Hi!
What do you mean??
"the piston wasn't seated in the crank pin properly"

The piston is running in the cylinder liner...and the piston has in it's center a piston rod...that is connected to the connecting rod which in turn is connected to the crank pin and crank shaft...that spins the propeller around.
All these parts are mounted correctly if the engine can be run. So the crank pin cannot be loose...or mounted incorrectly if you have been able to run the engine!

So what was wrong?? Just curious!