Stem bolts sheared on brand new bike

[Goobs]

I have just bought a Defy1 and used a new torque wrench set to 2nm to tighten the bars to the stem. The max torque says 6nm so I assumed this would be a safe setting yet the first bolt I tightened sheared off in 2 turns.

To say I'm annoyed is an understatement.

I don't know if the torque wrench is faulty or the bolt but what chance have I got of getting this sorted when I ordered the bike mail order from Rutland Cycling ?

 

[Drago]

Strewth, my money is on a dicky wrench.

 

[400bhp]

Seems very odd. Must be rubbish bolts, which has very little to do with the bike, the real parts or Rutland Cycling to be fair.

 

[compo]

What is the range of your torque wrench, ie, minimum and maximum torque settings. Most torque wrenches are not that accurate at the extremes of their range, being most accurate in the mid ranges. This applies especially to cheaper tools, but also to more expensive ones. You could do a lot worse than the pre-set torque set allen keys for bikes requiring such low torques.

 

[woohoo]

I very much doubt that this is the explanation in this case (it seems too extreme) .... but bolts should be torqued dry. The manufacturers' figures are for dry threads. If the threads are lubed then it is easy to tighten the bolts further into the recess than the spec and stretch them well before the recommended torque figure is reached and sometimes they then shear.

 

[smokeysmoo]

I've never sheared a stem bolt, both when I had a torque wrench, before I had one, or any time since, and although I trust my judgement nowadays I was never known for my mechanical sympathy

Which torque wrench is it? 2Nm wouldn't shear bolts that are designated for 5 or 6Nm unless someone had really overtightened the bolts previously.

My money is also on the tool being poorly or not at all calibrated.

 

[Goobs]

This was the wrench :
http://www.amazon.co.uk/Mighty-8802...12526086&sr=8-1&keywords=mighty+torque+wrench
I tested it by holding the end with pliers and it slipped ok so I can't understand why the bolt sheared.
They were already lubed.
Could they have been pre-stressed at the suppliers ?
They are closed today but I suspect I will have a job on getting any help from Rutland Cycling tomorrow.
If so I have half resigned myself to getting a refund on the torque wrench and buying a new stem for £25.

Nice shiny new bike sat in the garage unused on a sunny Sunday

 

[Smurfy]

A proper engineering fitting shop will always use a calibrated instrument to set the torque, rather than the scale on the torque wrench. Unfortunately such instruments are extremely expensive.

Also bear in mind that when there is more than one bolt to tighten, you should tighten them all gradually, rather than putting the specified torque on one bolt straightaway.

I don't bother with a torque wrench, except for crank bolts. I just do them all by feel, and have yet to wreck any.

 

[400bhp]

This was the wrench :
http://www.amazon.co.uk/Mighty-880275-Torque-Wrench-Black/dp/B001R4BR1O/ref=sr_1_1?ie=UTF8&qid=1412526086&sr=8-1&keywords=mighty torque wrench
I tested it by holding the end with pliers and it slipped ok so I can't understand why the bolt sheared.
They were already lubed.
Could they have been pre-stressed at the suppliers ?
They are closed today but I suspect I will have a job on getting any help from Rutland Cycling tomorrow.
If so I have half resigned myself to getting a refund on the torque wrench and buying a new stem for £25.

Nice shiny new bike sat in the garage unused on a sunny Sunday

What am I missing here?

You sheared the bolts but i) need a new stem and ii) need to contact Rutland Cycling?

 

[T.M.H.N.E.T]

Rutland cycling had nothing to do with it

 

[Goobs]

To clarify my point:

Knowing I had spent a sizeable chunk of money on a new bike I thought it a good idea to buy a torque wrench in order to hopefully tighten bolts properly without damaging them. This bike cost twice my last one so I was trying to be more cautious setting this one up. I may as well have saved the money on the torque wrench and hand tightened the stem bolts or better yet paid a LBS to check it over for me.

Lesson learned.

 

[Profpointy]

I very much doubt that this is the explanation in this case (it seems too extreme) .... but bolts should be torqued dry. The manufacturers' figures are for dry threads. If the threads are lubed then it is easy to tighten the bolts further into the recess than the spec and stretch them well before the recommended torque figure is reached and sometimes they then shear.

are you sure torque settings are for dry threads? I thought usually the opposite - particularly if they aren't going in easily as it were.
And in any case, how can you shear the bolt with a lower force than the bolt can take just because they're lubed.

 

[jiberjaber]

A proper engineering fitting shop will always use a calibrated instrument to set the torque, rather than the scale on the torque wrench. Unfortunately such instruments are extremely expensive.

Also bear in mind that when there is more than one bolt to tighten, you should tighten them all gradually, rather than putting the specified torque on one bolt straightaway.

I don't bother with a torque wrench, except for crank bolts. I just do them all by feel, and have yet to wreck any.

Or you could adapt the following process to confirm what the real torque value is for a given value on the wrench... no need for expensive calibration equipment, just a vice or similar to hold the wrench in, some scales to measure the weight and some lead to make the weight.

http://www.wikihow.com/Calibrate-a-Torque-Wrench

 

[sgl5gjr]

6nm is not really much torque at all.... as a classic car specialist I use torque wrenches and these days on low torque (not as low a 6nm) I tend to tighten by "feel"....... and even checked with a torque wrench I'm never far out.
To be fair..... you'd really have to be ham fisted to have sheared off at 6nm as that's only 4.5 ft/lb in old money. Lets be honest too...... I find that most adults can tighten a car wheel, by feel, to almost what manufacturers torque settingsare....... by hand
If you have sheared the bolts during tightening then clearly there is a manufacturer issue from a) poor design b) cheap components to save cash & maximise profit, c) poor quality materials & d) manufacturer /cycle makers not inspecting/testing components
Return to/Contact the dealer who sold it to you for refund/exchange (Rutland Cycles in this case)
Whatever....... the cycle maker should really do a recall and replace the faulty component if there are more cases than yours for this same fault.
I know my opinion could sound a little harsh and to the point, but in my game, if I have the same issue (yep I go through thousands of fixings of all types) with a part or fixing and it doesn't meet the spec..... it gets returned and I often never use that brand/supplier ever again.....I cant afford any rubbish, when customers want their vehicle to be just so

 

[woohoo]

are you sure torque settings are for dry threads? I thought usually the opposite - particularly if they aren't going in easily as it were.
And in any case, how can you shear the bolt with a lower force than the bolt can take just because they're lubed.

Yes. The advice appears in lots of places (although to be fair others say slightly different things) from the car manuals of Mercedes, Volvo, Chevrolet etc (where the figures are much higher) to other general sites such as http://jthomaseng.com/the-effects-of-lubrication-on-fastener-torque

Often times while consulting with a client on a particular truss, we are asked for its proper torque setting. Though we can provide you with a general answer for each truss that we manufacture, it is important to keep in mind that the use of a lubricant on your fastener torque can change everything.
......
The amount of torque used in the installation of any kind of truss is once again crucial to its stability. Though you may think that you know the proper torque settings for your project, it is imperative that you make necessary adjustments if you plan to use a lubricant to make bolt tightening easier.

which should answer your second point i.e. the lower friction allows the bolt to go in further for a given force which stretches (and eventually narrows) the bolt which causes it to break.