I have a relatively new mountain bike with a Truvativ Power Spline bottom bracket. I noticed that it was loose with some lateral movement in the crank arms, so I took everything apart and proceeded to tighten up the bottom bracket.
I tightened the drive side first and then moved round to the non-drive side. As I tightened the cup on this side I noticed that the crank spindle became harder and harder to turn, even after just hand-tightening the bottom bracket cup.
The manual suggests a torque of around 38 Nm on both sides but if I do this my crank spindle will probably jam up completely. In order to keep the crank spindle spinning freely I can only loosely tighten the bottom bracket, i.e. not tight at all.
Has someone experienced this and can offer advice? How can I tighten up the bottom bracket and keep my spindles spinning? Am I missing something?
Thanks
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Does ‘took everything apart’ mean just taking the cranks off? Or did you take the BB cartridge out of the shell too? As the NDS cup only interfaces with the cartridge body tightening it should not affect the bearings. I’d want to inspect the cartridge body.– Argenti ApparatusSep 4, 2019 at 21:54
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"Took everything apart" means I removed the crank arms, then took out the two sides of the bottom bracket. One side is just a cup/threaded ring, the other is a threaded ring with the spindle attached that goes inside the frame.– David RSep 5, 2019 at 9:46
2 Answers
If everything is correct you should be able to tighten both sides to the specified torque without it having any impact on how hard it is to turn the cranks.
From what you describe, it may be that you are missing a spacer on the drive side.
With cartridge style bottom brackets (BB), there is usually a spacer that sits on the drive side between the BB and the frame:
The spacer is not required if you are using a specific type of front derailleur (E-type, they mount using a bracket that you put the bottom bracket through) or if your bottom bracket shell is 73mm.
But without the spacer on a 'standard' 68mm BB shell, the BB sits too far over when the drive side has been tightened and the non-drive side cup can end up pressing against the wrong part of the BB, causing the tightness.
Truvativ BB instructions with the full spacer/non-spacer compatibility chart and explanation about spacer usage and the BB shell size can be found here
If do you want to check the BB shell size, it's the measurement outside edge to outside edge across the width of the bike frames BB shell. If it's 68mm and you do not have a spacer then I would pay a visit to your local friendly bike shop as they will probably have spare spacers or can order you one in.
You should remove the cranks before tightening the bottom bracket (which shouldn't really need tightening). Remove cranks, clean out BB (remove, regrease, etc). Non drive side first, then DS. Fit any appropriate washers (usually Truvativ uses a wavy washer on the DS), insert cranks, tighten to specified torque.
