how do you ...............????

[MAXTHEROTTI]

so the crank is listed as a 107 to a 113
do i take a stab at 110? or go for the 113 seeing as its a dale and has fatter tubes?

rob

and i have no old bb,s kicking about to try that method

 

[one-eyed_jim]

Yeah how is it worked out. Good question.

A given pair of cranks is matched to a certain bottom bracket axle length. There's usually a narrow range of axle lengths that will work - one that gives the ideal chainline, and a slightly longer one that allows for oversized chainstays, or for the fact that the front derailleur sits a little further out on an oversized seat tube. For "low profile" cranks where the arms flare outward from the spider, it's usually 107mm-113mm. For older cranks it's normally 120-130mm. You can work it out by installing the cranks on any old axle and adding or subtracting to get the right chainline, but it's easier to look it up.

If you know what you're doing, you can sometimes play with the specs a little, for example using a shorter axle for a 2x9, or to reduce the chainline and Q with smaller chainrings.

The shell width (68mm or 73mm) is determined by the frame, so you can simply measure the bottom bracket shell width with a ruler.

 

[one-eyed_jim]

so the crank is listed as a 107 to a 113
do i take a stab at 110? or go for the 113 seeing as its a dale and has fatter tubes?

113 is the safe choice. 107 might work, but if I were you I'd wait for someone with that frame and those cranks to confirm. I've got a feeling that the 110mm axle is slightly asymmetric, so it may not be the best choice for your situation.

 

[FluffyChicken]

For these old (and shimano's original) super low profile cranks, then the 107 gives the ideal chain line of 47.5.

Only use the wider versions if you need to (see points given before).


UN-54 would be the modern LX one (UN-5x)
http://www.parker-international.co.uk/6 ... er=froogle

 

[russ77]

I as trying to work this out myself earlier today. It also turns out that there were two versions of Octalink crank/BB pattern too, and that getting the wrong one can be disastrous (well, enough to cook your cranks anyway).

Anyone know how to make sure you're getting the correct Octalink pattern?

 

[one-eyed_jim]

It also turns out that there were two versions of Octalink crank/BB pattern too, and that getting the wrong one can be disastrous (well, enough to cook your cranks anyway).

Anyone know how to make sure you're getting the correct Octalink pattern?

Octalink ain't retro, dude.

Well, I guess it might be.

There are two spline patterns, one used for XTR and all road cranks, and one used for all mtb cranks except XTR. That's the serious compatibility issue.

Then there are a variety of axle lengths. Road cranks use 109mm for a double, 118mm for a triple. MTB cranks are 113 118 or 121mm, depending on model and chainline, except XTR which came in 112 and 116mm versions. You can obviously get away with certain combinations of XTR cranks and road bottom brackets (and vice versa) if you have particular chainline requirements.

The non-XTR mtb bottom brackets have ES part numbers - ES51, ES71, etc.

The other units have BB part numbers that correspond to the group they're part of: BB 5500 (105), BB M-952 (XTR), etc.

That do you?

 

[Konaglider]

I recently got an Orange Prestige of the 'bay, has LX 563 cranks and came with UN71 115 mm BB. I admit I didn't check exact chain line before I've dismantled for re-build, but sure it's 'right' .

 

[russ77]

Octalink ain't retro, dude.

Sorry for that. Promise to hide it well.

That do you?

Certainly will. Thanks very much for the advice.

 

[MAXTHEROTTI]

I recently got an Orange Prestige of the 'bay, has LX 563 cranks and came with UN71 115 mm BB. I admit I didn't check exact chain line before I've dismantled for re-build, but sure it's 'right' .

hmm according to the list the bb should be 107 to 113 tho??
no mention of 115 for the 563,s?
i am fairly sure that looking at the sheldon brown chart i need a 113 due to my frame having bigger tubes :?
rob

 

[Konaglider]

May be the case I've got 110mm and 113mm BB's so will have to check myself when 'in the shed'. Doing other project at the moment . As you say, frame design etc plays a part, as does if you use larger sprockets or smaller more regularly, length of BB chosen gives you a bias toward either end of cassette with a 'happier' chain line.
My Orange is 7 speed, maybe that plays a part in it having 115mm.