Nice post! I have always used the technique of torquing in stages as it always made sense to do this on wheels.As an aside... I had an interesting conversation with a good friend of mine a couple of weeks ago. He was a measurements/calibration engineer for a major aircraft company until he retired a couple of years ago.
We got off on the subject of torque (as in wrenches, not engine power) and were talking about torque multipliers and systems (which he has a patent floating around out there somewhere on) and he was basically saying that all torque is basically at best a "guesstimate" because of factors that we introduce to the system when tightening up a threaded item.
When you put anti-seize on it, you mess up the torque spec. When you clean and oil it, you are messing with the torque spec. when you leave rust or other debris in place, you are messing with the torque spec.
Also, he said that the spring type "clicker" wrenches are the absolute worst, because they pop when they go over, but even when calibrated, the person using them has to use them absolutely correctly, or else they are just fooling themselves.
Needless to say, it was an interesting conversation.
1. Generally, torque is going to be a "get close" thing. You are aiming for reproducability, and 1 or 2 ft/lbs is not going to be critical because the monkey turning the wrench is the limiting factor in it.
2. Make sure that the threads are clean, lubed LIGHTLY, and free of nicks, kinks, or damage. A buggered thread will fail a torque test up.
3, Always try to turn all fasteners, nuts or whatever the same way when you torque them. That goes back to the first point above. You want to be the same no matter what.
4. Always come up to torque. Don't crank it to full torque on the first pass. Always start out about halfway to where ever you are going, then back off, reset, and snug it a little tighter, then hit it the last time. If you are torquing a wheel or a head, this is VITAL. If you don't torque them slowly up, you will put warpage into what you are torquing down, and that warpage will move around when you heat or cool the system, and also when you put it into a load situation... that's part of why tire places put the disclaimer to retorque after XX miles...
5. On any multi-fastener system (like a wheel, head etc) always alternate around the system when tightening down. This may be a 'DUH' thing to most of us, but you would be surprised how many "smart" people want to speed up the process when they are trying to get something back together... especially wheels. Take the time to snug all, then tighten all, then torque all... that's how you keep brake warpage down (Ford Taurus owner, boy can I tell you about brake warpage) Heads have a pattern, follow it. Heck, I even do it when I am tightening up exhaust flanges, water pumps, everything... anything that can be crossed around, gets the treatment. It just makes sense, especially when considering (4) above.
FWIW, I'll say that that specification looks like it was written for N/m first and then crossed over to English measure. A spark plug should be fine anywhere in that range. I never use a torque wrench on my plugs, but I've never stripped one out, either. Go to snug, then to tight, and know by the feel how good your seal is. Sorry, old school.
Thanks... missed that... and that is important, too.thank you for that excellent post
let me add one important point to your excellent and nearly complete list of caviats:
soft metals and hard metals
aluminum and brass are soft -- you really have to be careful with fasteners made of or into these metals
iron is pretty hard (your brake rotor is iron because it has excellent heat conduction)
steel is very hard.