Velomaxx said:I've seen references to torque values for fasteners that say something like 60 nm, 60 degrees.
Anyone care to say what the 60 degrees means?
Sorry Bob bur you're slighly off here.RFWILSON said:The big end con rod bolts in my old K100 are spec'd like this. They are special bolts that are INTENDED to stretch when tightening.
First you tighten them to a specified torque to get everything properly seated and preloaded, then you tighten the bolt XX degrees (and EXACTLY XX degrees!!) more to stretch the bolt an exact amount.
The reason for specifying the last stage in degrees, is that once a bolt begins to stretch, the torque actually drops slightly; it does not keep rising as you tighten. Therefore it is impossible to specify the end tightness as a torque, because it stays the same or even drops slightly in the last stages of turning.
Actually, this is exactly what happens when a normal bolt is overtightened, which is something many people are familiar with. When the bolt starts stretching, it immediately doesn't "feel" right, because you are turning it yet the force stays the same.
I'm not "off" at all. The BMW factory specification for tightening the big end bolts in a K100 (for example), states SPECIFICALLY that the bolts in question can only be used once, because they are designed to stretch PERMINENTLY when tightening. This specification also SPECIFICALLY states that it is necessary to tighten to a specified torque, AND THEN to tighten EXACTLY a specified number degrees further.Stephejl said:1. It isn't important to get it exactly xx degrees. Important torques are never given in degrees. The place you'll see that spec given most often is in structural steel and they usually give it in flats, i.e., 1/6 of a turn. It is an approximation and stretches the bolt differnt ammounts depending on how long it is. I don't like to use this spec and will generally calculate a torque to replace it. It's only advantage is that it doesn't depend on the condition of the threads to achieve correct tension in the bolt.
2. ALL bolts stretch, not just special bolts. That's why you torque them. Stretch, called preload, is what keeps bolts from backing out.
3. Torque goes up lineraly with stretch unless you reach the plastic region, i.e, past yield point. That will not happen on any motorcycle bolt. I've heard of aircraft parts spec'd this way but have never seen it myself. So your 3rd paragraph above it totally incorrect.
My advice is to always clean and lubricate your bolts well and use the torque wrench.
That is a real nice angle gauge. Is it available on the net?voxmagna said:I had a diesel cage some years back. That was when I first came across the degree angle thing and bought the gizmo that fits my torque wrench. Angular tightening was specified for cylinder head bolts. Here's a photo: