Bill,
I thought the first heads made to be used for unleaded were flame hardened, not made with a hardened seat insert ??
Am I wrong here??
You're right, from what I remember (and it ain't what it used to be) the mid 70's heads were the first to have hardened seats. They were induction or flame hardened, I can't remember the exact process. The problem was that the hardened layer was very inconsistent; thin in some spots & thicker in others. It's possible to grind right through the thin layer when doing a valve job. The seat recession problem isn't really widespread, but if you're going to the trouble to refurbish the heads, then why not do it right the first time & not have to worry about it? The heads may show no wear when torn down, then the seats are ground, the hardened layer goes away, then the valves sink, & you have to do the job over & install the seats. More time & money spent. Or just buy the lead additive or pour a pint of Marvel Mystery oil in the tank when you fill up.
Just my $.02
BL
