The only place hard seats are a must would be in a Propane-powered engine. I worked at a concrete plant in California where most of our off-road equipment was Propane powered and we installed hard seats in all of those engines. The "lead is a lubricant" myth was debunked a long time ago, at least with all but a few diehard machine shop owners who see an opportunity to pad the bill when an older cylinder head comes in for a valve job. The shop where I managed the connecting rod rebuilding department did dozens of valve jobs a month, and we only installed hard seats in a very few situations with very special circumstances. We had virtually zero comebacks involving valve regression into the cylinder head on non-hardened valve seats. These are facts supported by actual excperience, not the equivalent of an "old wives' tale" that has been repeated by well-meaning but misinformed people. I call them "old mechanics' tales". Real world experience trumps a good-sounding theory any day.
Jerry
