hardened valve seats for Unleaded fuel

[Boyscout]

The valve was re ground so it would seal against the newly cut valve seat.

[2y2m2]

Why only exhaust valves? surely all seats need to have hardened inserts? I know that the inlets would run cooler than the exhaust -?

[Boyscout]

Only the Exhaust valves experience "micro welding" of the valve to the seat which leads to valve seat erosion. The inlet valve is constantly cooled by the cooler inlet air and does not suffer from valve seat recession. Nothing stops you from doing the inlet seats as well though.

[2y2m2]

ok- thought it might have something to do with the temp. And micro-welding is something I'm new to. I've heard though, that the cut, cast-iron seats get pressed deeper into the head due to lack of "lubrication" when using unleaded petrol?

[theMINIguy]

?? The head itself is the cast iron material from which the stock seats are cut... they can't move they are part of the head, they can only erode.

[2y2m2]

yes, I meant that the seat shape gets bashed deeper into the head- got see if I can find where I read that, somewhere, some place over the rainbow...

[2y2m2]

yes, I meant that the seat shape gets bashed deeper into the head-  got see if I can find where I read that, somewhere, some place over the rainbow...

Here is an article that mentions both problems- recession and welding :-) :-)
http://www.rmahc.com/valveseat.html