bottom bracket advice

Hi,

My bottom bracket is knackared. The axle on the side of the front
sprocket (left side) seems to have shortened meaning my front sprocket
doesn't have enough clearance from the frame so it rubs against my
derailer cable causing it to wear out and snap.

I need to replace the bottom bracket. It is +not+ a new bike.

Here are the specs:

Make: Shimano BB-CT90
Other info: VIA 68 SL
BC1 37x24
YL 116

The model is mentioned on Sheldon Brown's site:

http://www.sheldonbrown.com/bbsize.html

Slightly worring entry:

Altus CT90 Triple 116-121 Square 47.5-50 Recalled! Do Not Use!
See Shimano dealer for free replacement. Compact 1995

I have two questions:

* anyone know where I can get one these?
* how can I know if a different model is a suitable replacement? is this
a good idea?

If I have left out information please let me know and I'll do my best to
get it.

Thanks,

Ben.

--
Registered Linux user number 339435

Ben Fitzgerald wrote:
Hi,

My bottom bracket is knackared. The axle on the side of the front
sprocket (left side) seems to have shortened meaning my front sprocket
doesn't have enough clearance from the frame so it rubs against my
derailer cable causing it to wear out and snap.

I need to replace the bottom bracket. It is +not+ a new bike.

It is a standard 68mm wide BB with a 116 mm axle, English threading.
This is the standard BB size for bikes in UK.

Go to your local LBS and tell them you need a new BB. A standard
UN52/UN53 or if you want metal lock rings, a UN72/73 should be fine.
one of these
http://wiggle.co.uk/Default.aspx?Mai...8922&UberCat=0

http://tinyurl.com/copf9

should be fine. Get the 68 shell, 118mm length, or get your LBS to sort
it for you.

...d




Here are the specs:

Make: Shimano BB-CT90
Other info: VIA 68 SL
BC1 37x24
YL 116

The model is mentioned on Sheldon Brown's site:

http://www.sheldonbrown.com/bbsize.html

Slightly worring entry:

Altus CT90 Triple 116-121 Square 47.5-50 Recalled! Do Not Use!
See Shimano dealer for free replacement. Compact 1995

I have two questions:

* anyone know where I can get one these?
* how can I know if a different model is a suitable replacement? is this
a good idea?

Ben Fitzgerald wrote:
I need to replace the bottom bracket. It is +not+ a new bike.

Here are the specs:

Make: Shimano BB-CT90
Other info: VIA 68 SL
BC1 37x24
YL 116

I would get a Shimano UN73:
from LBS or http://www.chainreactioncycles.com/M...spx?ModelID=49 (115mm
should be ok)

Tools (if not using LBS):

http://www.mwdyason.ltd.uk/shop.asp?..._company=TOOLS

- Crank remover
- Bottom Bracket Tool for Shimano

Also a good idea to refit the cranks with a torque wrench. Some
recommended torque values are on the Park Tools website.

~PB

On Wed, 7 Dec 2005 08:21:44 -0000, Pete Biggs wrote:
Ben Fitzgerald wrote:
I need to replace the bottom bracket. It is +not+ a new bike.
snip

- Crank remover
- Bottom Bracket Tool for Shimano

Also a good idea to refit the cranks with a torque wrench. Some
recommended torque values are on the Park Tools website.

Many thanks to all who replied. I had the necessary tools ready so I
did the replacement myself. I went for a slightly longer axle to make
the crank sit clear of my rear derailer cable and that seems to have
done the trick. Just had a quick ride up + down the road and it felt
good. I would have gone for longer but it's raining!

The /real/ test comes on the commute tomorrow.

Many thanks to all who responded for the good advice. This is the kind
of thing I love news groups for. ;-)

Cheers,

Ben.

--
Registered Linux user number 339435

"Ben Fitzgerald" wrote in message
in...
Hi,

My bottom bracket is knackared. The axle on the side of the front
sprocket (left side) seems to have shortened

....

Bottom bracket axles can't shorten. What's hapened presumably is that
the bottom bracket cartridge has rotated on the threads inside the
shell and moved across.

If the above is total nonsense, then presumably it will be corrected
in short order.

If it's correct then nothing necessarily needs replacement. Only
adjustment. Unless the contact with the derailler wire has caused
serious damage to the chainring.( front sprocket) Which can be
replaced on its own in any case.

