Does anyone have hardened valve seats and/or new guides in 371 heads? My machine shop is skeptical because they think that if they install valve seats they might hit the water passage. Anyone know if it's possible?

 

Got them in my 324, no problems. Don't use chevy seats they are to deep ...Tedd

 

I'd rather use 1 part race gas with lead to 3 parts street gas, or maybe add the lead substitute. Of course, the EPA decided some years ago that it is illegal to use leaded gas on the street. Older heads were not designed with a lot of thickness to allow adding seats. Thus, the pressed in seats are marginally thick, and so are the heads after milling them for seats. Seat recession occurs mostly under high power, but can happen rather quickly.

 

Unless you're planning to run it 60,000 mies or more - don't bother!
I just started a thread on exactly this nonsense!!!

 

Try to figure out how deep you can go before hitting a water passage. Maybe someone here know it, or has a head that's cut open (heads beyond repair are never junk great research material)
Than you know how far you can go.
About 0.200" deep is normal for replacement valve seats. You can cut the height of the seat to any height you want, once it's in there. Just cut it flush with your combustion chamber.

The outer and inner diameter of your replacement seats are more important.

The way I see it, you can always cut away the existing valve seat. I know these old heads are all cast-iron and don't have pressed in seats, but you can see where it about starts. And just don't go deeper than that.