So, how do the factories send out millions of vehicles that run hundreds of thousands of miles without retorquing?
Umm, why do you think the first required warranty service has to be done in just a few hundred miles?
>>>*This is actually a very good question. The fact is that modern engine designs don't really require retorquing when delivered new.
The reason is all of the surfaces are correct and mated, the fastner loads are uniform and sequential and machinery eliminates the human element. The factory idea of "torque to yield" type bolts was to address the problem of premature failure, also.
When replacing a head gasket, we are often putting a freshly surfaced head on a block that has been through many heat cycles. Now there are imperfections in the surface.
Plus not all resurface jobs are equal, the microinch or roughness of the finish is important. In the aftermarket, this can vary somewhat depending on the equipment used.
Few shops own an infinitely variable speed milling machine, I happen to own one and I don't know of another shop in our local area that does. Some aluminum heads require 3600 cut per inch/minute to be correct.
That is a bit smoother than a freshly buttered newborn baby's bottom....*LOL**...
We suggest retorque anyway. As the O/P noted, it can matter because circular torque and clamping force are not the same thing. One simply relates to the other mathematically.
Any friction at the threads will cause a higher torque reading and lower than desired clamping force.
Clamping force is what keeps the gasket intact and sealed, after a few heat cycles, that shows up.....*EB
