James H. wrote:
What is the logic of banging DOWN on a lawnmower crankshaft in order to
lift a flywheel UP?


Someone else mentioned the vibration/shock of whacking something
with a hammer. It's an old trick that works for things like plumbing.
Hold one hammer on one side of the plumbing, hit the other side with
another hammer. Doing it in as many places as possible loosens up the
fittings.
Hitting a bolt head sometimes helps loosen it. It's seldom that I
hear of things vibrating tight.
If nothing else whacking something with a hammer a few times is a
good stress reliever.