Long story shortened - the "clearance ramp" sections of a solid lifter grind were never intended to be used for lift - that's why the cam grinders card includes design specific lash specs. These specs are a compromise between duration, durability and chatter. As for the effects of thermal expansion - there are a whole lot of variables between cold winter ambient, summer day ambient and operating temperature. At initial startup the exhaust valves are the first component to heat up. If lashed too tight they cannot shed heat via the seats. Absent seat contact the heat will transfer up the stem - lengthening the valve in even further off the seat. The result will be burnt valves. The responses to your thread on
HAMB include many other reasons to not experiment with zero lash on an iron block iron head engine.
