Well ... in my misspent youth (late 70's) a friend and I went to look at a BMW and he noticed that there were signs of exhaust gases at the base of one of the cylinders. Turned out that it had been dropped and the bolts holding the cylinder on were bent. Today, of course, we all use crash bars. And I did have an oilhead engine rebuild into a short block after someone backed into my bike while it was sitting on the center stand. A year later the block developed a crack where the center stand was mounted to the engine case - a fairly common piece of damage under similar circumstances.