I read from a lawncare forum that the 4 cycle Honda GX31 31cc engine have vibration problem at top RPM. The vibration were so bad that it actually crack the crankcase!!! Anyone have experience of this problem on the unmodified engine only. I can understand if you modify the engine, you are pushing it to the limit. But for an unmodified engine, it is hard to believe it would do this. Any comments?

Is the GX31 design robust or the GX35 is better?
Thanks