Bicycle Mechanics - ISIS bottom bracket problem
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05-18-07, 02:44 PM
Here is what I am dealing with:
1.New Alum. frame. 68 spacing English threads. Frame was professionally faced and threads chased.
2. New ISIS Stronglight Ti bottom bracket.
3. No obstructions in the frame bb area.
When the BB is installed to proper torque specs. the spindle will hardly turn. Similar to shot bearings. When the BB is out of the frame spins as it should. Threads in but is tight toward the end of the install.
I have done this a dozen times and never had this problem. I can only assume the threads are square to the frame. Any ideas. I will have the threads rechased next week to see if this is the problem.
05-18-07, 03:31 PM
I strongly suspect that if you back off the non-drive-side cup a fair bit, the spindle will turn just fine. Basically, the non-drive-side cup is just there to keep the cartridge BB body from rocking around within the BB shell, leading to chainring wobble and eventually messing up the drive-side BB threads. It doesn't need to be torqued down very hard. Shimano has started making the stabilizing cup out of plastic, which cracks if it's torqued down too much.
Anyway, if you tighten the stabilizing cup too much, it will compress the bearings and lead to bearing resistance. Here's how I explained it in another thread (http://www.bikeforums.net/showthread.php?t=290416) (which was about square-taper BB's but the dynamic here is the same):
My experience with cartridge BB's has mainly been with steel or aluminum stabilizing cups on the non-drive-side, although I've built one bike (http://www.unc.edu/~cupery/pics/bikes/Ari_Schwinn) for a friend with a Shimano BB with plastic stabilizing cup, and also a plastic cup on the bottom bracket on my Centurion (http://www.unc.edu/~cupery/pics/bikes/Centurion_Comp_TA_repainted/).
The non-drive-side cup is there mainly to keep the non-drive-side of the cartridge unit from moving around inside the BB shell (which would stress the shell, and the BB body). It also functions a bit to increase preload on the drive-side threads.
But if you tighten the non-drive-side cup too tight, the bearings get compressed and don't turn as freely. You can easily try this by tightening the non-drive-side cup (if you've got a metal one) and seeing how the spindle becomes more difficult to turn between thumb and forefinger.
So what I've done is tighten the drive-side, which is always steel or aluminum threads, quite tight (I don't have a torque wrench, but it's probably near spec). I'll snug up the non-drive-side a bit, but keep testing the spindle between thumb and forefinger to see if I've increased bearing resistance. If I have, then I'll back off on the non-drive-side cup.
With the plastic cup, I just go by feel and don't tighten it to where I'd worry that it would crack or threads would strip.
It may be worth your reading through the entirety of the other thread.
05-18-07, 05:22 PM
Timcupery is right - back off 1/8-1/2 turn on the non drive cup and it'll probably spin fine. I've had similar experience with other isis bbs. I had a Race Face isis bb that couldn't be used because the slightest amount of torque on the non drive cup would sieze it up. It was also the most expensive bb i ever bought - i think bike parts tend to work that way....
05-18-07, 09:37 PM
Thanks but here is the strange thing: With only the drive side installed and the non drive side in 1/4 the way just to make sure the thing is lined up. Same results. So the issue is with either the threads on the drive side or the BB itself. Because this is a long term project, I am going to install a regular Shimano BB just to see how things go.
I am positive there is no cross threading issues. The other possibility I thought of, is the BB although new is defective. I had this happen with a Deda BB earlier this year. With these sealed BB's there seems to be no way to know if the item is Ok from the getgo.
Thanks again & I will read the complete thread.
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