I came across an issue today that I have never heard or seen before. I recently bought a barely used tower .46 engine from the internet and have it mounted on the tower trainer .40. Took it out today for it's first flight and the engine gave a bad noise. When either hand flipping the prop or using a starter, at the top of the stroke, the engine will "lock" basically and make a knocking sound when you finish turning the prop over. I know that a compression tightness occurs at the top of the stroke in an ABC engine but this is not smooth and makes a loud racket. The engine starts ok, but the knocking sound is so annoying it sounds bad and so I didn't even want to continue to run the engine. Anyone have some tips or ideas? When you hand flip the prop, you can feel the "locking" at the top of the stroke and so makes me think it is a seating issue. But, I took the head off the engine and the piston seats fine without issues so makes me think it is the bearings??? Like I said before, the engine is barely used at all so I can't believe the bearings might be bad? Hope there is an easy fix like lubing the bearings?? [&:]