I have had the same problem, the rubber was hopping out, so I fixed the rubber with an extra screw, then it started to leak oil from the cylinder gasket, so I put some extra filling around the gasket and then I blow up both the blocks. I have teared the engine apart but still don't know what caused the problem, the only damaged thing I have found are the blocks, my best guess would be that an inner crack around the crank in the block causing some overpressure.
Hope it's just the rubber for you.