Originally Posted by N20jeep
Yes; per manufacturer literature, fastener industrial documentation, and experimentation.
Recall that the purpose of "torquing" a screw isn't putting a specific torque
(turning force) load on it, it's to put a specific tensile
(stretching) load on it. Measurement of the force needed to turn the screw is an indirect mean of measuring that tensile loading.
There's a very good reason that performance aftermarket connecting rod bolts and nuts don't come with a torque specification - they come with a stretch
specification. And you can get a "rod bolt stretch gage" - it's set to zero with a resting bolt, you put a box wrench on the hex, and you turn the nut until you get that specified stretch value.
Direct measurement of bolt stretch is the most reliable means of establishing and measuring tensile preload, since yo're measuring it directly.
The torque (turning force) required to attain a certain tensile load will decresae as the threads are lubricated
relative to the "clean, dry" specification given in the manual. The amount that the applied turning force is to be reduced is determined by the lubricity of the applied compound - starting with threadlocker compounds at "0% adjustment" (they're not lubricants, and they're formulated to not
change the Cf between the thread surfaces.)
Yes, cleaning and lubricating the threads will also allow for more consistent application of tensile preload, but that is not the only effect.
Conversely, if you do not
clean the screw threads or the holes, you'll end up applying less
tensile preload to the screw/bolt shank for the same "clean, dry" torque value - because the friction between the thread surfaces is greater. There's no set definition for how much of what will reduce the tensile loading by how far, but it's not a situation where the values would need to be known anyhow (use a wire wheel to clean your screws if you have to, and making a set of thread chasers in the shop is a simple process with a Dremel or other thin cut-off wheel, a high-speed spindle, and a set of hardened screws. Cut three or four flutes longwise across the threads of the screw, and back it out to clean the flutes out every 2-3 turns to remove accumulated crud. You use screws so you can't cut new threads and screw up the hole, but you can purchase purpose-built thread chasers. But why? They're cheap and easy to make in the shop.)
Rumour has it that newer never-seez compounds are formulated to prevent seizure and to not
lubricate the threads in so doing, but I will believe that when I can turn up information from the manufacturers. The last manufacturer information I have is to reduce "clean, dry" torque by half
- this from two or three different reliable manfuacturers (one is Permatex/LocTite, the other two were sold to me by MRO houses.)
As far as "high-load" torque wrenches, I think the highest I'd seen was a 1' drive job that went up to 500 pound-feet...