Just remember, the vibration levels from a running engine can do far more damage than you can "feel" with your hand. I don't know about you, but I can't back out screws with my fingers, but my engine sure is good at it if I don't use locktite

Great advice from CafeenMan.

(oh, disclaimer time, I have acutally flown with cracked mounts, but as CafeenMan indicated, the crack was small, and in a location such that even if it failed, I'd lot have the engine come off. And it was on a plane that gets a lot of pre-flight attention and maintenance anyway).