NEw bottom braket

Neil Smith said:

Dear All,
bike disabled for various reasons - I am wondering if I should replace the
bottom bracket. It is a shimano un72 - this not a model on the companys
website. It is probably +3 years old. Just turning it in my hands it feels
OK. When do you determine when to replace these bottom brakets?
Thanks for any suggestions.

If you can wobble the crank around more than a very small amount then
it's time to think about replacing it.

You might first notice it because the chain rubs on the front mech when
pushing hard on the pedals-- caused by the chainrings moving outside
their proper plane as the axle slops around a bit.

You can distinguish this from the wobble of a loose crank because when
you wobble it by hand the crank on the other side moves too.

There's nothing actually wrong with it slopping about a little bit
except for chain rub and perhaps increased probability of derailment. So
if you don't have either of those problems then leave it on for a bit
longer.

I think the UN-72 is a fairly good quality one and could well last more
than 3 years of quite high mileages.

Thanks for your knowledgeable reply. There was a typo in my original
message. The bracket is out of the frame so I can not apply that test.
Neil
"Ben C" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Neil Smith said:

Dear All,
bike disabled for various reasons - I am wondering if I should replace
the
bottom bracket. It is a shimano un72 - this not a model on the companys
website. It is probably +3 years old. Just turning it in my hands it
feels
OK. When do you determine when to replace these bottom brakets?
Thanks for any suggestions.

If you can wobble the crank around more than a very small amount then
it's time to think about replacing it.

You might first notice it because the chain rubs on the front mech when
pushing hard on the pedals-- caused by the chainrings moving outside
their proper plane as the axle slops around a bit.

You can distinguish this from the wobble of a loose crank because when
you wobble it by hand the crank on the other side moves too.

There's nothing actually wrong with it slopping about a little bit
except for chain rub and perhaps increased probability of derailment. So
if you don't have either of those problems then leave it on for a bit
longer.

I think the UN-72 is a fairly good quality one and could well last more
than 3 years of quite high mileages.

Neil Smith said:

Dear All,
bike disabled for various reasons - I am wondering if I should
replace the bottom bracket. It is a shimano un72 - this not a model
on the companys website.

It's been replaced by the UN73. The UN52 and UN53 are similar too.

Quoted message said:

It is probably +3 years old. Just turning it
in my hands it feels OK. When do you determine when to replace these
bottom brakets?

When there is play or when it feels rough - to an extent that you're not
happy with.

~PB

Pete Biggs said:

It's been replaced by the UN73. The UN52 and UN53 are similar too.

There is no quality square taper bottom bracket left in the Shimano range.
When stock run out that is it. Last year when I wanted to replace one for
a single chainring crank a less common length the LBS could only get
the bottom of the range type.

As soon as you get above entry level Shimano cranks do not use
the square taper so they do not make the spares anymore.

in message <[email hidden]>, Pete Biggs

(') said:

Neil Smith said:

Dear All,
bike disabled for various reasons - I am wondering if I should
replace the bottom bracket. It is a shimano un72 - this not a model
on the companys website.

It's been replaced by the UN73. The UN52 and UN53 are similar too.

Quoted message said:

It is probably +3 years old. Just turning it
in my hands it feels OK. When do you determine when to replace these
bottom brakets?

When there is play or when it feels rough - to an extent that you're not
happy with.

Even OK BBs can feel a little bit rough when there aren't any cranks on -
not feeling rough is better, but a little bit rough may still have some
live in. If there's play, however, bin it.

I've had bottom brackets last well into tens of thousands of miles -
provided you don't land big jumps hard, and don't wash your bike down with
a pressure hose, a sealed BB unit should last many years.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; all in all you're just another click in the call
;; -- Minke Bouyed

UN26 for Alivio, Acera, Tourney.
The more expensive use Octalink and Hollowtech systems.

Neil Smith said:

Dear All,
bike disabled for various reasons - I am wondering if I should replace the
bottom bracket. It is a shimano un72 - this not a model on the companys
website. It is probably +3 years old. Just turning it in my hands it feels
OK. When do you determine when to replace these bottom brakets?
Thanks for any suggestions.
Neil

Take the chain off the rings, hold the bike up in the air a few inches
by the seat tube and give the cranks a good push so they spin really
fast. If there's a grinding noise or it feels rough through the tube,
then that could indicate a worn BB.

Duncan

In article <[email hidden]>,
Duncan Smith
[email hidden] says...

Quoted message said:

Neil Smith said:

Dear All,
bike disabled for various reasons - I am wondering if I should replace the
bottom bracket. It is a shimano un72 - this not a model on the companys
website. It is probably +3 years old. Just turning it in my hands it feels
OK. When do you determine when to replace these bottom brakets?
Thanks for any suggestions.
Neil

Take the chain off the rings, hold the bike up in the air a few inches
by the seat tube and give the cranks a good push so they spin really
fast. If there's a grinding noise or it feels rough through the tube,
then that could indicate a worn BB.

Turn the crank to various positions and try rocking it side-to-side -
perceptible movement is OK but if you can see much movement at the pedal
end it's probably on its way out. Remove the cranks and rotate the axle
by hand - if it feels at all rough it's seen better days. Some cassette
bearing bottom brackets can be serviced - I used to use [censored] which could
be stripped, cleaned and regreased, which would smooth them out and get
a few more miles from them, but most cannot.