Ah! If it was only that simple!!
http://en.wikipedia.org/wiki/Torsional_vibration
With the clutch engaged there is enough mass to provide some torsional damping, without there obviously isn't!
This engine or other derivatives also has an issue when it lives its life with a propeller connected to it as well - see Piper Arrow, Cessna 177 for examples.
On overspeed - more than 3350, this engine will crack the valve collets which can also rip your nightie!