Here's some tech from a valve seat manufacturer that could save you some very costly repair work on engine rebuilds. Things have changed in valve and seat metallurgy that make practices like "interference angle grinding" obsolete- now more than ever you have to inquire about what's going into your engine. Links- www.sbintl.com/tech3.html (LPG engines), www.sbintl.com/tech6.html (valve life), www.sbintl.com/tech7.html (valve seats).