I was helping out with an event at our field this weekend when this happened. A plane was in the air when it made what to me was an out of the ordinary sputtering noise and then dead sticked. I know little or nothing about rc gas engines, but when it died, it sounded bad. The pilot landed it without too much problem. The picture below shows what caused the noise.

A veteran in gas engines believed the cause was the way it was mounted. The washers and spacers weren't even causing the crank case to twist a bit. The casing itself seemed to be awful thin in spots, but maybe that is the norm.