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Installed some new suspension pivot bearings at the weekend and went to finish off last night by tightening the pivot bolts to the correct torque after buying an 8mm hex adapter. I bought a torque wrench about 5 years ago and have used it, I guess twice in that time, both times for suspension pivots. I set the wrench correctly to 300 in/lbs as indicated on the bolts but the wrench didn't 'break away' at the point I expected it too. I had to undo the bolts which were very tight and hand tightened to what I would use to tighten square taper crank bolts.
So - Whats wrong with my torque wrench, does it not like only being used once in a blue moon? Did I buy a cheap wrench that's not up to it (Draper - £28.99)?
Thinking I should just stick to feel rather than using a torque wrench anyway if it's not going to be reliable, afterall that's what I do on every other bolt and I've never had a problem with over-tightening or stuff coming loose.
Did you wind it off before putting it away last time?
We've had it at work where a wrench has been left set at 20ftlb for about 12 months.
It was no where near when we came to use it again (compared to a new/calibrated one).
300in/lbs is pretty tight, so I think I'd want a properly calibrated torque wrench for that...
[i]
3. Torque wrench storage. Don’t get lazy!
digital torque wrench. A torque wrench in regular use doesn’t need to be wound back. If you expect to store a torque wrench for more than a few weeks, always wind it down to the lowest scale setting (never to zero).
Storing a fully loaded torque wrench can result in a set in the spring, weakening the spring over time. But if you completely offload the spring to the zero setting, other components within the wrench may move a little. And in the world of torque, a little is a lot. Reapplying spring compression will shift orientation of these components, affecting accuracy[/i]
Yes I think you always have to apply a bit of common sense with torque settings.
I have encountered stems with 12-13Nm spec on M5 bolts, which just seemed too much when tightening them so I think I settled on 10 or so. Most M5 bolts seem to be 4-8Nm (obviously these might have been a stronger material etc., but I could feel that the torque just wasn't ramping up - the point where if doing it up by hand you would definitely just stop.)
Yeah I wound it off, although it was wound off all the way as I think that's what the manual stated.
To be pedantic,in/lb would be inches per pound, which is not a unit of torque.
My torque wrenches might be now so reliable either...
But following procedure works:
lets say the torque I should go to is 15 Nm
I put the wrench onto the lowest setting (example 5 Nm) and let it "break away".
After this the "15 Nm" will work also...
If I don't do this strange procedure the wrench is sometimes "stuck". Also always unwinding the thing before I put the wrench back.
Above: a "friction" thing? Wrench has to come alive first...?