Perhaps I should define "really tight" as plenty tight enough (especially with lock tight) but not as tight as I can make it. I have broken lots of bolts in my day so I go easy on stuff. If I want it to stay together I just put some locktight on it. Also, your right about the crankshaft having lots of vibration and rotational stress while running (which the lock tight is designed to address), but the stress you put on something pressing together is completely different. How often have you heard of a lug nut fail due to rotational forces vs over tightening? Also, don't under-estimate how much force you can put on something. Once I broke off a 5/16 bolt in the clutch on my snowmobile with a hand wrench and I'm not a very big guy.