It's a common missunderstanding that a wheels up landing on grass would be less harmful to an engine than on a paved runway. That's not really true! On soft ground the turning prop blades will dig into the ground while the airplane is still moving forward, creating an inevitably heavy bending force on the crankshaft. That's where the real problems start! But on a paved runway the shredding or bending of prop blades is "quick and painless", usually with little or more likely no damage to the crankshaft. The engine still have to be taken apart, but it's more likely that there is not to much or even no internal damage. The only real advantage of grass would be in case of a fuel leak.