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To prevent leakage, the whole system "floats" the intake valve cover (VC) between two rubber cushions (VC gasket and the rubber washers) and relies upon these to maintain their pliability and not permanently deform . The gasket has way more surface area than the sum of the washers, so the washers are already on the losing end if we consider preload per unit area. Also, the gasket has more cross section than the washers, so its percentage of crush is less and it doesn't permanently deform as much as the washers do. In addition, it maintains a it's pliability better (this is probably due to it being a better heat/oil resistant material than the washers). The OE plan to prevent the rubber washers from being crushed too far was to put shoulders on the VC bolts which don't fit through the VC bolt holes. I view this as more of an assembly aid to speed up the production process... This probably works well enough to get the vehicle beyond the warranty period, but as we all know with enough time and heat the washers deform, harden, and lose the preload they were contributing to the VC and it's gasket... loss of preload leads to loose bolts and oil leaks. What I found is the VC gasket's optimum crush is when the VC is held roughly 0.060" off of the head's gasket surface. I merely supplied some 0.060" spacers with my intake VC bolt kits to hold the VC at the proper height along with shorter ARP bolts and this allowed the intake VC to be attached rigidly rather than floating between two rubber cushions (no more loss of preload or bolts coming loose). The problem with my system is the spacers are small and easy to drop into the head during installation, so it isn't very user-friendly and I quit selling the kit until I can find a better way to shim the VC... unfortunately the better solutions all increase the price.
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