bottom bracket problems.

Simonb256

I have a Giant Bowery 72 (2010) that I use for the ride to work (different route a 9-25miles ride each way). fine.

The problem I seem to be having is that my bottom bracket keeps coming loose. I don't back pedal (except to line up cranks at lights), the threads aren't crossed (so the 'cups' are in the correct way).

This morning it came so loose that the one 'cup' actually pressed against the non drive side crank enough to jam the cranks.

I say cups, but its a square taper BB. The BB seems to now also be dead (with the amount of play), but I assume that's because of having to ride round with it loose.

So with the new BB, I don't really fancy having to resort to threadlock, as this shouldn't be happening??

Am I being stupid here and missing something?

ride_whenever

It sounds like a cup and cone bottom bracket. You can tighten it back up and really tighten the lockring to stop it coming loose. But TBH I'd just put in a shimano cartridge bottom bracket and be done with it.

Simonb256

It is a Shimano cartridge BB, its a shimano UN54. (I should of mentioned this earlier)

The bearing are dead now, but they were fine.

However, the bottom bracket unscrewing itself (on both sides) is by far more of concern.

ride_whenever

That is odd!!!!

Do it up a lot tighter. 40Nm is the stated torque which is loads. And use plenty of grease to nip it up really tight.

Simonb256

They are pretty well greased, (I used to cake stuff in grease, not so much these days).

I'll just have to get a new one and make sure its even tighter, and possibly threadlock it then.

Though, a question has come to my mind, because the bike used to have a 111mm square taper BB before this one, i presume it was a campag.

Whats the difference between Shimano and Campag BBs? I'm not convinced that this would answer the riddle, but it might be a start.

Simonb256

Further to this it appears that BB unscrews in the same direction as I pedal, which i assume is the problem.

Im 100% certain that it's not crossthreaded, so now its a wth am I doing wrong here?

centimani

Ive just had a similar problem on my Trek cartridge BB...beware of the consequences of not dealingwith it soon enough.
Fitted a new one earlier this year, greased the threads, thought i fitted it tight enough. Its worked loose on the drive side. I don't use this bike much and noticed the other day the BBs out a bit from the shell. Hmmm, will tighten that up when i get home. Cranks off, BB was really quite loose, took it out, cleaned up the threads (grease and dust), went to refit...the threads are slightly damaged in the shell.
I can only assume as its wobbled a bit, it's damaged the thread just at the start. It'll hopefully be just a quick run through with a tap to clean it up.

Why did it come loose when the bikes not used much ?...it went in cleanly, i didn't have problems fitting the original, so perhaps i really didn't tighten it up properly in the first place..really properly !!

Simonb256

ok, I took out the old BB this morning, checked the thread and everything seems fine.

I have put in a new BB and will try riding it home this evening putting it through its paces. Seem if I can get an average higher than 20 again.

My chainline is a little off but, thats easy to sort.

Still dont know why the old BB came loose. It seems fine, maybe I just didnt fasten it tight enough last time I stripped the bike?

This time I got out the spare BB tool that uses a socket wrench rather than my usual clumsy hold BB tool in place and use spanner jobby. So im sure its nice and tight.

sumonkhan44

The problem I seem to be having is that my bottom bracket keeps coming loose. I don't back pedal (except to line up cranks at lights), the threads aren't crossed (so the 'cups' are in the correct way).




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