I thought maybe the outer cylinders had run leaner/hotter, guess not though. Of the 5 Nova's I have owned the last three have been inline's and I have had no valve problems, I am not going to say that there is no advantage to hardened seats, (I currently run a non-integral smog head on my 250) but I have to agree with BOB308's advice because the same detonation/pre-ignition that sink's valves will "knock" loose hardened inserts too.
