Hot mess, a 1967 CJ-5 restoration

[bmorgil]

Industrial engines and truck motors etc., sometimes had the seats hardened way back in time. As gm has said however, passenger car engines not until the mid 70's. By 1986 fuel was completely lead free. The effect of the lack of lead in the fuel is most pronounced in hard working engines. I have had the opportunity to see quite a few engines that suffered from exhaust valve seat recession. Early attempts to stop it with valve rotators and the like, helped. The harder an engine is working, the more the effect will be. I have seen engines come apart with relatively low mileage, no hardened seats and have exhaust valve recession. I have also seen high mileage with little to no effect. It truly depends on how much load, RPM and time spent under load. There was still some lead in the fuel, gradually phasing it out by 1985 or so. Engines built prior to the mid 70's without hardened seats started showing up with recession in the late 80's, as lead was completely phased out by 1985 - 87. I saw first hand more than one cylinder head with the exhaust valves sunk in so far the engine would no longer run.

I wouldn't sweat this too much. If you are not sure if you have hardened exhaust seats, an occasional tank of no-lead wont hurt. A can of top end lube in the fuel once and a while will do just fine, unless you are towing a lot or running at full load for extended periods. The ethanol in the fuel is more destructive to parts that are incompatible, like pre-80's fuel lines.

The only way to know if someone has installed hardened seats or, if the seats were originally induction hardened, is a visual inspection. Did you have a valve job done on this engine? if so the machinist would know.