HARDENED VALVE SEATS

Ancient history. Somewhere on the Web is a series of studies done in the mid-'70s on the effects of unleaded gas on passenger-car engines. Briefly, it was found by long-haul trucing companies, that unless the engine in question was being run many hundred thousands of miles a year (as in transcontinental trucks), the effect of lead-oxide in cushioning the valves on the seats and preventing seat recession was a myth. With "moderate" use- say, ONLY 100,000 miles a year, NO effect was seen from using leaded vs unleaded fuel. The only thing Ford (and GM) did re this problem in all the years was to use induction-hardened valve seat areas in their later cast iron heads, and this treatment was so thin, it seldom survived 2 valve jobs. IMHO, the only good coming from adding hardened seats is-
1)- they rescue badly-corroded or over-ground closed-chamber heads that otherwise would be thrown away.
2)- if you're using propane as a fuel. Propane is an extremely hot-burning, "dry" fuel that WILL cause valve-seat recession in cast iron heads. Possibly, long-term use of turbochargers might do the same (a guess).
3)- it keeps engine shops busy ($20 a seat is what I remember)

Thanks Jack! I had read back in the '70's, or was it the 80's, that the valve seat problem did NOT turn out to be the BIG problem the engineers had originaly thought it was going to be. This after they had opened up quite a few New York Taxi cab engines with hundreds of thousands of miles of stop and go, and freeway, traffic on them. I think your right about the machine shops making a good business out of it; because it was from a shop that I purchased my set of closed chambered heads. The machinist had caused me concern as he stated "be sure to have hardened valve seats put on the exhausts, or those heads won't last 5000 miles." So now I think I will save the money and not worry about it, as my 74 cleveland purrs along beautifully with over 46,000 miles on it. Thanks for the info! Regards, Marlin.

[This message has been edited by MARLIN JACK (edited 09-08-2002).]

As for fixing corrosion problems, this is the scenario- all those closed-chamber heads are now 30+ years old. Many sit in junkyards across the US, in cars with the hood open, or no hood at all, and it does rain /snow. The carb is the first thing scavenged off a wreck so this leaves the intake open to weather. At least one intake & one exhaust valve will be held open when the engine stopped for the last time, so water will fill up the cylinder. The seats rust & pit and the head is junk- unless you pop for hardened inserts.

i belive the type of cam might also play a part in it. my fatner had a mecanical cam in his engine and about 5 years ( volvo crate engine for a p1800) it it pounded in the valve seats while his old chevy with the hydraulic cam has no probles yet wit the valve seats.