fear it would never get it out.
BB cups go in fine up to that point and the thread is not threaded. All the internal thread is being used with it 3mm out. Drive side one is fine.
Any suggestions? Or will it be fine as is? Thanks
Have you got the right spacers in?
Edit like this.... [url= http://www.shimano.com/publish/content/global_cycle/en/us/index/tech_support/tech_tips.download.-Par50rparsys-0017-downloadFile.html/11)%20Crankset%20Installation.pdf ]Link[/url]
Are you sure you don't need to use any spacers? I've got a 2.5mm spacer on each side of my BB. If it's new there should be some instructions with your BB telling you which combination of spacers you need
Have you got the right (or, any) spacers in?
I'll wager that's a 'no'. Will it go all the way in if the drive side isnt in place?
@kraftyslices, 1 each side? You have a 70.5mm bb shell? Normally you use all three spacers (68mm) or just the one (73mm)?
How wide is the BB shell? 68mm?
You need a bigger hammer 😀
Thank you for taking the time to reply. Realise I left out important details:
It is 68mm, which is correct.
Old, square-tapper crank, which never originally had spacers on the first bike.
I don't have any spacers - where would one buy them (if they are required?)?
this style (although not this model):
[img] 
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It Sounds silly, but sure it's not a 73mm unit you've got?
deffo 68
Ah, old style BB, sorry, thought we were talking about HTII BB's.
I'm out.
Yes, it's not unusual for some of the nylon threads to show. Take the drive side out and the see if the non drive side will screw in further. If so, back it off and refit.
Yep not all that odd to see a few turns of thread on the lh cup as long as the drive side is flush with the shell
All should be fine
Brilliant. Drive side is fine.
Thank you for everyone's help - this weekend I will now have the pleasure of building a new 1*10 long travel HT and a rigid SS when I swap some donor parts 😛
what they ( ^ ) said, it'll likely be fine - the NDS cup is "only" there to stabilise the shell inside the frame and is intended to be a tight interference fit. Assuming it isn't somehow jammed in the BB threads it'll be right
I always grease the BB threads of course, but also the inner surface of the cup, to make sure it slides nicely over the main shell and so supports it well. (sure I've read others thinking this is a recipe for creaks but it's worked OK for me in the past)
I fitted a cartridge Octalink bottom bracket to my partner's bike. The drive side (main cartridge) is flush but the resin adapter is showing a thread; it doesn't seem to have caused any problems.