Bicycle Mechanics - Bottom Bracket Facing required?
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03-16-06, 08:17 PM
Thanks for helping with this one.
Installing a UN-72 (cartridge style) BB. As I tighten the cups, the spindle gets noticably griddy. I'm guessing that the BB shell is not square and is tweaking the flange on the drive side cup resulting in misalignment of the bearings with the spindle. I had always guessed that facing is important for loose ball BB and not as important for cartridge style BB's. Am I out of my mind?
btw: the frame is not of quality manufacture
03-16-06, 08:29 PM
That is definately a strange symptom. Is it a new b.b.? Does one cup make it more griddy when tight than the other? Do the cups get hard to turn at some point before they/it is/are all the way in? I wonder if you might need to tap the threads. If the frame was distorted during welding (assuming it's a metal welded frame) the b.b. shell's inner bore diameter might have been reduced. The cups might compress onto the cartridge from this. I've never experienced what you are describing so I'm just speculating.
03-16-06, 08:42 PM
The BB is slightly used my me. The dirve side cup installs without any issues and the spindel turns fine. when installing the non-drive side cup, as the cup engages and slips over the cartridge assemble, the torque required to turn the cup increases. the deeper the cup goes in the bb (over the cartridge assembly) the griddiness gets worse. Note: without the bearing assembly in place, the cup treads into the bb shell just fine. Therefore, I doubt that the ID is being constricted.
03-16-06, 08:59 PM
Note: without the bearing assembly in place, the cup treads into the bb shell just fine. Therefore, I doubt that the ID is being constricted.
Is it one of those grey plastic cups? Those cups could compress enough to fit into a constricted b.b. shell without the bearing unit in place. Once the bearing unit is in there it might resist the compression. Just a thought, not arguing.
Is it the right cup for your frame's b.b shell width? I have seen the adjusting cups get mixed up. You could potentially have a 68mm cup in a box that is labeled for a 73mm b.b. shell or visa versa.
The best thing to do would be to try a new b.b in the frame and see if the same thing happens. If not then your problem is solved.
03-16-06, 09:22 PM
I had always guessed that facing is important for loose ball BB and not as important for cartridge style BB's. Am I out of my mind?
Yes, it's much more critical for loose ball types. Not really very important at all for cartridge types as long as they do not come loose (which should never be a problem with proper torquing - i.e. pretty damn tight).
Headsets are a different story altogether. From the very cheap to the very expensive, all headsets will perform better and last longer if you make sure the faces are exactly parallel to each other. Just a tiny, tiny angle will affect the even distribution of loading on the bearings. With a cartridge type BB there is nothing you will do - short of actually bending the cartridge body itself - that is going to affect the angular relationship between the axle/spindle and the bearings.
"Griddy"? Is that like "gritty"? Is that a Bike Forum thing?
03-17-06, 09:27 AM
With a cartridge type BB there is nothing you will do - short of actually bending the cartridge body itself - that is going to affect the angular relationship between the axle/spindle and the bearings.
This is what I'm guessing as the cause of the problem. but looking at the design of the cups, there is so much lead that the angular play would be minimized. I experimented with this idea by backing off the cup with the flange. 1 turn out (and 1 turn on the opposite cup to retain the same compression on the cartridge), the grittiness went away.
btw: the BB is a UN-72, hollow spindles and alum cups
I believe that the UN-5 series have solid spindles and plastic cups
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