How do I set Allen Key Bolts to specific nM settings?

[Taff]

Hi all,

Sometime back I started a thread on my Neo Cross not making any difference whatever the setting. I e-mailed NH agent and got this reply:

With regards to your issues I can only suggest that your torque sensor is misreading, there are 5 allen key bolts on the rear right subframe where the axel bolts for the rear wheel locate on the frame when standing behind the bike. There are 3 M6 OR 7 allen key bolts these need to be loosened off then retightened to 10nm and the 2 smaller m3 allen key bolts need to be loosened then retightened to 1nm.
Herewith torque sensor adjustment. (Below)

Now as useless and clumsy as I am I THINK I could do this if I knew how and had correct equipment. Obviously I need something to measure the torque?
(Hark at me sounding like I have a clue lol)

Please advise anyone.

Taff

 

[neptune]

The correct equipment to do the job would be a torque wrench. These are usually designed to fit half inch drive sockets, you would then need an adapter and some straight allen key bits. A torque of 10nm means a ten Kilogram force on the end of a one metre long lever.
Here is a cheap way to achieve the same result. Cut a piece of tubing to half a metre long, and fit it over the handle of your allen key. Then you need a spring "balance" of the type used to weigh fish. You then connect it to the end of your lever and measure the tightening force you are applying. 20 Kg at half a metre is the same force as 10 KG at one metre, or 40Kg at one quarter of a metre.

 

[Scimitar]

10NM is equal to 7.3 ft/lbs - you put ten kg on a metre long bar and watch the threads strip out.
http://www.convertunits.com/from/newton+meters/to/foot+pounds

 

[neptune]

@Scimitar. I bow to your expertise on this. The same principle applies as regards equipment however. I can not quite understand how I got it wrong. My understanding is this 10NM is ten newton Metres. One Newton is the same as a Killogram except it describes force rather than weight. Please explain how I got it so wrong.

 

[Scimitar]

There you go...
FACOM - Torque Control
The relationship isn't straightforward and it's been decades since I did physics (so long, in fact that Nm were only a new-fangled way of doing things back then) and I've always double-checked in Imperial measures since that's what was ingrained in my psyche early on. My initial gut-feeling and knowledge of a 6mm bolt into aluminium alloy is that you cannot exceed 18 to 20 lb/ft on those and that's for tightening down properly - witness the amount of stripped M6 bolts on motorcycle engines for example, installed by ham-fisted goons. So, knowing that 10Nm was ringing alarm bells I went and looked it up - and found, to my relief that I wasn't wrong. As you can see from that page, the actual Kgf per m is 0.102 if you were to do it with a weighted bar - which is about right; that would be in the ballpark of the right weight at the right distance for a simple weighted bar.
Your method of the weighted bar *does* work; I've used it from time to time in Imperial applications, like hub nuts, etc, when I've not had a large enough torque wrench available.

 

[neptune]

@Scimitar. Thanks for enlightening me on that one. I had sort of assumed that a newton and a Kg were much the same thing. So in round figures, for this purpose I NM is about one tenth of a Kilogram metre. I have use the weighted bar method on nuts that were only accessible with an open ended spanner, so a socket could not be used.
Perhaps the best advice would be to borrow the correct tools.

 

[bilabonic]

Parktool do a bike torque wrench.

Handy when you have a lot od carbon fibre gear.

 

[oigoi]

1 newton is near as dammit 100 grams or 0.1kg so 1nM is a force of 100 grams exerted at a distance 1m from the centre of the bolt and 10nm is a force of 1kg exerted 1m from the bolt.

 

[amigafan2003]

Meh, real mean use proper measurements.

One white knuckle
Two white knuckle.
........
Nnnngh that's bloody tight

And finally

4 bloody knuckles, someone pass me the lump hammer.

 

[jackhandy]

Best description I've seen of how to assess correct torque/tightness for crank bolts...

Tighten to a grunt - not a fart.