I had my MVVS 45 quit running while in the air on a maiden flight, got the bird down for a nice landing.. Checked things over to find out why the engine died and couldnt find anything. At home I pulled the cylinder head to find a broken ring. Also in the exhaust port the vertical web had a bit of "slag" remaining from manufacter process. At that spot there is a void in the piston top down to the ring groove, I believe this to have torqued the ring causing it to break.
Sad part of this is I traded for this engine so I do not have a warranty. I believe the cylinder to be useable, have one super tiny mark that I can just barely feel with my fingernail length of the wall vertically, but I feel it is so small it will not pose any problems. However the ring and piston are toast.