RE: cylinder studs: torque or length?

["Minor, Bob" <Bminor@xxxxxxxx>]

What you have to realize is that a torque spec, if properly developed,
is derived by calculation to achieve a prescribed amount of stretch. The
stretch is what actually provides the clamping force through tension and
compression. If the variables you mention affect the final clamping
force to the degree that you surmise, they would affect the torque
wrench method every bit as much as the degree method.   Where the degree
method is superior with regard to achieving a more precise clamping
force, is that it is not affected by factors like lubrication and
surface finish of the parts.

"All science is Physics, everything else is just stamp collecting"      


<<I have no doubt that in The Factory the stretch method is best. And 
under ideal textbook conditions it may often make sense under the 
shadetree (or as we urban tinkerers say, "curbside").

But in practice, I ask you to count the number of joints between the 
stud nut and the engine block (Is it 5, give or take a washer?). Now 
consider the history of pulling and stretching and heating that EACH of 
your studs may differently have had - confident you know that history? 
If you switch nuts, are they all the same flatness because with the 
stretch method, every micro-millimeter counts?

Now, do you feel confident that when you tighten to a wispy specified 
torque of 15 ft-lbs, you are properly snugging-up all those joints with 
all kinds of unpredictable new and old stuff in those joints? The 
stretch method STARTS by torquing the heads to that wispy, smeary 
figure THEN it cranks in an unvarying stretch of half a thread pitch to 
a long stud of unknown prior stretching, heating, and whatever.

At the least, the torque method, used for centuries for all I know, (1) 
uses one method instead of two-in-series and (2) allowing for 
frictional issues, pretty much speaks to the heart of the issue: force 
per se.

Ben
After 40 seasons with BMW twins, still just a PhD Human Factors 
psychologist, so what would I know about real-world treatment of "soft 
data" or the cognitions of the humans at the end of the torque wrench>>

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