Bicycle Mechanics - talk to me about cartridge bottom brackets
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05-22-09, 01:37 PM
I installed one for the first time last night. I have the tool with the splines on it. The right side, where the fixed cup used to go, went in OK but the tool didn't get a good purchase on the cartridge. I got it tight, but I didn't get it super tight.
1. Is there a technique?
2. Is getting it super tight even necessary?
I ask because taking out the previous bottom bracket, I noticed it wasn't very tight anyway.
The right side thingy where the adjustable cup used to go is PLASTIC. This strengthens my theory that putting this BB in tight isn't important.
3. Is that right?
4. How tight should the plastic thing be?
Ok, I am assuming you are doing this with something like the BB-UN54.
1. Yes. Buy a bolt (forgot the sizing, but basically a very long version of the spindle bolt) that threads through the tool and onto the spindle and you needn't worry about the splines catching. If the bolt is too long, make sure to get spacers. Cost me about $5 at ACE. However, you would need a large adjustable wrench - I think the tool is 1.25" wide - as the hole for the ratchet would be occupied.
2. DS, probably; plastic NDS, not really - very likely to crack anyways.
4. From a lot of accounts, tightening that NDS plastic cup up to spec cracks it. I would just make sure the DS is tight up to spec and then put the plastic NDS side on as far as you feel comfortable that it won't break.
No Tom .... a cartridge BB does not have to be super tight. If your non DS cup is plastic..... I guess it's a Shimano un-54? WTF ... indeed ! You'll notice as you tighten the non DS cup the bearings appear to get very stiff if you set the DS crank on the spindle. I was uneasy about this , but it supposedly does not affect performance.... at least this is what many mechanics have told me. Mine has not failed prematurely, so there you do. It has AL cups, however, not plastic. I've done it both ways.... with light torque and some light thread lock(not the hard core permanent stuff!!).... and with a moderate amount of torque...... and both work fine. Not exactly science, is it?
A tip here.... grease the inside of the cup well, this will prevent creaking between the cup and cartridge.
I grease the threads of both cups, the DS goes in tight. The non-DS can be also used with a touch of touch of teflon tape(pink plumbers tape) if you want to add some security for the mind against loosening of the cup. But really, the BB is a sealed unit.... as long as the cup is in there with moderate torque and is not moving, you'll get no creaking and no worries.
05-22-09, 03:11 PM
I've posted this before but here's my trick for getting the plastic cup in tightly without worrying about cracking it.
First, install the DS and torque to spec (or just get it pretty tight). Now, back it out half a turn. Then, install the NDS plastic cup and tighten it as much as you feel comfortable (~10 ft.*lbs. in my experience). Now, torque the DS to spec.
Using this method, you'll get an extra half turn of tension on the NDS cup without having to actually apply that much torque to it. This has worked for me on several installations of this type of bottom bracket.
05-22-09, 03:18 PM
Yes, it's a UN54.
Thanks, guys! Looks like I'll be reinstalling it. This is for a friend, so I want to do it right.
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