clunking noise from bottom bracket

[nottscycle019]

Hi, please can you help, when peddling hard on my mountain bike I get a clunking from my bottom bracket. Does anyone know what could be wrong. Thanks.

[Brucey]

the detail will vary with the type of cranks and bottom bracket bearings you have, but in essence something is wrong; the usual suspects are

- the bottom bracket bearings have slack in them. Some are adjustable, some are not and will need to be replaced if they have slack in them. Or

- the bottom bracket is loose in the frame. This should be attended to PDQ as if it is neglected in this state, the frame can be damaged, or

- the cranks are loose where they attach to the BB spindle. Again parts may be damaged.

So wiggle everything about and see which parts actually move. Often the BB bearings are loose where they fit into the BB shell and if this is on the RH side it is difficult to see the movement.

cheers

[nottscycle019]

Thanks, will have a look.

[nottscycle019]

Hi All, decided to change bottom bracket (shimano). I have managed to get both sides of chain set off and the right hand side bottom bracket retaining nut off. I am really struggling to get left side off. Any tips??? I have just left it with plenty of a well known lubricant on. Thanks,

[Brucey]

a picture of what you are up against would be useful.

BTW apologies if this is obvious but the BB threading is LEFT HANDED on the drive side and RIGHT HANDED on the non-drive side. If you don't know this and you are working upside down, this might perhaps explain the 'can't get the LH side out' comment.

cheers

[nottscycle019]

Hi thanks I am managing to move it a bit, few mm at a time. I did look on YouTube before starting. And yes one side is LH And one RH. Going to perceivire might take me while but I think leaving it soaking in penetrating oil for a bit may help. Thanks for the advice so far.

[tim_f]

If you do not have a bench vice, often helps to get friend to hold bike up against fence (or similar) then can apply a lot of force to spanner. (if bracket has hole through may be able to use quick release axel to hold tool on splines.

[nottscycle019]

Hi Everyone, good news, it's took me all weekend on and off, but I have finally taken my well knackered bottom bracket off.

Most of the label has some off or is damaged from rust but I think it is BB 7420. Does anyone know what size I need to purchase and is there a better quality one???

[nottscycle019]

Hi Everyone, just measured to make sure of size, it is 110.5 x 68mm, please help with recommended replacement.

Thanks again for all of you're help and advice.

[tim_f]

If it is a square tapper one then a shimanio UN55

[nottscycle019]

Hi Tim, Thank you, Evans have two brands UN55 & Karyotype JIS. Is one better than the other? Thanks again, Martin

[tim_f]

Karyotype JIS is more expensive but lighter. No experience of it.

The UN55 can be had for about 15.00 GBP mail order. (Evans may price match)

The UN55 lasts for ages and is well sealed. So I would go for a UN55.

[nottscycle019]

Hi Tim, thanks, I think I'll go with the UN55. Thank youagain to everyone that has given advice. I'll let you know how I get on with the installation. Martin

[tim_f]

Remember to use grease or anti cease on the threads, and take care not to cross the threads.

[nottscycle019]

Hi Everyone,

I have just finished installing my new shimano bottom braket, which was easier than taking the old one off. I also cleaned and tightened my chain ring before reassembling it. The videos on YouTube are great for someone that's never done this before. All in with replacing my front tyre and giving my brakes a service it took around an hour. Many thanks for your help and advice. ( I did use copper anti lock grease)