Bicycle Mechanics - Bottom Bracket Questions
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07-16-03, 12:57 AM
Well, I have had my 2000 Cannondale F300 for a couple of years ago, and up until two months ago it was working perfectly. It is really falling apart, I live in New England and there is tons of hilly terrain so you can imagine the general abuse on it would break it eventually. I knew from the day I got it it had junky compenents (SRAM 5.0 rear derailleur, low-end Shimano front derailleur). My rear rim because so badly bent that the spokes started snapping. So while I was replacing the rim, i was going to replace the the rear derailleur and convert bike to a 9 speed cassette and shifters. When i was removing chain, i noticed the crank was badly bent. I have a low end Shimano crank on there now, and i'm going to replace it with a Shimano LX. Will I need to replace the bottom bracket to put on this new crank? If so, does anyone know which size i need, 68mm or 73mm? Thanks in advance.
07-16-03, 02:06 AM
The current LX's use the Shimano Octalink splined spindle, so it sounds like you'll need a new bottom bracket to go with them. If you take a crank bolt out and you see a square spindle, that confirms it.
Measure your Cannondale's bottom-bracket shell edge-to-edge, excluding any parts of the bottom bracket itself, and that should tell you whether you need a 68 or 73... it's simply the width of the frame's BB shell. Hope that helps! :)
BB cartridges also come with different-length spindles (axles), so you will need to take the old one with you to check that you get the right one.
The complication may come if you are getting a new crankset. The offsets (for distance of cranks from the seat tube, and chainline) might be slightly different with new cranks. In that case, the replacement BB cartridge may require different spindle length and offsets from the original.
This is not meant to confuse you, because mech is right with the 68 or 73 measurement of the BB shell. But talk it over with your LBS who should know the answers.
07-16-03, 08:18 AM
usually you want to get a BB and crankset that are from the same "family"
for instance if you get an LX crank, get the corresponding BB. im actually in the same process, supergo has the best prices on a LX BB/crank combo right now.
07-16-03, 09:39 AM
Thanks so much for all the replies so fast! I had already measured it, and that was when i got confused... The actually metal bottom bracket shell is 68mm, but, what really confused me, a little peace of plastic that was appearently part of the bottom bracket that is in there and it meassure exactly 73mm! You can see why i was so confused, I wasn't sure which measurement was the right one. So, if i understand you guys correct, I want the 68mm bottom bracket, correct?
07-16-03, 02:35 PM
Just another question. Which park tools will i need to remove the old crank / bottom bracket and which tools will i need to install the new crank / bottom bracket? Your help is greatly appreciated!
07-16-03, 04:04 PM
A bottom bracket tool. Also, a 15mm wrench for the pedals. Make sure you know which direction the threads go before you start.
07-16-03, 04:20 PM
You said it's a Cannondale right?
If so, it's a 68. Cannondale standard! (Worked in a shop/Cannondale dealer for years)
07-16-03, 04:25 PM
a2psyklnut, do you know which way the threads go on Cannondales? I know it is opposite on either side, i just don't know which side is which.
07-16-03, 04:42 PM
Another question... I am converting from an 8 speed to a 9 speed. Will I need a new front derailleur? I wasn't planning on doing it because the one on there seems to work well enough as it is.
07-16-03, 04:54 PM
Left side is standard threading, no wait, drive side.....no, wait, I can never remember w/o looking at a bike.
Also, an 8-speed front derailleur WILL work with a 9 speed set-up. Not as well, and you'll have slower shifts, but it WILL work.
Left side is reverse threading, yeah, I think!
Regardless, someone will correct me.
07-16-03, 05:28 PM
I just had a thought... I just figured out what chainrings are and that is what i need to replace, so i was tihnking of just getting a set of chainrings instead of a new crank. Can someone recommend me a good set with price in mind? To me it wouldn't be worth paying more than $40 for it, because i can get a whole new crank for about that price that is much better than my current crank. There is really only one set that i found online:
I am sort of ignorant when it comes to bikes, but insticts told me that was a bad brand.
07-16-03, 08:25 PM
Can you get us the model number off the backside of one of your crankarms? That'll help figure out what chainrings are compatible with your crankarms :) These numbers are typically stamped into the inboard face of the arm. Any other info could help too, like if it says Shimano Acera right on the arms.
07-16-03, 08:31 PM
Bottom bracket threading is opposite (left-hand) on the drive side for English threading. I worked for a Peugeot dealer 25 years ago, and I know which side is which.
07-16-03, 08:35 PM
Well, it doesn't say any brand name on it, but Cannondale describes it as a Shimano STX, 22/32/44 teeth. It says CPL-12 on the back of the crank arms. I hope this helps.
07-16-03, 11:19 PM
Does it say FC-Msomething on the rear of the arms? If they're genuine STX of the kind I'm envisioning, the chainring set is not what it appears at first glance, and IMHO you would be best off going back to Plan A and getting some LX's.
07-17-03, 09:56 AM
agreed. you can get a whole crankset with BB for $80. very good investment.
i said supergo has the best prices that I found the other day, but they are all back ordered. Jenson has basically the same pricing, but are all in stock right now. I emailed my LBS for pricing there, but may just go through Jenson
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