Torque ratings are just a way to specify bolt stretch, it's the streching of the bolt that maintains the clamping force. Believe it or not steel, like most metals is elastic. Many professioal engine builders measure bolt strech rather than torque when assembling motors (on things like rod bolts where you can get to both ends of a bolt).
When you torque a bolt is is possible to strech the bolt past it's yield point (by overtorqueing) the tensional strength of the bolt decreases, up to the point where the bolt breaks.
In the automotive world it used to be common practice to retorque head bolts after running the motor for a few hours (or driving it awhile), improvements in head gasket construction have pretty much eliminated this requirement.
A "good" engine builder will measure the studs (or bolt) length before reusing them to determine if they have been streched past their yield point by someone in the past. If you don't know the original length specification, then either you install them with no idea if they are going to fail, or use new ones.
If it's your bike you are working on it's no big deal, if it breaks then you fix it. If it's a customers bike and it breaks, then the customer tells everyone that you do shoddy work and your reputation take a nosedive.
KD9JUR
