BB sizes?!

NickD said:

Hi all,

The bottom bracket on my Kona Pahoehoe has started making grating
noises*, and I've taken this as a sign that it problaby needs
replacing. The problem is determining what size BB I need to replace
it with, without taking it out of the bike. So that I can ride down
to the bike store to buy a new one, if you must know...

Don't need to take BB out, but do need to remove cranks to measure spindle
length (end to end). If fitting the BB yourself then you should be able
to remove & fit cranks yourself, otherwise the bike shop could do that for
you.

Quoted message said:

I've worked out that it's probably a 68mm shell size, but how about
spindle length? The cranks are 2001 LX Hollowtech, if that makes a
difference...

Shimano should recommend a certain default length BB for those cranks. If
the info's not online, you/someone might have a manual/instruction
booklet.

~PB

NickD said:

The bottom bracket on my Kona Pahoehoe has started making
grating noises*, and I've taken this as a sign that it problaby needs
replacing. The problem is determining what size BB I need to
replace it with, without taking it out of the bike. So that I can ride
down to the bike store to buy a new one, if you must know...

Quoted message said:

I've worked out that it's probably a 68mm shell size, but how
about spindle length? The cranks are 2001 LX Hollowtech, if
that makes a difference...

It does make a difference. 68mm is right for the shell. The spindle is
either 113mm or 118mm. Measure from the centre line of the seat tube to the
plane of the middle chainring: if it's 47.5mm you want the 113, if it's
50mm the 118.

ES51 or 71 are both suitable units.

Quoted message said:

* - only when it's under load (ie, up a hill, accelerating etc) and
only a certain way round the crank stroke, usually when the drive side
crank is going from the 1 o'clock to 3 o'clock position. But I've had
the BB for 3 years of mixed riding, so reckon it's probably time to
change.

The bottom bracket may not be kaput. A grating noise at that position could
be the chain dragging on the derailleur cage as the frame flexes, or a
number of other things. Try taking the chain off and turning the cranks by
hand. Do the bearings feel rough? Can you produce any lateral play?

James Thomson

Yep, got the fact that it'll be 113 or 118mm, but haven't a clue about
measuring from the centre line of the seatpost... How does that work
then??

As for the noises, it's a bit of a tricky one. While turning the cranks
by hand there's no noise and they turn sweet as a nut. No grinding, no
play - same as when coasting while riding. And there are no other
indications that it's the BB. Which makes me think it might not, in
fact, be the BB.... Having said that, the chainline is reasonably clear
through the front mech, and (being an Easton frame) the frame's
unlikely to be flexing enough to change that. Well, to my mostly
untutored eye....

I've taken the cranks off a couple of times to clean/ change the
chainset, if that makes any difference. Actually, I'm a bit flummoxed,
which is why I was considering get a cheap(ish) s/h BB in good nick,
fit that and see if it makes a difference. If not, it's back to the
drawing board...

Cheers
Nick

NickD said:

Yep, got the fact that it'll be 113 or 118mm, but haven't a clue about
measuring from the centre line of the seatpost... How does that work
then??

As for the noises, it's a bit of a tricky one. While turning the cranks
by hand there's no noise and they turn sweet as a nut. No grinding, no
play - same as when coasting while riding. And there are no other
indications that it's the BB. Which makes me think it might not, in
fact, be the BB.... Having said that, the chainline is reasonably clear
through the front mech, and (being an Easton frame) the frame's
unlikely to be flexing enough to change that. Well, to my mostly
untutored eye....

I've taken the cranks off a couple of times to clean/ change the
chainset, if that makes any difference. Actually, I'm a bit flummoxed,
which is why I was considering get a cheap(ish) s/h BB in good nick,
fit that and see if it makes a difference. If not, it's back to the
drawing board...

Bit obvious, but have you tightened the crank bolts enough when you put
them back on? Even a slightly loose bolt can produce a hideous creak.
Likewise pedals, chainring bolts and so on. It's worth spending time
checking all these things are tight before you buy a new bottom bracket.

--
Brian G

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

Quoted message said:

As for the noises, it's a bit of a tricky one. While turning the cranks
by hand there's no noise and they turn sweet as a nut. No grinding, no
play - same as when coasting while riding.

I had similar noises which I also thought was coming from the BB...
Brand new (v.expensive) Dura Ace BB later and I still had the noise -
turned out to be the bearings in the freehub :-/

--
Mike

NickD said:

Hi all,

The bottom bracket on my Kona Pahoehoe has started making grating
noises*, and I've taken this as a sign that it problaby needs
replacing. The problem is determining what size BB I need to replace it
with, without taking it out of the bike. So that I can ride down to the
bike store to buy a new one, if you must know...

I've worked out that it's probably a 68mm shell size, but how about
spindle length? The cranks are 2001 LX Hollowtech, if that makes a
difference...

It's a 68mm shell size and 113mm spindle length. I replaced my mates bb
a few weeks ago on the same model bike.

