stainless steel bolts with brass inserts for a plastic intake manifold
hello, I’m redesigning an intake manifold joint on an IC engine where the upper and lower manifolds are plastic, and the factory setup uses M6 class 8.8 screws threading directly into plastic bosses. The plastic threads strip, so we’re planning M6 brass inserts and stainless steel bolts so the joint can be removed repeatedly. The original torque spec is 9 N·m, and I’m targeting a factor of safety of ~1.5, so about 15 N·m max. For this application, is a standard A2-70 / 304 stainless M6 bolt appropriate from a strength and torque standpoint, or am I risking bolt yielding or failure compared to the original class 8.8 fastener when torqued into brass inserts?