<For the metric impaired, "20 Nm"? Ft/lbs..Inch/lbs value?>

20 Nm = 177.015 lbf-in (14.751 lbf-ft)

http://joshmadison.net/software/convert/download.php

will give you a free download that will convert just about anything to just about anything.



<Seems as though the torque wrench error would be the LCD.>

Correct - it's just that 10% error of 20 Nm is less than 10% of 45 Nm, and since 20 Nm is easier to measure, the percentage itself might be smaller. Using the wrench for the first 20 Nm gets you to a reasonable starting point, and the torque-angle method introduces less error for the final steps, so the overall result has less error.

Still - check those threads for damage, clean them, and put a light lubricant on them so they all need about the same amount of turning force. Bring them all up to 20 Nm evenly, it might take several trips around the pattern.

Hey Anotheroldrider!

Thanx for the conversion dealie.

Thats neat..


Corky

When you think about it, neither method of re-torquing a used gasket in a working oily engine that's been torqued and stretched a couple of times before makes trustworthy sense. It works in practice only because there's a big gap between (1) tight enough for a well-designed gasket to be leakproof but (2) not stripping the aluminum threads.

For me, far smaller pile of untestable assumptions needed using the old torque wrench method.

If you use the stretch method, I'd say don't take your eyes off the torque wrench so it doesn't go over say 45 ft lbs, whatever the number of degrees of rotation.

> Correct - it's just that 10% error of 20 Nm is less than 10% of 45 Nm, and since 20 Nm is easier to measure, the percentage itself might be smaller.

Very true, and well explained, but the benefit goes well beyond that. Basically, at low loads, surface imperfections, dirt, and other forms of unwanted additional friction, play a smaller role (just do a little gedanken-experiment and picture rubbing your hand across a grabby surface like coarse sandpaper with a light brush vs a very large downward pressure -- big difference, no.
Now picture dragging your hand either lightly or heavily across a wet soapy piece of plastic or other smooth surface. Sure, there's still a difference between the friction you feel at on a grabby and a smooth surface, but that difference is less at light lpressures. We take advantage of that, and what anotheroldrider described to minimize errors in both the torque wrench and the variance in the surface friction (which causes large variances in torque results) , to get a fairly accurate baseline. Then apply the very accurate incremental torquing on top of it. Best we can do without strain gauges, or calibrated plastic or elastic deformation.

Excellent discussion...this surely is a great Blog for OilHead/HexHead owners who like to wrench!