Proper Tensioning Of Fasteners

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Proper Tensioning Of Fasteners
- by Pete Snidal (C)2001 I remember the torquewrench thread - we exhausted that on pretty well! I think I can summarize:
The main thing you need to master in tightening things down is "feel," and with or without a torquewrench, it takes some experience. You need to be aware of the three stages of tightening any fastener:

1) The "snugging" as the two parts being bolted together come together. - Wrench moves fairly easily.
2) The Actual tightening as the fastener no longer moves the parts, but the threads are tightened against one another to prevent loosening - although you're increasing the pressure on the bar, the wrench moves hardly at all
3) The "stretch" as the bolt or stud is actually stretched from tightening. You want to stop just as this point is reached, and you _certainly_ don't want to exceed the "Elastic Limit" - the point of stretch at which the fastener will not return to its original size when the tension is removed. - this is where, as the pressure on the bar is increased, the wrench starts to move again. Not a Good Thing! (TM)
You can "feel" these stages with any kind of bar or wrench (or spanner), whether or not it's got a scale on it, but it's handy to have a scale to help you decide what you're feeling. Once you have the "feel," you find yourself second-guessing the torque wrench anyway, but I think they're a good thing for the tyro, or the occasional mechanic who may forget in between rebuilds, and I use one most of the time, especially when I have the torque specs for the thing I'm working on. (When not, I use the specs I have for similar bolts - Chevy Rods and Ford Rods are still just #10 capscrews)
The main thing to remember is to tighten things down evenly, in at least 3 stages, by the second time around (across and across, actually) you should be at the "snugging" portion of the movie, and the third time will be the tightening to just below the 'stretch." (You can feel the "stretch" portion" - that's when it starts to move again - definitely the time to stop!
The movement at the "stretch" stage may also be due to the threads coming off, or the aluminum head beginning to distort. It's a bit of a tricky stage, and I personally avoid it. If I accidentally get there, I usually back off a bit and tighten back up to just below it. It's worked for me for the past close to 50 years of monkey-wrenching!
These are the basics. Your mileage may vary.