RE: Beware of O.S.
It shouldn't fall to us to check bolts and assembly, but it does. It takes all of 15 minutes to check inside the engine and flush it out and then check the torque on the backplate and head bolts and glow plug. The vast majority of engines that come of any of the factories are put together right, but we are the last line of QC before the engine goes into the airplane. I'm sure the manufacturers could offer a line of engines that have been checked over and broken in from the factory, but who would pay for them?
Smart flyers do the same thing to ARFs just in case something isn't right. Most of the time they find nothing wrong and go fly. But it's those rare times that they do that makes that extra little bit of effort worthwhile.