Got a steal 456 frame and trying to fit a new Bottom Bracket. Is one of the fairly standard smbb70 that came with my slx crank. Its all greased, right cup going into right side etc but I can only get it to turn about 1 revolution by hand before I’m needing to bring out the BB tool.

Given on previous bikes I’ve managed to hand tighten it the majority of the way in, I’m thinking I need a different bb size? That or the paint on the threads is causing issues.

or Should I just resort to brute strength?

Could be the paint. My recommendation would be that you take it to a shop and get them to face and chase it for you. The frames aren’t prepared before they are sent out.

On the plus side it’s steel so you’re not likely to damage it with an aluminium BB. But sounds like something is wrong, either the thread is clogged or damaged on one of the parts, or you’re crossthreading it.

If in doubt, quality LBS with a thread chasing tool.

It may well go in fine, but safest to have it chased.

thanks…its not cross threaded as it goes in a few turns by hand so assuming its the correct sized BB its looking like another trip to the LBS.

I’d decided that this would be my first ‘home full build’…bottled out of putting in the Headset with a block of wood and a hammer (probably wisely) but fairly depressing I can’t even get the BB in. I’m clearly the worlds most inept home mechanic, at this rate I’ll probably be going back to get the pedals fitted 🙁

Not your fault at all. Banging in a HS is easy – just keep checking its going in straight.

BTW if the thread is engaging well then it’s the right size. No harm in using the tool to get it in either, just don’t force it. Use grease too.

MTFU. Sometimes you’ve just got to bray on. Its a steel frame so you shouldnt have any problems.

The last two frames i built up, the bb went in fine. My cotic, it didnt, it was stiff. But i ran a knife blade through the threads to make sure they were clean and then just cranked it it.

The last headset I installed didnt go to well. Ended up filing the cup down slightly to make it fit.

All my bikes are solid though and never let me down.

Give the inside of the frame a good clean with wire wool.
The frame should be faced the help the bb live longer though