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noah · 25-03-2006, 01:05

every bike uner about £400 comes with a cheap bottom bracket. they are unsealed and prone to breaking. get yourself a new one asap. a shimano un-52 (might have a newer model now) should do the job perfectly, anything posher like the un-72 will be hard to find as they changed the whole BB interface in the last few years.

the unit should be around £20 and fitting should be £10-15. you'll need to take the bike in as BB's commonly come in 2 different shell sizes and any number of different lengths and it's important you get exacty the right one to within 2.5mm or your gears will sufffer.

this is all presuming it is the BB that is the problem, the other potential is that the crank arm has come loose, you'll know this if it is just one side wobbling not both. if this is the case you'll need to tighten it up and if it keeps coming loose you'll need a new crank and BB as the splines will be worn.

hope all that helps, oh and yeah, i used to be a bike mechanic

edit: they should all be the same type of thread with drive side normal and non drive reverse thread unless you have and italian bicyle, they're backwards!

25-03-2006, 01:05	#7 (permalink)
noah Been here a while Join Date: Sep 2005 Location: cardiff and bristol Posts: 414	every bike uner about £400 comes with a cheap bottom bracket. they are unsealed and prone to breaking. get yourself a new one asap. a shimano un-52 (might have a newer model now) should do the job perfectly, anything posher like the un-72 will be hard to find as they changed the whole BB interface in the last few years. the unit should be around £20 and fitting should be £10-15. you'll need to take the bike in as BB's commonly come in 2 different shell sizes and any number of different lengths and it's important you get exacty the right one to within 2.5mm or your gears will sufffer. this is all presuming it is the BB that is the problem, the other potential is that the crank arm has come loose, you'll know this if it is just one side wobbling not both. if this is the case you'll need to tighten it up and if it keeps coming loose you'll need a new crank and BB as the splines will be worn. hope all that helps, oh and yeah, i used to be a bike mechanic edit: they should all be the same type of thread with drive side normal and non drive reverse thread unless you have and italian bicyle, they're backwards! Last edited by noah : 25-03-2006 at 01:08.