"Doc" > wrote in message
ups.com...
> Just pondering the 9 ft/lbs specified for the rear seal housing on
> my
> Cressida per the factory manual. How are bolt torque numbers
> determined?

This is a very complicated issue. In general the engineers would
determine a target clamping force and work backwards from there to
determine a tightening torque. For a gasketed joint, they would
determine a bolt pattern and pick a bolt size to provide the required
clamping force (and consider the mechanical strength for a load
carrying member). The bolts would be sized so that when properly
torqued they would be at something like 80% of their proof load. The
torque needed to achieve this clamping force is a function of the
materials involved (bolt material and base material for female
threads), plating (these affect the frictional characteristics of the
joint as the bolt is torqued), lubrication (another contributor to
frictional characteristics), head style, etc. The type of loads the
bolt would be subjected to would also be important (axial, shear,
combination, static, varying, etc.) For a joints subjected to varying
axial loads, they would go for a higher percentage of the proof load
(90 to 100%). Most modern head, rod, and main bearing cap bolts are
torqued to the yield point. This is done using specialized machines
that sense a change in the stress strain relationship as the bolt
reaches the yield point. This is a very good way to torque bolts for
variable loads, but difficult to duplicate in a repair environment.

I have some information of torque settings at
http://home.mindspring.com/~ed_white/id9.html , but it is simple
information related to steel on steel joints with non-reversed
stresses.

Ed