Author Topic: Bottom bracket torque  (Read 1303 times)

ipswichcycler

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Bottom bracket torque
« on: August 13, 2014, 12:49:18 PM »
I know the bb on a nomad mk2 should be between 10-17nm.  I've read the owners manual and living with a rohloff and it says that is about as tight as you can get with a small screw driver.  I used a torque wrench from local bike shop but not sure what I would do if in the wilds.  What would happen if you were doing it by hand with the thorn bb tool and you torqued it to 20 or 30nm?

Any advice appreciated. Also how small is a small screw driver.

IC

jags

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Re: Bottom bracket torque
« Reply #1 on: August 13, 2014, 01:18:44 PM »
there was know how and FEEL before there was ever a torque wrench, give that torque wrench a drop kick over the nearest hedge and buy a descent spanner.

geocycle

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Re: Bottom bracket torque
« Reply #2 on: August 13, 2014, 01:29:11 PM »
I know the bb on a nomad mk2 should be between 10-17nm.  I've read the owners manual and living with a rohloff and it says that is about as tight as you can get with a small screw driver.  I used a torque wrench from local bike shop but not sure what I would do if in the wilds.  What would happen if you were doing it by hand with the thorn bb tool and you torqued it to 20 or 30nm?

Any advice appreciated. Also how small is a small screw driver.

IC
Hi IC, a confession, I have never used a torque wrench on my bike!  I'm sure they have their place and I'd expect a LBS to use one, I'd also use one on anything carbon.  I've also never touched the BB on my RT/RST they just sit within the Eccentric BB and work for 10's of thousands of miles.  So in answer to your question: she'll be fine!
 

ipswichcycler

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Re: Bottom bracket torque
« Reply #3 on: August 13, 2014, 10:31:58 PM »
Thanks for the replies. I did mean the ebb bolts

il padrone

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Re: Bottom bracket torque
« Reply #4 on: August 13, 2014, 10:38:29 PM »
Torque wrenches are a useful tool, I am sure, but I believe they are mostly required for automotive applications and for carbon fibre bikes. I too have never used a torque wrench on any of my bikes over the past 35 years, including the ones I have personally built up (these have all been steel or aluminium).

The right wrench for the bolt, used firmly but without excess, should not present any problems. My Nomad EBB has a tool for the bolts that is really quite short so I will never over-tighten, even if I haul on it. I don't know anything about using a screwdriver on the bolts - never done this, always use the spanner.
« Last Edit: August 13, 2014, 10:42:53 PM by il padrone »

JimK

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Re: Bottom bracket torque
« Reply #5 on: August 14, 2014, 01:08:34 AM »
I use a torque wrench on those EBB bolts. As I recall, I set it to 10 or maybe 11 Nm. The torque wrench is not really big, so I don't get a huge mechanical advantage. 10 Nm is not super high torque. I would say that using that wrench that came with my Nomad, a good firm twist is about right. I wouldn't go getting my body behind it!

The size of the dent is definitely closely related to the torque, in the range of 10 Nm. Not sure what happens if you go too too high. Ultimately deform the whole structure of the EBB, I suppose. Before that maybe just make dents that are too big so you end up with less closely spaced indents.

Thinking about it a little more... when the axle is at 12 o'clock, the mid-point of the travel, the bolts are hitting the thickest strongest point of the EBB and also the chain-length change per degree of EBB rotation is at a max, i.e. the dents need to be closely spaced. Toward the extremes, 3 o'clock and 9 o'clock, the EBB is thinner, and the chain-length change per degree of EBB rotation is dropping to 0. So the dents will be more widely spaced. There ought to be a nice conclusion to all this logic but right now it eludes me!
 

ipswichcycler

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Re: Bottom bracket torque
« Reply #6 on: August 14, 2014, 07:52:22 AM »
Thanks again for the replies. It's always interesting to see what other people do.

geocycle

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Re: Bottom bracket torque
« Reply #7 on: August 14, 2014, 05:39:29 PM »
If you're on the thick part of the EBB it will stand a good tightening.  It's a pretty thick lump of aluminium and protects the BB to quite some degree.  Once the chain has stretched again you will be making a fresh set of indents anyway.