S
Hi all,
have just discovered that the bottom bracket on my MTB has lots of
play and is in need of replacement. On measuring it I also discover
that it has a rather strange size: 68mm shell and 121mm axle (in case
it's important the bike is a Scott Elite Racing MTB from ~4 years
ago). It has the shimano Octalink 8 spline interface and I think it's
probably around the Deore or LX level (cartridge BB) given the level
of components on the rest of the bike (Note: I would check the label/
stamp on the existing BB but I don't currently have the correct tool
in my toolbox to remove it!). It seems that the majority of BBs have
shorter axles of 118 or 113 mm, and the fact that mine is 121mm gives
me essentially no choice for the replacement unit. I had hoped to
replace it with something of an XT or XTR level but it seems this is
not available with a 121mm axle. A few questions:
1) Is there a reason why longer axles aren't offered in the high end
BBs? Is it down to the increased weight or something?
2) Am I measuring the axle length correctly? I assume, logically, that
it is the distance between the ends of the axle, but I guess it could
the distance between the base of the Octalink splines or something?
3) I assume that replacing with a unit with a shorter axle would wreck
the chainline and is not adviseable?
4) I am considering using this as an opportunity to replace the
chainset as well which is also quite worn. I notice that the high end
chainsets come with the BB included, but don't specify dimensions for
the BB. They appear to be universal and work by moving spacers around
to get the right shell width. How does this system cope with different
axle lengths? Is it adjustable or is it one standard size? If so what
is the standard size.
5) Does the group have experience on home fitting of these high end
chainsets. I understand the advice is that you should get the LBS to
"face" the BB shell on the frame to ensure it fits. How essential is
this? I ask because my LBS is some distance away and as a result I
prefer to do things myself where possible.
Sorry for the rambling!
Cheers
Rupert
have just discovered that the bottom bracket on my MTB has lots of
play and is in need of replacement. On measuring it I also discover
that it has a rather strange size: 68mm shell and 121mm axle (in case
it's important the bike is a Scott Elite Racing MTB from ~4 years
ago). It has the shimano Octalink 8 spline interface and I think it's
probably around the Deore or LX level (cartridge BB) given the level
of components on the rest of the bike (Note: I would check the label/
stamp on the existing BB but I don't currently have the correct tool
in my toolbox to remove it!). It seems that the majority of BBs have
shorter axles of 118 or 113 mm, and the fact that mine is 121mm gives
me essentially no choice for the replacement unit. I had hoped to
replace it with something of an XT or XTR level but it seems this is
not available with a 121mm axle. A few questions:
1) Is there a reason why longer axles aren't offered in the high end
BBs? Is it down to the increased weight or something?
2) Am I measuring the axle length correctly? I assume, logically, that
it is the distance between the ends of the axle, but I guess it could
the distance between the base of the Octalink splines or something?
3) I assume that replacing with a unit with a shorter axle would wreck
the chainline and is not adviseable?
4) I am considering using this as an opportunity to replace the
chainset as well which is also quite worn. I notice that the high end
chainsets come with the BB included, but don't specify dimensions for
the BB. They appear to be universal and work by moving spacers around
to get the right shell width. How does this system cope with different
axle lengths? Is it adjustable or is it one standard size? If so what
is the standard size.
5) Does the group have experience on home fitting of these high end
chainsets. I understand the advice is that you should get the LBS to
"face" the BB shell on the frame to ensure it fits. How essential is
this? I ask because my LBS is some distance away and as a result I
prefer to do things myself where possible.
Sorry for the rambling!
Cheers
Rupert