A respected guru recommends 0.002" clearance on 172-FMM engines. Who is this? Joe Henner. No one checks the valve clearance when the engine is hot, but that would be the best time to verify that the gap hasn't closed.
A fully closed gap when the engine is HOT is no problem, as long as the valve is not slightly open. The main reason for a gap is to assure that the valve CLOSES when the engine is hot. Escaping gases burn through the valve seat. This is bad.
So I will stick with 0.001-0.002" on intake, and closer to 0.002 on exhaust. Do I have evidence for this? No. I just pretend to be a guru
After a lengthy session of valve adjustment, I discovered that about 1/8th turn loose from snug is about 0.002" or a little less. At least this was true when I did this. One of these days, maybe I will do a hot check
