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Power Strokes
6.0 Aftermarket
Blown head gaskets with ARP's
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[QUOTE="TooMuch03, post: 969315, member: 5993"] I am not sure what you are trying to say in this post,but using big words is a good way to keep people from disputing your point. The elastic modulus (aka modulus or elasticity, aka Young's modulus) is a material property of the alloy used in the stud. It describes the relationship between stress (tensile force per cross-sectional area) and the strain (deflection per length) in the materials region if elastic deformation, and is not something you can exceed or change by over or under torquing the stud. This is a fact. The manufacturer provides a torque value that they feel will safely load the stud to their chosen stress value, typically 60-70% of the yield stress (the stress value at which the material ceases elastic deformation and begins plastic deformation). The important thing to realize here is that the stud does not have to reach it's yield stress for your headgaskets to leak. It only needs to exceed the preloaded stress that was established during the installation. If it never reaches that stress, the stud will not deform, and heat cycles and fatigue will have virtually no impact. If it does, the stud will deform, the head gasket will leak. Then, once the load is removed, the stud will return to it's previous length and the beauty of mls gaskets is that they will reseal. If you somehow reach the yield stress of your studs you have serious issues. I do have to agree with the point about over-torquing studs. People seem to think that if the studs hold at a certain torque value then they will hold all the better at higher torque values. Or, they think that because a stud gets torqued less that it has less "clamping force". By over torquing a stud all you do is increase the preloaded stress on the stud and move it closer to its yield stress. The manufacturer specifies a given torque value based on rotational capacity testing to determine what torque value will give you approximately the stress that they want(with a factor of safety for variance in torque wrenches). The testing is done under a specific set of conditions that they try to have the customer replicate, hence why they recommend or provide a certain lubricant. Unfortunately, torque is one of the least accurate ways to estimate the actual tensile force that is being applied to the fastener. Things like strain gauges and load indicating washers are far more accurate, just not something the average mechanic is willing to deal with. A whole other issue that has not yet been discussed is that the vast majority of headgaskets fail in between the studs and not at the studs themselves. This leads me to believe that heads may very well be deforming, not the studs. This would also explain why O rings have been very successful, where stock gaskets alone may have failed. Food for thought. [/QUOTE]
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