slipping bottom bracket?!

crown of storms

hello all! this is my first time posting here but i have being enjoying this forum for quite some time!

i have a fairly new bianchi pista which was going fairly good until after a sudden exertion i felt the bottom bracket slip, this has since been re-occuring every now and so often when i pedal particularly hard or back pedal. i took it to my lbs and had the lock ring tightend and chainset inspected for problems- the problem continued. i have since upgraded from the stock chainset and the problem persists! the only remaining common denominator in my drive train is the frame as all other parts have been upgraded!

any help/ advice would be greatly appreciated!

thanks.

CheGuedara

If you're experiencing slipping forward of the cranks as you're pedalling/putting power on maybe consider having the rear hub checked out and serviced for dirt/wear affecting the freewheel mechanism. That sounds like your problem. What bike shop did you bring it to out of curiousity - this should have been picked up easily by a good mechanic

*sorry just after realising its a fixie - almost certainly the chain so, oops*

niceonetom

CheGuedara wrote: »

If you're experiencing slipping forward of the cranks as you're pedalling/putting power on maybe consider having the rear hub checked out and serviced for dirt/wear affecting the freewheel mechanism. That sounds like your problem. What bike shop did you bring it to out of curiousity - this should have been picked up easily by a good mechanic

*sorry just after realising its a fixie - almost certainly the chain so, oops*

actually i think you might have been on to something the first time.

OP are you sure the problem is at the BB?

a slipping sensation can be a sign that something is awry with the cog/lockring on the hub. if the lockring isn't tight against the cog the cog can unscrew when you apply backwards torque (skids or leg-braking). then it tightens again when you apply enough forward torque (maybe when standing to sprint or accelerating hard from a stop?). the sensation is that of the pedal dropping away beneath you for a fraction of a second, as if the chain dropped and is not nice at all... sound like what you've been experiencing?

make sure your lockring is good and tight - and remember that it is reverse threaded; but i'm sure you already knew that.

crown of storms

niceonetom wrote: »

the sensation is that of the pedal dropping away beneath you for a fraction of a second, as if the chain dropped and is not nice at all... sound like what you've been experiencing?

yea- i think that's it.
thank's a million for all the help!

blorg

I have this on my own fixie, the lockring threads are stripped so the cog is only held on by itself. In normal usage pedalling forward will serve to tighten the cog so this is not a major problem. You are OK indefinately with this setup if you don't try to skid stop and use the brakes instead. However, as I have found to my cost a number of times, exuberant skid stopping can unscrew the cog entirely. Before you get to this point smaller skid stops can unscrew a bit so that when you go to start again you get a slipping sensation exactly as you describe as the cog tightens back up a bit.

crown of storms

blorg wrote: »

I have this on my own fixie, the lockring threads are stripped so the cog is only held on by itself. In normal usage pedalling forward will serve to tighten the cog so this is not a major problem. You are OK indefinately with this setup if you don't try to skid stop and use the brakes instead. However, as I have found to my cost a number of times, exuberant skid stopping can unscrew the cog entirely. Before you get to this point smaller skid stops can unscrew a bit so that when you go to start again you get a slipping sensation exactly as you describe as the cog tightens back up a bit.

that's it exactly! thanks a million- i can rest easy now- i'll just ease off the mad skidz:p