Okay I'm no professional like several of you guys. I'm just a garage hack and build my own motors. I was not aware that the guides needed sized different for marine use, and I'm not suggesting that they don't need special clearances. However, given the number of engines I have built over the years, without any guide failures, leaves me wondering why they need special sizing, or why I haven't had any guide issues? My latest build (Dyno Results) used AFR heads but my head guy supplied the valves and springs. Since the new motor currently has less than an hour of run time, off the dyno, do I need to pull the heads to check the guides?