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Old 02-20-09, 10:41 AM   #1
ksargent
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Questions about crank/bb replacement

Greetings,

I am considering replacing my crankset on my 93 Giant Sedona ATX (it, along with the FD, is the only remaining survivor of the stock Altus A-10 component set) and I have a few questions:

1. A lot is made of the need to properly match the BB and the cranks - I understand this. Beyond the obvious - spindle length and type (eg. square taper, ISIS, etc.) and bracket shell size - what the factors I should consider here?

2. Chainline: it appears to be that chainline is a property of the crank and spindle length - the BB shell size is irrelevant. True? If I select a BB spindle and a crank which gives a specific chainline (47.5mm, eg) will it be the same regardless of the bike it is used on? Therefore, if I select a crank and bb which, by specification gives the same chainline measurement as I currently have, then I should expect it to be the same when installed - true?

3. Finally - I am looking at the Sugino XD crank which Rivendell sells. I understand that this is nominally a road crank, but suitable for all applications. Are there any gotchas I should be aware of (other than the need to match with an appropriate bb, of course)?

Thanks for any and all help
Ken
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Old 02-20-09, 10:44 AM   #2
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one more question - I have heard that tapping and facing the shell is a must when replacing the BB. True?

Thanks
Ken
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Old 02-20-09, 10:49 AM   #3
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Originally Posted by ksargent View Post
Greetings,

I am considering replacing my crankset on my 93 Giant Sedona ATX (it, along with the FD, is the only remaining survivor of the stock Altus A-10 component set) and I have a few questions:

1. A lot is made of the need to properly match the BB and the cranks - I understand this. Beyond the obvious - spindle length and type (eg. square taper, ISIS, etc.) and bracket shell size - what the factors I should consider here?

2. Chainline: it appears to be that chainline is a property of the crank and spindle length - the BB shell size is irrelevant. True? If I select a BB spindle and a crank which gives a specific chainline (47.5mm, eg) will it be the same regardless of the bike it is used on? Therefore, if I select a crank and bb which, by specification gives the same chainline measurement as I currently have, then I should expect it to be the same when installed - true?

3. Finally - I am looking at the Sugino XD crank which Rivendell sells. I understand that this is nominally a road crank, but suitable for all applications. Are there any gotchas I should be aware of (other than the need to match with an appropriate bb, of course)?

Thanks for any and all help
Ken
1) Is a no brainer, every crank specifies which BB gives it XYZ chainline, failing that you can always throw in one and measure.

2) Yes. Follow the spec and you should be fine.

3) Yes, if you're switching from your mtb crankset with smaller rings to say somethign like the XD double which is probably something like a 52/39, it's very likely your FD may not work with the larger rings.
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Old 02-20-09, 10:51 AM   #4
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one more question - I have heard that tapping and facing the shell is a must when replacing the BB. True?

Thanks
Ken
If the previous BB was hard to get out and/or the BB shell area seems to be contaiminated by rust then it might be a good idea to chase it. Most modern frames won't need the shell to be faced if you are going to run modern cartridge bb's that don't really care about perfect shell face alignemtn like the shimano square taper carts (XD uses square taper).

Stuff like external bearing bb's will need to have them faced as will old cup/cone bb's assuming it isn't already faced to begin with.
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Old 02-20-09, 10:56 AM   #5
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Thanks for the answers. Actually the XD that I am looking at is a triple (48-36-26). I may end up replacing the FD anyway, of course.

Ken
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