James

doh!

AFAIK I've tightened up the bolts as tight as they should be - my
general rule of thumb is if I can't tighten it any more by hand, it
probably shouldn't be any tighter... But I had considered that, and
tried tightening them further. Chainring bolts are tight, pedals should
be fine.

I'll try tightening everything up again, check the chainline. Bit of a
puzzler, but after reading the responses, I'm inclined to think it
might not be the BB after all. It's been in 3 years, ridden fairly
hard, but still seems reasonably solid, occasional scraping noises
aside...

Thanks for all the feedback.
Nick

NickD said:

doh!

AFAIK I've tightened up the bolts as tight as they should be - my
general rule of thumb is if I can't tighten it any more by hand, it
probably shouldn't be any tighter... But I had considered that, and
tried tightening them further. Chainring bolts are tight, pedals
should be fine.

For square taper type (ie. normal) cranks: If you've never used a torque
wrench (with the correct torque) on cranks then you might be shocked at
high tight the bolts are supposed to be. The bolts wedge the cranks up
the spindle as well as retaining it.

On the other hand, I reckon loose cranks cause clicking or clunking noises
rather than grinding, if any noise at all. BB could possibly be loose
though.

~PB

NickD said:

Yep, got the fact that it'll be 113 or 118mm, but haven't a clue about
measuring from the centre line of the seatpost... How does that work
then??

Measure from the centre of the bottom bracket shell to the centre of the
chainring.

~PB

in message <[email hidden]>, NickD

(') said:

As for the noises, it's a bit of a tricky one. While turning the cranks
by hand there's no noise and they turn sweet as a nut. No grinding, no
play - same as when coasting while riding. And there are no other
indications that it's the BB. Which makes me think it might not, in
fact, be the BB.... Having said that, the chainline is reasonably clear
through the front mech, and (being an Easton frame) the frame's
unlikely to be flexing enough to change that. Well, to my mostly
untutored eye....

I recently had a bike with very similar symptoms, and, with great
difficulty, replaced the bottom bracket, only to find this made no
change at all. The problem turned out to be the drive side rear wheel
bearing which had in fact disintegrated in a truly spectacular way. The
balls were still in there, held in by the cassette lockring (which they
were rapidly destroying) and were just about coping under no load. When
you started pedalling, though, sgrunch, sgrunch, sgrunch.

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

my other car is #<Subr-Car: #5d480>
;; This joke is not funny in emacs.

NickD said:

Yep, got the fact that it'll be 113 or 118mm, but haven't a clue
about measuring from the centre line of the seatpost... How
does that work then??

Not seatpost. Seat tube.

http://www.enchantedlearning.com/devices/bike/label/labelanswers.GIF

Shimano specify two possible spindle lengths (113 and 118mm) giving two
possible chainlines (47.5 or 50mm). If you don't want to remove the cranks
to measure the spindle length directly, you can measure the chainline to
deduce the spindle length.

Chainline is the perpendicular distance between the plane of the middle
chainring and the plane that contains the axes of the main frame tubes. The
centre line of the seat tube is a handy reference line, accessible without
turning the bike over, close to the chainrings, and often has a bottle cage
boss or similar that can act as a reference point. Sticklers for accuracy
measure from the chainring to edge of the seat tube and add the radius of
the tube.

http://www.sheldonbrown.com/chainline/

http://www.sheldonbrown.com/images/measure-chainline-angled.jpg

Quoted message said:

As for the noises, it's a bit of a tricky one. While turning the
cranks by hand there's no noise and they turn sweet as a nut.
No grinding, no play - same as when coasting while riding.
And there are no other indications that it's the BB. Which
makes me think it might not, in fact, be the BB.... Having said
that, the chainline is reasonably clear through the front mech,
and (being an Easton frame) the frame's unlikely to be flexing
enough to change that. Well, to my mostly untutored eye....

"Grating" during the power stroke makes me thing something's scraping the
front mech - the chain, a chainring, even the inner face of the crank. As
others have pointed out though, there are any number of things that can
make a noise when you pedal, and the fact that it's intermittent and only
occurs under load makes it harder to track down. Does it depend which
chainring you're using?

Quoted message said:

I've taken the cranks off a couple of times to clean/ change the
chainset, if that makes any difference. Actually, I'm a bit flummoxed,
which is why I was considering get a cheap(ish) s/h BB in good nick,
fit that and see if it makes a difference. If not, it's back to the
drawing board...

So take the cranks off again. If the BB feels smooth when turned with
finger and thumb, it's very unlikely to be the source of the problem. You
might be well advised to buy a spare in any case: Hollowtech is being
displaced by Hollowtech2, and spare bottom brackets may not be available
for ever.

Sometimes the only way to solve an annoying noise at the bottom bracket is
to methodically strip everything down, clean, grease, and reassemble with
proper torque.

James Thomson