Square taper BB

Might be a silly question, but here goes...

I don't have much/any experience with square taper bb cranksets. I'm finding my NDS Crank arm is working itself loose over the course of say a one hour ride. If it makes any difference, the crankset has self-extracting bolts.

Google suggests I need to tighten up the crankarm bolt fully, so that the crank is flush with the bottom bracket. However, if I do that, the crank seems to seize up completely and will longer spin freely.

Diagnosis? I'm tempted to remove and replace the bottom bracket - I bought the bike as a beater off here about 5 years ago, so it could probably do with an overhaul. Is there anything obvious I'm missing in the meantime?

If the crank arm is flopping about on the steel axle then chances are the square taper in the alloy crank is toast..... Not the axle.

Yeah, I had thought about that - possibly could have rounded the crank!

Is there a technical reason why tightening the NDS bolt up fully would cause the cranks to seize?

If the crank taper is trashed completely it will ride up the taper if the bolt is tightened until it touches the BB which will stop the crank turning properly. Crank taper has to be pretty much wrecked for that to happen and will. Usually look rounded to the eye.

Thanks, that's really helpful. Will give it a once over tomorrow!

If the bike is a beater then a nds crank can be had for very little money to replace , what crankset us it?

Stronglight 2000 I believe. And yeah, looks like a cheap NDS crank should be easy to come by - not too fussed about mismatching!

Make sure you get either a 90 degree or a 45 orientation crank to match the other side. I thought I could swap two otherwise identical looking sturmey archer cranks before realising one was at 45 degrees to the other.

Thread lock should be used on crank bolts to help stop then loosening.

Thread lock should be used on crank bolts to help stop then loosening.

Periodic maintenance should be used on crank bolts.

What does that involve?

Checking that they are correctly tightened.

I've always found threadlock very useful on bolts I want to stay tightened, which is not to say they don't benefit from being checked periodically too of course.

iirc Shimano crank bolts comes with blue threadlock on them.