Hollowtech BB tightness

[roubaixtuesday]

Bought a new BB as the old one had lots of play in it. But, on investigating, just tightening the plastic nut that brings the cranks together solved it (after having loosened off the crank). Presumably it had just loosened off a bit in use - probably done about 5000 miles.

So far so good.

The question I have is how tight should it be? I found that barely finger tight resulted in slight resistance to rotation, and I wonder if the thing will just back out.

Advice please - how tight should the plastic retaining recessed nut be, and would resistance to turning the cranks be expected at barely finger tight?

 

[ianrauk]

I tighten as much as I can by hand then back off a tiny.
That works for me.

 

[figbat]

The plastic tool I have has a torque value on it - from memory it’s ~2 N.m but this is useless since there’s no way of getting a torque wrench on it.

 

[Tenacious Sloth]

According to Shimano it should be 35-50Nm.

https://si.shimano.com/pdfs/dm/DM-RAFC001-03-ENG.pdf

or do you not mean the BB halves?

 

[roubaixtuesday]

According to Shimano it should be 35-50Nm.

https://si.shimano.com/pdfs/dm/DM-RAFC001-03-ENG.pdf

or do you not mean the BB halves?

Thanks for the reference, appreciated.

That torque is for the actual BB itself.

I'm referring to what I now know, thanks to your doc, is called the "cap".

The torque specified is 0.7-1.5 Nm (it's a finger tightened plastic tool), page 17.

But like I say, in reality it's more "how do I know if this is right" - a little bit too much results in sight resistance to turning the pedals, and not enough leaves play in the BB. And just right seems suspiciously lose to me at least.

 

[Tenacious Sloth]

I tend to tighten them about as far as I can by hand using the plastic tool.

In fact, I think the tool is provided so that you can’t actually over-tighten.

A slight resistance felt whilst turning the cranks by hand will have no effect at all when peddling and I would have thought negligible effect on bearing life either.