Never using an adjustable torque wrench again!

[Manc33]

I set my Cyclo Torque Wrench to 12Nm for the HT2 crank bolts and tightened each both alternately as you do, all of a sudden I felt it go loose. The torque wrench had sheared a bolt clean in two. The bolts are supposed to be 12Nm-14Nm so, I was supposedly being cautious. God knows what this thing was really tightening them to. Could have been 18Nm or 20Nm for all I know.

Now I have got to mess about buying a 3mm carbide drill bit to drill out the piece left in the crank arm.

I wouldn't mind but I paid £40 for my torque wrench and that same one is now over £50. Terrible.

I think ones like those Ritchey that are set to 5Nm and only 5Nm, are probably legitimately tightening to 5Nm, but these adjustable torque wrenches are just carp.

Ages ago when I got it I was reading about ones like Park Tool and a lot of people said even those, at the price they are, aren't actually reliable. I doubt any are, not at these "low" torques. Apparently the lower the torque, the more likely it's wrong. You can get these wrenches calibrated and mine did come with a certificate to say it was calibrated. I wouldn't even sell it to someone.

This is also the same torque wrench that (at 5Nm) crumpled a carbon seatpost. Luckily it was a cheap one from China, but then that might really be why it crumpled, I will never truly know. With it being this torque wrench it could have been 8Nm or 10Nm for all I know.

We think we are being careful using these things, but the opposite is true, or has been in my case.

Back in it's case it goes and I am never using it again.

[tim-b]

Hi
Get its calibration checked. If you have a friendly engineer, mechanic, etc then they will have arrangements for calibration and at around £12 (add the same again for an adjustment) as part of a bigger job it's not too expensive. The service that I piggy-back is mobile because they do the vehicle lifts, trolley jacks, etc, so no postage or travelling required.
Always set the torque wrench and click the torque off against a static load (I clamp a suitable socket in the bench vice) a couple of times before using it on the real fastener; mechanical wrenches often start high until the mechanism has settled
Regards
tim-b

[The utility cyclist]

Maybe you could contact local trading standards and see what they have to say, save you the expense of having an independant firm do it. Very likely it won't just be yours that is out. In any case you should contact the company and ask for recompense for the tool and the cost of replacing cranks or at least extracting the bolt.
Personally I've never trusted to them though have a draper, even on my carbon bits I'd rather go by hand/feel.

[Greystoke]

A good rule of thumb is to use a spanner. Smaller size spanners have shorter shafts for that reason....so you can't over tighten. Use these.

[mjr]

My Topeak and Draper beam torque wrenches seem accurate. My clicking wrench failed fairly quickly, but the other way, too low.

[Brucey]

you can read some of my thoughts on clicky torque wrenches here

https://forum.cyclinguk.org/viewtopic.php?f=5&t=124576&p=1269721&hilit=torque#p1269721

- including that I agree with tim-b's comment above about them overtorquing if they have not been used for a while.

Worse yet there are some that can be permanently damaged just by backing off the adjuster fully; if you can turn the adjuster past zero (to a 'negative' setting) then parts of the mechanism can come adrift inside and the wrench will never work properly again unless it is disassembled and the reassembled correctly again.

Since they go out of calibration quite easily, and it is easy enough to check the calibration on a torque wrench, I'd suggest that anyone who owns and uses such a thing gets in the habit of checking the calibration on a regular basis.

cheers

[Bez]

Hmm. Have you eliminated the possibility of a material flaw in the bolt? Seems an unusual failure: I'd normally expect overtorquing to first cause damage to either the head or the thread in the crank arm.

[Mick F]

I've only used a Torque Wrench when tightening cylinder head bolts.
Get them tight of course, but the main thing was to get them all at the same tightness.

Other than that, never needed or used one as I don't fix engines any more.
The one I have hasn't been used in years and years - maybe last century.

[Cugel]

Perhaps the bolt is at fault? Some have flaws in their structure, producing a weakness that can lead to an easy snap. If it's been in and out of the threads a few times, it can be weakened.

To remove a broken bolt from such a crank it's far better to use a hacksaw blade or similar rough-edged thin thing. Place it in the gap of the crank so it's teeth rub against the threads of the broken bolt-bit. This will rotate the bolt as you push the blade across the threads, unscrewing it from the threaded hole.

You need to put the right pressure on the bolt threads with the blade, to allow the bolt-bit to turn. Too much pressure and it binds; too little and the blade just slips over the threads.

If the bolt broke below the crank-arm gap, inside the threaded bit, this will not be possible. However, using a drill bit to drill out the broken bolt is likely to lead to bit-slip and damaged threads in the crank arm bolt hole. How do I know these things? Yes, you guessed!

Cugel

[Brucey]

BTW HT-II crank bolts are a bit like stem bolts; they may well see low-cycle fatigue in bending as they are installed, and may thus be prone to breakage if they are repeatedly tightened. Another thing that will help them to fail in this way is if the spline itself is slightly worn; this will be more likely to set the bolts into a slight curve and this will tend to break them more easily.

I would recommend that you replace these bolts if (say) they are re-used more than a few times in a good crank, and if the spline is worn, consider replacing them every time the crank is reinstalled.

FWIW removal of the broken bolt ought to be fairly straightforward in this case, since you have access to both ends of the bolt. An easy-out ought to do it.

cheers

[rmurphy195]

Hmm. Have you eliminated the possibility of a material flaw in the bolt? Seems an unusual failure: I'd normally expect overtorquing to first cause damage to either the head or the thread in the crank arm.

Quite agree - whenever I've overtightened a bolt its always been the thread that's stripped, especially into alloy.Sheared bolts have always happened when undoing them - or in one case, when a garage re-used a bolt instead of replacing it (on part of the suspension!) ... results were"interesting".

[alexnharvey]

I set my Cyclo Torque Wrench to 12Nm for the HT2 crank bolts and tightened each both alternately as you do, all of a sudden I felt it go loose. The torque wrench had sheared a bolt clean in two. The bolts are supposed to be 12Nm-14Nm so, I was supposedly being cautious. God knows what this thing was really tightening them to. Could have been 18Nm or 20Nm for all I know.

Now I have got to mess about buying a 3mm carbide drill bit to drill out the piece left in the crank arm.

You could use either a left hand drill or a damaged screw extractor to try to screw it out. I haven't had to use them on a bike yet but I've been very impressed with screw extractors.

[iow]

I assume the torque spec' varies with how/if the thread has been lubed (dry, oil, grease, anti-seize etc..) is a c. 20% tolerance enough to cover this?

[Bez]

Quite agree - whenever I've overtightened a bolt its always been the thread that's stripped, especially into alloy.

For additional context I should add that HT2 bolts were the only time I've ever felt a need to use (and thus buy) a torque wrench. I couldn't stop the damn cranks creaking (and I tried multiple sets) so figured my normally adequate "torque instinct" was off the mark. Turns out it wasn't at all, but it did inform me that on these bolts the recommended torque was at a level where the bolt heads were just starting to deform (your allen keys may vary). And, as above, stripping an alloy thread seems more likely than shearing a (flawless) steel bolt.

(FWIW I never solved my HT2 creaking problem; eventually I switched to GXP cranks and they've been just dandy ever since.)

[horizon]

There's a thread somewhere about not using a torque wrench at all and going just by feel. If anyone can find it I would be very grateful!