Just remove the cranks, and loosen the lockring on the bottom bracket
cartridge and then thread it through so the correct amount of axle is
showing on the chainring side - just try a loose fit to check maybe
and then tighten the lockring.


michael adams

....

meaning my front sprocket
doesn't have enough clearance from the frame so it rubs against my
derailer cable causing it to wear out and snap.

I need to replace the bottom bracket. It is +not+ a new bike.

Here are the specs:

Make: Shimano BB-CT90
Other info: VIA 68 SL
BC1 37x24
YL 116

The model is mentioned on Sheldon Brown's site:

http://www.sheldonbrown.com/bbsize.html

Slightly worring entry:

Altus CT90 Triple 116-121 Square 47.5-50 Recalled! Do Not Use!
See Shimano dealer for free replacement. Compact 1995

I have two questions:

* anyone know where I can get one these?
* how can I know if a different model is a suitable replacement? is this
a good idea?

If I have left out information please let me know and I'll do my best to
get it.

Thanks,

Ben.

--
Registered Linux user number 339435

michael adams wrote:

Bottom bracket axles can't shorten. What's hapened presumably is that
the bottom bracket cartridge has rotated on the threads inside the
shell and moved across.

If the above is total nonsense, then presumably it will be corrected
in short order.

It is nonsense. The crank side is the fixed cup and is tightened up
completely. Undoing this will move the crank out, not in.


...d

"David Martin" wrote in message
oups.com...

michael adams wrote:

Bottom bracket axles can't shorten. What's hapened presumably is that
the bottom bracket cartridge has rotated on the threads inside the
shell and moved across.

If the above is total nonsense, then presumably it will be corrected
in short order.

It is nonsense. The crank side is the fixed cup and is tightened up
completely. Undoing this will move the crank out, not in.


..d


Fair enough.

So how is it possible to account for the fact that the bottom bracket
axle has "shortened" ?

Has it really shortened as the O.P claims ?

Otherwise how is it possible to account for the fact that it presumably
functioned o.k up until recently - the front chainrings were correctly
aligned - and now they're not?

Just asking.


michael adams

....

"David Martin" wrote:

michael adams wrote:

Bottom bracket axles can't shorten. What's hapened presumably
is that the bottom bracket cartridge has rotated on the threads
inside the shell and moved across.

If the above is total nonsense, then presumably it will be corrected
in short order.

It is nonsense. The crank side is the fixed cup and is tightened up
completely. Undoing this will move the crank out, not in.

Shimano have made cartridge bottom brackets that insert from the left
(non-drive side). Ben's BB-CT90 is one of those:

http://bernd.sluka.de/Fahrrad/Shiman...-CT90_1995.gif

So it seems likely that Michael is correct.

James Thomson

On Thu, 8 Dec 2005 01:36:38 -0000, michael adams wrote:

"Ben Fitzgerald" wrote in message
in...
Hi,

My bottom bracket is knackared. The axle on the side of the front
sprocket (left side) seems to have shortened

...

Bottom bracket axles can't shorten. What's hapened presumably is that
the bottom bracket cartridge has rotated on the threads inside the
shell and moved across.

If the above is total nonsense, then presumably it will be corrected
in short order.

If it's correct then nothing necessarily needs replacement. Only
adjustment. Unless the contact with the derailler wire has caused
serious damage to the chainring.( front sprocket) Which can be
replaced on its own in any case.

Just remove the cranks, and loosen the lockring on the bottom bracket
cartridge and then thread it through so the correct amount of axle is
showing on the chainring side - just try a loose fit to check maybe
and then tighten the lockring.

I suspect you may be right. The right hand peddle crank does sit well
clear of the frame now, which may well be because the axle has migrated
to the right. I will try this and let you know.

Thanks!

Ben.

--
Registered Linux user number 339435

James Thomson wrote:
"David Martin" wrote:

michael adams wrote:

Bottom bracket axles can't shorten. What's hapened presumably
is that the bottom bracket cartridge has rotated on the threads
inside the shell and moved across.

If the above is total nonsense, then presumably it will be corrected
in short order.

It is nonsense. The crank side is the fixed cup and is tightened up
completely. Undoing this will move the crank out, not in.

Shimano have made cartridge bottom brackets that insert from the left
(non-drive side). Ben's BB-CT90 is one of those:

http://bernd.sluka.de/Fahrrad/Shiman...-CT90_1995.gif

So it seems likely that Michael is correct.

I sit corrected..

...d