Originally Posted by radfordc

I think the concern is that during a cold start, if a cylinder has excess fuel/oil, when the piston comes up on compression it might over stress the cylinder casting and create a tiny stress fracture. Later when the engine is running this stress fracture could eventually fail. Full size radials are subject to the same thing.

http://www.avweb.com/news/pilotlounge/182680-1.html
"If you detect a hydraulic lock on a radial engine the only certain way to cure it is to remove the lower cylinder spark plugs and let the oil drain out. Pulling the prop through forward WILL result in a bent connecting rod and/or expensive damage to the engine if it does not cause a catastrophic failure. Pulling the propeller through backwards only reduces the chance of a bent connecting rod; it does not eliminate the risk"

https://en.wikipedia.org/wiki/Hydrolock
Hydrolock is common on radial and inverted engines (cylinders pointing downwards) when the engine sits for a long period. Engine oil seeps down under gravity into the cylinder through various means (through the rings, valve guides, etc.) and can fill a cylinder with enough oil to hydrolock it. The seepage effect can be observed by the blue-white smoke commonly seen when a radial engine starts up. In order to prevent engine damage, it is universal practice for the ground crew or pilot to check for hydrolock during pre-flight inspection of the aircraft, typically by hand-cranking the propeller for several turns to make sure the crankshaft cycles normally through all cylinders.