I had a machine shop look at the heads and even replace all the valves too because the 318 I had them on before broke a valve and had bent most of the others too(poor clearance in the bore). Like I mentioned before, the engine was still on its break-in period so high revving was off the table, at that point there's no way I could've floated the valves. It could've been a preload issue but I did cylinder 5 with the same preload as all the rest, why would this one let loose?