Originally Posted by
layedback1
MECHBGON
The expert that uses the right tools and the torque wrench in question will see to it that everything is right. He will not torque a rusty or damaged bolt and call it right. A job done right according to specs by the engineers that designed and tested the product WILL work.
Wrong. To cite a couple specific examples...
1) I was building some new aluminum Treks and looked up the official torque spec for the clamp-on front derailleurs. 44-60 inch-pounds. Sounds good. I lubed the bolt, set the torque wrench for 55 inch-pounds, and began torquing. Wrench vertical, slow & easy... textbook technique. I tightened, and tightened, and tightened, and tightened. And finally overrode the torque spec, because one of three things was about to happen: the bolt would break, or the clamp would snap, or the frame would begin to crimp. This is Shimano, they're not exactly lightweights in the engineering department.
2) we built a Madone 6-series for a guy. Seatmast cap would not stay up, it kept sliding down. It was torqued correctly to max from the get-go. We had to solve that one using FSA carbon-assembly "grit paste." Nice engineering job, Trek. Oh, and it was all for naught, since the highly-engineered frame started cracking before much longer. Wheee.
3) Another Madone 6-series was built for the guy who eventually bought the shop. Wooohoo, Bontrager XXX-Lite carbon stem on carbon steer tube. Torque it precisely to 5.2 Nm (the "max" value printed on the stem). He takes it out and what do you know, the stem swivels on the steer tube. And this is high-end stuff all made (or at least marketed) by one company. The brilliant engineers at Bontrager included an anti-collapse spacer in the stem's slot, and it's too thick. It prevents the stem from getting secure grip on the steer tube. That one's my bad, I should've done a vigorous twist-the-bars-while-holding-the-front-wheel-between-the-knees check, but it illustrates the point: if bike companies made aircraft, I'd be scared to get onboard.
I'm not sure what your own background is, but I've been an LBS mechanic since '89 and worked on bikes for much longer than that, and the empirical evidence does not support your "the spec is always right" ideals. Sorry. By all means use your torque wrench, but don't let it be a substitute for prudence and common sense.
