Joe H You know they knew clear back in the fifties that valve seats had to be dealt with to run vapor type fuels. Induction hardened GM valve seats with modern high quality valves work fine. Once the seats are ground it's over gotta have seat rings on engines that are really loaded and working hard. As I have said before on a light weight,around town pickup truck it will run quite a while with what is in there. My 235 51 6400 is coming up on 12,000 miles that way. I called Goodsons and bought valve seats put em in a 235 re-build,later called for more he said oh don't use those for propane,well they have run over 12 years now so go figure. Apparantly no-lead seats will work too !
