Thread together PF bottom brackets: why the recommended torque so high?

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musiclover
Posts: 494
Joined: Mon Sep 30, 2019 11:58 pm

by musiclover

jpeterson1012 wrote:
Sat Dec 04, 2021 6:23 pm
I've actually snapped one of those thrad-togethers straight in half by torquing it to the recommended spec.
Which one and what was the torque?

PS just as I though. Thanks for the feedback.
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takolino
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Location: USA, SF Bay Area

by takolino

Adding another data point to manufacturer's torque specs for thread together BBs. Ninja-Lite BB requires only 10-12 Nm. Mine hasn't come loose, yet.
https://www.tokenproducts.com/bottom-br ... ethod=view
I agree to two points in previous posts. On the high torque, I can see how unsupported BB shells in carbon frames where the bb shell area is hollow and the two bores do not connect, it can flex and cause problems. Also, if the faces are not parallel, it's not going to be aligned, thread or no thread. I had to face an Aethos to get the crank to spin freely.
My recommendation would be to check bb shell for squareness and face if needed. If your bb shell is not a continuous tube, I woudn't use a thread together bb. The unsupported area of the shell will give a bit, forcing the bearings to go out of alignment. I would use pressfit instead.
jpeterson1012 wrote:
Sat Dec 04, 2021 6:23 pm
I've actually snapped one of those thrad-togethers straight in half by torquing it to the recommended spec.
Curious what frame that was on. Light carbon frame? My guess is that the high torque caused the bb shell to compress unevenly and created a bending force on the bb threads. Reminds me of how easy it was to snap seatpost binder bolts on old steel frames. similar bending forces.

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musiclover
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by musiclover

Well, since I have discarded my Chinese noname thread together BB and bought Ninja, and since my frame cup is not a continous pipe once I will install the Ninja I will be able to conduct a practical experiment to give the answer to that exact question.

The simptoms of not being able to push the shaft easily through the bearings and rotation without load with a bit of resistance probably indicates bearings misalignment, but I am still running the Chinese BB until Ninja arrives.
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DJT21
Posts: 381
Joined: Sun Mar 27, 2011 7:35 pm

by DJT21

I have no idea about the high torque values, but I had one of these think it was a Praxis) in a push fit frame and it creaked. I replaced it with one of those press-in FSA BSA threaded sleeves - no more creaking and I could then use regular threaded BB cups that're much more cost effective.

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