As I posted yesterday I had to install a new BB in my touring bike. I've posted many times before about using a torque wrench to properly afix crank arms. Instead of repeating here's a url to an old posting about my technique: tinyurl.com2cyvhOpen ↗
Anyway, I got to thinking about the proper way to use the wrench. It occurred to me (after years of doing this) that applying the torque against the arm being afixed involves some side loads in the arm/ taper interface. As an experiment I torqued the arms the way I usually do, then retorqued against resistance applied to the opposite arm. Guess what, the bolt turned a bit before again reaching 30 ft.lbs.
I'm not sure what this all means, but I'll be using this technique from now on. Of course this all means nothing to the "calibrated forearm" crowd. ;-)
As I posted yesterday I had to install a new BB in my touring bike. I've posted many times before about using a torque wrench to properly afix crank arms. Instead of repeating here's a url to an old posting about my technique: tinyurl.com2cyvhOpen ↗
Anyway, I got to thinking about the proper way to use the wrench. It occurred to me (after years of doing this) that applying the torque against the arm being afixed involves some side loads in the arm/ taper interface. As an experiment I torqued the arms the way I usually do, then retorqued against resistance applied to the opposite arm. Guess what, the bolt turned a bit before again reaching 30 ft.lbs.
I'm not sure what this all means, but I'll be using this technique from now on. Of course this all means nothing to the "calibrated forearm" crowd. ;-)
any time you "retorque" a fastener, it will get tighter. Once you've set the torque wrench to the final torque, don't "retorque"; all you are doing is making it tighter than specs. If you don't believe me, go out to your car and torque a lug nut to specs. Then reposition the torque wrench so that you can crank it down again. You'll see the torque wrench handle move before it clicks, as often as not, indicating that you've moved (tightened) the lug nut. This effect doesn't occur EVERY time you "retorque" but it WILL occur on some fasteners.
As an experiment I torqued the arms the way I usually do, then retorqued against resistance applied to the opposite arm. Guess what, the bolt turned a bit before again reaching 30 ft.lbs.
It's likely that it would have done so with a retorque done identically to the first. If you have a junker bike around, try it and see. -- Typoes are a feature, not a bug. Some gardening required to reply via email. Surrealism is a pectinated ranzel.
any time you "retorque" a fastener, it will get tighter. Once you've set the torque wrench to the final torque, don't "retorque"; all you are doing is making it tighter than specs. If you don't believe me, go out to your car and torque a lug nut to specs. Then reposition the torque wrench so that you can crank it down again. You'll see the torque wrench handle move before it clicks, as often as not, indicating that you've moved (tightened) the lug nut. This effect doesn't occur EVERY time you "retorque" but it WILL occur on some fasteners.
If the fastener is driving something onto a tapered hub, this is a reasonably accurate observation. For fasteners in normal applications, a retorque should produce little or no motion. As has been pointed out multiple times, however, cranks tend to "creep up" the taper, causing the fastener to lose apparent tension. Mostly, this is reported with regard to bolts seeming loose after just one or two rides follwoing installation, but in my experience, the amount of creep that accurs within a few seconds of removal of the wrench can be enough to make the fastener appear to have been incorrectly torqued by a significant margin. -- Typoes are a feature, not a bug. Some gardening required to reply via email. Surrealism is a pectinated ranzel.
applications, a retorque should produce little or no motion. As has been pointed out multiple times, however, cranks tend to "creep up" the taper, causing the fastener to lose apparent tension. Mostly, this is reported with regard to bolts seeming loose after just one or two rides follwoing installation, but in my experience, the amount of creep that accurs within a few seconds of removal of the wrench can be enough to make the fastener appear to have been incorrectly torqued by a significant margin.
Don't you have to at least load the cranks to have creep occur?
applications, a retorque should produce little or no motion. As has been pointed out multiple times, however, cranks tend to "creep up" the taper, causing the fastener to lose apparent tension. Mostly, this is reported with regard to bolts seeming loose after just one or two rides follwoing installation, but in my experience, the amount of creep that accurs within a few seconds of removal of the wrench can be enough to make the fastener appear to have been incorrectly torqued by a significant margin.
Don't you have to at least load the cranks to have creep occur?
Not in my experience, though loading them will greatly increase the creep. I intentionally retorqued the same left crank six times, waiting 15 minutes between each attempt, and got a surprising amount of rotation each time. This was with a Snap-On click-type wrench that was left at the same adjustment point throughout the test. -- Typoes are a feature, not a bug. Some gardening required to reply via email. Surrealism is a pectinated ranzel.
