Bicycle Mechanics - Ordering new bottom bracket and cranks...
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Hey all! I finally got my crank and bottom bracket tools. I removed the cranks and bottom bracket. The bottom bracket is a 68X124.5 and the cranks are 170mm. Basically what I need to know is how do I order replacements? What would I need to do to upgrade this stuff to isis or octalink? I've been reading stuff all over the net, but I still don't think I really understand the full procedure. I want to thow on some Shimano Deore cranks, but I don't know what BB to get. I looked at this chart http://bike.shimano.com/publish/content/cycle/sac/us/en/technical_service/compatibility_charts/mountain_compatibility.-MainContent-0003-DownloadFile.tmp/mtb%20fc_bb%20chainline.pdf.pdf But it didn't help much. Any and all help is MUCH appreciated.
06-24-06, 12:45 AM
Go to your LBS and say - I want replacements for these things here. And done.
Assuming you're running square taper BB (uh the spindel is square), there's no reason to upgrade to the isis/octalink stuff.
06-24-06, 03:20 AM
I understand the desire to "do it yourself". I really, really like working on my bike and browsing "on line" for bike components. I spend (read waste) hours looking for bike stuff, but I am not at all anti-LBS. I buy as much from my LBS as reasonable, and frequently they are only a few dollars from the online price when you factor in shipping and the wait. I do not take advantage of me LBS. If they help me with a problem, I pay them for the work and buy something as well. That said, you already know what you need to know to buy new cranks and bottom bracket. The more expensive cranksets $300.00+ usually specify the specific bottom bracket that you'll need. The bottom bracket for these is usually proprietary and therefore more expensive. If you're only upgrading to an entry level crank set, Shimano Deore, you may have a couple of choices on bottom bracket model plus generic models. You will probably never revisit your bottom bracket so get the best one you can afford, which means staying with Shimano. The crankset you purchase will only take either square taper, octalink or ISIS. You can't interchange them. If you buy the cranks mail-order , buy the bottom bracket at the same time, and specify that it's for that crankset. The mail order on-line catalogs almost always specify the compatibility of the "generic" bottom brackets as well as the name brand models. If you but from Ebay, search the online catalogs for the correct bottom bracket model for the crankset your planning to bid on. Lastly, the theory is that the octalink gives better contact and better energy transfer that the square taper spindle. Some riders "swear" they can feel the difference. The ISIS is just another twist on octalink presumedly because of patent issues. I don't think there's a big issue with getting the cranks off from any of them, but if the crank bolt or lock ring is alloy, it's possible to strip the treads getting the crank arm off. Finally, you DO NEED a torque wrench, one in "inch pounds", to put on a crank set. This adds $30-50.00 to your project, and may make you LBS a little more attractive.
06-24-06, 07:10 AM
Step 1. Sometimes 1 measurement is worth 1,000 guesses. Measure the width of your bottom bracket shell (Probably 73mm). Measure the distance between your rear dropouts (Probably 135mm).
Step 2. Pick out the crank that you want. New cranks will generally recommend a bottom bracket spindle length. XT octalink cranks, for example, suggest 113/118 spindle.
Step 3. Pick a bottom bracket that matches both your bike's frame and your new crank. There are three things to consider:
a. Spindle interface: Has to match your crank. There are actually 2 different octalinks. For an XT crank you want the V2.
b. BB shell width: Has to match your bike. Go to step 1.
c. BB spindle length: Has to match both. Combine step 1&2. With 135mm dropouts you'll want the longer 118mm spindle length to get the chain line right.
06-24-06, 11:02 AM
His bottom bracket shell is 68mm; he tells you that. His present spindle is 124.5 so the current setup needs that length for a sraight chain line. I was told (that doesn't make it right) that the spindle lengths on bottom brackets are standard from one to the other;:D :D the frame needs the length it needs to keep the chain line straight. I would think he'd want the same length spindle. But to be perfectly honest, I fall a bit short of being an expert.
Thanks for all the input guys! I would have went to the lbs, but we don't really have one on the island(I live on a island in southeast alaska with 3500 people). I've also got the front chainline measurement and it is 50mm, if that helps at all...
Well, I guess I fixed my own problem with all this by getting my chainline measurement. The shimano chart makes so much more sence now!
Thanks again guys!
1 more question. The bottom bracket for the cranks I want says LL113. What does the LL mean? Do I just order a 113 or what?
Thanks SO much y'all!
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