Hey are the factory head bolts the "torque to yield" variety?
I say cheap insurance in any event to spring for new head bolts.
Every fastner is designed to stretch. This is what provides the clamping force which retains the bolt, nut, etc. Or rather they are designed to act like a spring. The proper term for this characteristic is reffered to modulous of elasticity (help me out here anybody into mechanical engineering) which refers if I remeber correctly to the elastic and plastic properties of a material. When you torque down a bolt (and it is correctly done) the bolt is stretched out and provides the proper clamping force while still remaining in the elastic state allowing the bolt to return to its original state when removed. If the bolt is over-torqued (or possibly fatigued through shock, thermal cycling, abuse, etc.) then it stretches to the point where it enters the range of plastic deformation and results in a loss of its mechanical properties and niether does it return to its original state. Causing a loss of clamping force.
Better yet think about this when the local tire gorrilla hammers down on your pride and joy with an impact wrench, to "keep the nuts on tight" stretching them out in the process.
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