Anyone ever weigh the engine?

Its a known fact that our engines are a LOT more reliable than 250f dirt bike engines. I am wondering what the trade off is, why the dirt bike engines aren't as reliable. I know they run hotter cams to rev higher and have a higher compression ratio, but that shouldn't cause such a drastic difference. All I can think of is weight. It must be that the design that makes ours so much more reliable is too heavy for a motocross bike, and our bike is a whole lot heavier. I don't know how much of that is the chassis though. Anyone ever weigh our engine with it out of the frame?