If you recall back in the sunmer when due to shoddy dealer work and the right head bent two exhaust valves we talked about the fact you can only use the head bolts ONE time and must replace them once they are loosened up.
I did some research and now can see why its best they are replaced.
GM engineers decided to use torque angle to get critical fasteners in the Gen III engine to the proper clamping force.
Torque angle is an engineering term for the act of applying light torque force to the single use factory fasteners, then rotating the fastener a pre-determined angle of degrees to stretch it.
T/A is used on the fasteners that hold the crank main caps, rod end caps, cylinder heads, crank pulley and other key areas to attain the required clamping force.
Usually a component comes loose because either the fastener was not tightened enough to keep from backing out of its threads, or it was overtightened it lost its ability to hold the component (lost its stretch ability and clamping force), which both cases are bad for maintaining the engine properly together (which shows up even worse if the engine is boosted) .
GM uses TA because its a good way to create the appropriate clamping force on components, even with the many variations that occur in the production assembly process.
Because of this bolt stretching, GM recommends not reusing its production fasteners, like the head bolts.
If your using aftermarket fasteners the stretch information is often invalid, as they are more robust then stock ones are.
Incorrect use of stretch bolts such as overtightening will cause them to lose their clamping ability and if engine is boosted the problem will even be worse since it can cause the heads to lift slighty or crank pulley to back off.
Never use a sealer, locktight, etc on the threads of these types of fasteners and the threads bolt is screwing into must be clean so proper T/A and clamping force is maintained.
If engine is running at a high boost pressure it may be safer to even tap the block's mating holes to use even larger sized head bolts then stock to assure the heads are clamped better to reduce chances of head lift with high boost causing head gaskets to come apart or leak and add a metal O-ring to allow even more pressure onto a good copper gasket that is clear sprayed to prevent radiator fluid passing through that is common with a copper gasket but it will work better then stock head gaskets.
