Sunday, June 26, 2011

Betrayed with a Click

I've been working on bike, cars, ???, since my childhood. After a while, you develop a preeettty good feel for how tight nuts, bolts, and screws should be. However, with the advent of carbon fiber, and titanium bolts... I relied on a torque wrench for many fasteners on by bike.

About a week ago, while tightening the faceplate on the HighBall's stem, I noticed the torque seemed really, really high and no *click*. I backed off the setting, re torqued and everything seem to work fine. I reset to the proper torque and it just a touch *click*. Hmm... ok.. I'm crazy.

This weekend while relocating the shift levers on the HighBall, I again sense the torque is high, but no *click*. I proceed. *Crunch* What was that? Wassat? Nah. Couldn't be. I move to the other side and again *Crunch, pop*. I feel around the clamp, and yep. I've crunched the bar. Crap. Recheck the setting... it's correct.

When I remove the bar... the faceplate has dug in pretty good too. Failure waiting to happen.

I've used multiple click-type torques wrenches through the years with much success. Many claim they can fall out of calibration. But honestly, I've always dismissed this - if anyone designes a fastened connection that can't tolerate a 5, 10 or even 20% torque... shame on them.

But this wasn't a calibration error. It was outright tool failure -something I never contemplated. I can no longer recommend Syntace's wrench.

The old-fashioned beam type wrench can never suffer this type of failure. But, I find them really akward to use. And the Park Tool beam wrenches split the most common torque ranges -forcing one to buy and carry two wrenches, and use them at the extremes of their ranges. The higher-torque wrench not having the scale resolution for descent work, on the low end.

I compromised and bought a dial indicating wrench. Best of both worlds I hope. It's simply a deflecting beam tied to a calibrated dial indicator graduated in N-m in my case. Thus it can't really suffer the calibration or failure issues (like a beam wrench) and it's easy to read, (unlike a beam wrench).

It's worth developing a good "feel" for fastener tightness if you don't already have it. Most importantly: Trust thyself when it comes to torque wrenches.