Bottom bracket newbie question

[Jimmy2021]

Any idea on how to get it out without damaging it?
Also, would this one I linked fit?
https://www.tradeinn.com/bikeinn/en...KPSsOrT5jEiFviQi2zD97wjYZOrY2dXxoCyooQAvD_BwE

 

[benjabbi]

Screw a bolt into the end of the axle, rest the cup flange on the jaws of a vice and give it a tap or two, it shouldn't be tight, tight.
To be fair, as long as it's not super crusty, you don't usually even need the vice, just grip the cup and tap away.

 

[bikeworkshop]

You'll need to tell us the length of the current axle (assuming you're fitting the same chainset) in order to identify the specific bb to buy.

Italian threads + axle length.

They are available in a few different lengths:

If the new axle is short:
the chainrings can foul the frame,
The downshift can be a struggle.

If the axle is too long:
The chainline is bad, making poor gearshift and noisy and inefficient running
The derailleur can struggle to upshift.

 

[benjabbi]

He does mention he has another identical UN-72 with a BSA cup. Just swap the cups and Bob's your Mothers brother.

 

[Jimmy2021]

You'll need to tell us the length of the current axle (assuming you're fitting the same chainset) in order to identify the specific bb to buy.

Italian threads + axle length.

They are available in a few different lengths:

If the new axle is short:
the chainrings can foul the frame,
The downshift can be a struggle.

If the axle is too long:
The chainline is bad, making poor gearshift and noisy and inefficient running
The derailleur can struggle to upshift.

It's 70mm bottom bracket, both cups right threaded, 122mm long (end to end where crank bolts are fitted)
As it is it looks fine so I suppose it will have to be same size.
This is a picture

 

[Jimmy2021]

He does mention he has another identical UN-72 with a BSA cup. Just swap the cups and Bob's your Mothers brother.

Sorry, my fault.
The other bb I have it's 113mm, so not suitable.

 

[benjabbi]

That looks a bit long to me? If that is an LX M569 or M570 crankset then it should be on a 113mm axle.

 

[bikeworkshop]

So the one you linked

Any idea on how to get it out without damaging it?
Also, would this one I linked fit?
https://www.tradeinn.com/bikeinn/en...KPSsOrT5jEiFviQi2zD97wjYZOrY2dXxoCyooQAvD_BwE

Is the correct replacement if its 122 you need.

@benjabbi makes a good point though - and it looks a few mm long on the ds.

If the replacement bb is Italian std taper rather than shimano, then the chainset will pull on a couple of mm more anyway, but might reach the end of the taper, with disappointing consequences.
You might need to check that.

If you're buying online, I'd advise a UK company.
You can usually tell location by postage times.
Bikeinn is Spanish iirc.

It's a pita if you or they get something wrong, and occasionally the goods get held up in customs, or you get some random charge.

 

[Jimmy2021]

That looks a bit long to me? If that is an LX M569 or M570 crankset then it should be on a 113mm axle.

I'm confused now.
Why would it be on a shorter bb?
The 122mm is the original bb.
Or it depends on what crankset is fitted?

 

[Jimmy2021]

If the replacement bb is Italian std taper rather than shimano, then the chainset will pull on a couple of mm more anyway, but might reach the end of the taper, with disappointing consequences.
You might need to check that.

I don't understand what this means.
Can you please explain?