Valve adjustment frequency and lead additive

On my 223, the valves need to be adjusted much more frequently than the 12k mile recommended interval. I am having to adjust them after a few thousand miles and finding that they are tight, not loose.

The only explanation I can come up with for this is valve recession into the head. The head is original so the valve seats are not hardened. I have never had issues running unleaded gas in other engines of this vintage, so this is a new scenario to me. Is lead additive/substitute an effective or necessary solution?

Sounds like your valve seats are deteriorating, due to the use of unleaded fuel. I rebuilt my first engine in 1973 (a 1955 Ford 272 Y-Block) and was told I would need to get the heads re-seated with flame-hardened seats.
There could be a danger of ending up with bent push-rods if valve seats are not corrected, but at some point you end up with no valve seats at all, until you change to annealed seats.

There is a lead-substitute additive available at some chain auto parts stores. Maybe you can get by using it temporarily until heads are rebuilt, but I have no faith in that.

This is definitely valve recession. I pulled the engine and removed the cylinder head to find marked valve recession on all exhausts. Cylinders 3 and 4 are the worst; one of them is perhaps slightly below the combustion chamber surface.

I haven’t removed any valves yet but obviously there will be some parts needed to rectify this. I have heard that when switching to hardened valves/seats that only one of the two need by hardened—either the valves OR the seats. Is this correct?

peeeot":13mse9vx said:

This is definitely valve recession. I pulled the engine and removed the cylinder head to find marked valve recession on all exhausts. Cylinders 3 and 4 are the worst; one of them is perhaps slightly below the combustion chamber surface.

I haven’t removed any valves yet but obviously there will be some parts needed to rectify this. I have heard that when switching to hardened valves/seats that only one of the two need by hardened—either the valves OR the seats. Is this correct?

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The head will have to be machined and a new hardened seat pressed it. It the valve is harder than the seat, well, you already have that problem...