Do the valve guides in 240Z engines require leaded fule for proper lubrication and sealing? Or am I missing something?

To my knowledge the lead content of fuel was not to lubricate, like a graphite compound but to absorb heat from the exhaust valve and seat and draw it away with the expelled exhaust gases (is that a tautology ?!)

In my experience the conversion to "unleaded" was mainly the use of stellite or hardened exhaust valve seats? We did the guides (k-line) just 'cause the heads were off and the valves were out and as a concession to the hours they had done.

Hopefully someone who does this every day will jump in and make it clearer?

P.S. I've been told (by an engine builder I respect) an L series is still good for 100,000 Kms + on the original valve gear and unleaded fuel

Edited March 25, 201114 yr by g72s20
a bit more info!

MSA (Motorsport Automotive) sells stainless guides to upgrade from the bronze ones that the early leaded fuel cars used.

It's my understanding, from conversations with a few guys that ran 240Z'z at the 24 hour Daytona event, that the lead residue actually lubricates the valve stems. It also "builds up" on the actual seat area of the head, both intake and exhaust, and fills the micro pours in the castings creating a better seal. Additionally, it benifits the valve seals and as stated by g72s20 aids in heat disapation. The residue effects make sense to me when I think about the affects of leaded fuel on the cataletic converter.

That said, I run lead additive in my Z. It totally eliminates detonation and helps the fuel stay fresh while the car sits. I guess I'm just looking for insight from others to confirm or dispute the info I gathered from the Racers crew.

I recall reading, relatively recently, in an early 1970s Road and Track during the great unleaded fuel change over that it turned out not to be a big deal. Basically, engines that needed lead for the valve train could run without harm on unleaded fuel because the lead in only a few tanks was sufficient to protect the engine for life. Pretty sure, in fact, that GM concluded that one tank of leaded was sufficient. I doubt they contemplated 40 year old engines with 250K+ miles on them when making this conclusion, but the mechanism by which it worked was similar to that described by 5thhorsemann and its possible that once part of the metal, it doesn't come off easily, so whether they were thinking 10 years and 100K or 40 years and a quarter million it doesn't matter much.

Chris